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Because three cases of a very rare brain cancer have been detected in children living in a small community located near a hazardous waste disposal site, local clinicians want to determine if they can identify risk factors associated with cancer development. They should conduct a ______ to address this question. A)case-control investigation B)controlled clinical trial C)prospective cohort study D)cross-sectional study

A)case-control investigation\ Key point - case-control studies are best for RARE diseases. This will likely be on the boards and will be on the exam.

15. A test for celiac disease is being evaluated. It is called the GLUTINO test. Five hundred people are given both the GLUTINO test and a small bowel biopsy. The small bowel biopsy is felt to be the gold standard for the diagnosis of celiac disease. One hundred people had a positive GLUTINO test, the rest tested negative. Of the one hundred people with a positive GLUTINO test, 90 also had a positive small bowel biopsy. Of the 400 with a negative GLUTINO test, 350 had a negative small bowel biopsy. What is the false positive error rate for the Glutino test based on this study? A.0.03 B.0.10 C.0.13 D.0.36 •

A.0.03 False positive error rate = (false positives)/(all those without disease) = b/(b+d) = 10/360 = .027 = approximately .03 The proportion of those WITHOUT disease who will test positive, even though they don't actually have the disease. The proportion of those without disease who will have a false positive test.

Researchers wish to study the relationship between stroke in women at a young age (defined as under age 50) and oral contraceptive (OCP) use. They enrolled 100 women who had a history of stroke occurring prior to age 50-years and 100 controls. The controls were women under age 50-years who had no history of stroke. All participants were interviewed and use of OCPs were documented. Seventy-five of the cases had a history of OCP use and 50 of the controls had a history of OCP use. What is the most appropriate measure of association and what is the value of this measure? •

Answer: The ODDS RATIO (OR) and the value is 3

how to do a nonogram

12. A test for celiac disease is being evaluated. It is called the GLUTINO test. Five hundred people are given both the GLUTINO test and a small bowel biopsy. The small bowel biopsy is felt to be the gold standard for the diagnosis of celiac disease. One hundred people had a positive GLUTINO test, the rest tested negative. Of the one hundred people with a positive GLUTINO test, 90 also had a positive small bowel biopsy. Of the 400 with a negative GLUTINO test, 350 had a negative small bowel biopsy. What is the Sensitivity of the Glutino test based on this study? A.0.64 B.0.88 C.0.90 D.0.97 •

A.0.64 Sn = true positive/all who have disease = a/(a+c) = 90/140=.64

5. Which of the following types of studies is subjected to the greatest amount of recall bias? A.Case-control studies B.Cross-sectional ecologic studies C.Prospective cohort studies D.Randomized controlled trials }

A.Case-control studies With case-control studies the people who have the disease or condition of interest are identified and then prior records and/or interviews are used to determine their risk factors. Someone who has a disease might RECALL his or her risk factors differently than someone who does not have a disease. Recall bias is a serious problem for case-control studies.

8. Researchers wish to study the association between Bowen's Syndrome and smoking. Researchers identified 100 people with Bowen's Syndrome and matched them with 100 'controls' who do not have Bowen's Syndrome. All participants were interviewed and asked about their history of smoking. Of those with Bowen's Syndrome, 30 have a history of smoking. Of those without Bowen's Syndrome, 25 have a history of smoking. What type of study is this? A.Case-control study B.Prospective cohort study C.Randomized controlled clinical trial D.Retrospective cohort study

A.Case-control study This is a case-control study. Those with the condition of interest (Bowen's Syndrome) were identified. They were then matched with controls.

3. _______ is the false assumption that individual members of a group have the average characteristics of the large group. A.Ecological fallacy B.Length bias C.Overmatching D.Placebo effect E.Selection bias }

A.Ecological fallacy

1. Researchers wish to study the association between hybrid vehicle use and the development of carpal tunnel syndrome. Two hundred hybrid vehicle drivers were enrolled in the study and two hundred people who drive other types of vehicles were enrolled. All participants received a baseline history and physical exam. The participants were followed for two years. At the end of the two years there were 30 people with carpal tunnel in the hybrid vehicle group and 15 people with carpal tunnel in the other vehicle group. What is the most appropriate measure of association for this study and what is the value of this measure? A.Relative risk, value is 2 B.Relative risk, value is 0.5 C.Odds ratio, value is 2.18 D.Odds ratio, value is 0.5 ●

A.Relative risk, value is 2 This is a prospective cohort study. You will want to calculate relative risk. Create your 2 x 2 table and plug in the values. Then calculate the RR.

17. The positive likelihood ratio associated with the use of the Thyroid Simulating Hormone (TSH) test for Hypothyroidism varies with the ______________. A.cutoff point B.negative predictive value C.positive predictive value D.prevalence of disease in the population •

A.cutoff point The best answer is the cutoff point. Likelihood ratios are NOT influenced by the prevalence of disease. This makes sense because they can be calculated from the sensitivity and specificity (which are TEST properties). Moving the cutoff point of a test affects the test properties. The cutoff point directly affects sensitivity and specificity.

2. Cross-sectional surveys are subject to _________ bias, because they select for longer lasting cases. A.late look B.recall C.publication D.selection

A.late look Compare and contrast the observational designs for generating hypotheses. Disadvantages of cross-sectional surveys include: Can't determine cause and effect. No information about temporal relationship. Exposure to risk factor and presence or absence of disease measured at same point in time. Subject to late look or length bias (selects for longer lasting cases, not rapidly fatal diseases).

•Researchers wished to investigate the potential relationship between soccer playing when young and ACL tears in girls and young women. They enrolled 200 girls who played soccer and were between the ages of 8 and 10. They also enrolled 200 girls who were between the ages of 8 and 10 but who did not play soccer. All of the girls were followed for 10 years. The girls were interviewed yearly, medical and surgical histories were recorded. Specifically they determined if there was a history of an ACL tear. •What type of study is this? A)case-control study B)Prospective cohort study C)Retrospective cohort study D)Randomized controlled clinical trial

B)Prospective cohort study Enrolled based on risk factor. Followed forward over time and outcome is looked for. The outcome of interest in this study is the development of an ACL tear. This is the "Disease." You will notice that the "disease" is not always what we think of as a "disease."

7. A randomized controlled clinical trial showed a mortality benefit from a new breast cancer chemotherapy. Women with breast cancer were enrolled. Inclusion criteria included those with stage IV breast cancer. Exclusion criteria included anyone over age 50 and those with cardiovascular, renal or endocrine abnormalities. The trial was triple-blinded and participants were randomized to treatment or control groups (control groups received the standard breast cancer treatment). This study will have problems with _____. A.allocation bias B.external validity C.internal validity D.over matching

B.external validity

9. Researchers wish to study the association between hybrid vehicle use and the development of carpal tunnel syndrome. Two hundred hybrid vehicle drivers were enrolled in the study and two hundred people who drive other types of vehicles were enrolled. All participants received a baseline history and physical exam. The participants were followed for two years. At the end of the two years there were 30 people with carpal tunnel in the hybrid vehicle group and 15 people with carpal tunnel in the other vehicle group. What type of study is this? A.Case-control study B.Prospective cohort study C.Randomized controlled clinical trial D.Retrospective cohort study

B.Prospective cohort study

1. Examining new data to determine if predictions are correct is _______. A.hypothesis generation B.hypothesis testing C.not possible with randomized controlled trials D.possible with cross-sectional surveys }

B.hypothesis testing RCTs can be used for hypothesis testing. Cross-sectional surveys can not be used for hypothesis testing.

A triple-blinded, randomized controlled clinical trial evaluated the potential benefits from the use of aspirin. Two thousand men who were cancer free and between the ages of 40 and 60-years were enrolled in the study. Half were randomly assigned to daily aspirin use and half were randomly assigned to placebo. The men were followed for 20 years and evaluated for the development of colon cancer. Fifty people in the treatment group developed colon cancer and 200 in the control group developed colon cancer. An evaluation of harm was also undertaken. Four hundred in the treatment group experienced a Gastrointestinal (GI) bleed. Two hundred in the control group experienced a GI bleed. 1. What is the absolute reduction in the risk for colon cancer from the treatment with aspirin? A..05 B..15 C..2 D..25 •

B..15

5.A prospective cohort study was undertaken to evaluate the effects of exposure to second hand smoke on asthma development. Two hundred children who were exposed to second hand smoke and 200 children who were not exposed, were followed for 10 years. Asthma development was recorded. Seventy-five of those exposed to second hand smoke developed asthma. Twenty of those who were not exposed developed asthma. What is the attributable risk of asthma from second hand smoke exposure? A..1 B..28 C..38 D.3

B..28 Attributable risk = risk difference = risk (exposed) - risk (unexposed) = 75/200 - 20/200 = .375 - .1 = .275 = approximately .28

7. A test for gestational diabetes is being evaluated. The test is called the Gestational Diabetes Sugar Free Test (GDSFT). It involves a simple blood test. To evaluate the test the researchers used the test on two hundred pregnant women. The women also received a glucose tolerance test, considered the gold standard for diagnosing gestational diabetes. The GDSFT was positive in 75 women and negative in 125. Among those with a positive GDSFT, 50 also had a positive glucose tolerance test. Among those with a negative GDSFT, 20 had a positive glucose tolerance test. What is the Sensitivity of the GDSFT as determined by this study? A.0.66 B.0.71 C.0.81 D.0.84 •

B.0.71 Sensitivity = true positive / All those with disease = a/(a+c) = 50/70 = .71 or 71%

14. A test for celiac disease is being evaluated. It is called the GLUTINO test. Five hundred people are given both the GLUTINO test and a small bowel biopsy. The small bowel biopsy is felt to be the gold standard for the diagnosis of celiac disease. One hundred people had a positive GLUTINO test, the rest tested negative. Of the one hundred people with a positive GLUTINO test, 90 also had a positive small bowel biopsy. Of the 400 with a negative GLUTINO test, 350 had a negative small bowel biopsy. What is the Negative Predictive Value of the Glutino test in this population? A.0.64 B.0.88 C.0.90 D.0.97 •

B.0.88 NPV = true negative/all who TEST negative = d/(c+d) = 350/400 = .875 = approximately .88 or 88%

B.33% Specificity = true negative/ (all those without disease) = d/(b+d) = 50/150 = .3333 or 33%

4. A type of research study useful for both generating and testing hypotheses, where the study group is assembled in the present time, baseline data and information on risk factors are collected and then the group is followed over time is a _______. A.case-control study B.prospective cohort study C.randomized controlled clinical trial D.retrospective cohort study }

B.prospective cohort study Prospective Cohort Studies: Assemble the study group in the present time, collect baseline data and then continue to follow and collect data over time i.e. years. Control and standardize the data as it is collected. Check for outcome events. The estimates of risk are true (absolute) risks for the groups studied (not limited to relative risks between groups). Can study many different disease outcomes and relate them to the risks observed over time.

19. To determine the best cutoff point for a diagnostic test various factors are taken into account. There is a tradeoff that must occur. What statement best characterizes the overall goals and the tradeoff when setting the cutoff point? You wish to set your cutoff point at a level where ________________________. A.sensitivity is maximized and specificity is minimized B.sensitivity is maximized and false positives are minimized C.sensitivity is maximized and false negatives are minimized D.specificity is maximized and false positives are minimized •

B.sensitivity is maximized and false positives are minimized There is a tradeoff between false positives Sn = Sensitivity = a/(a + c) = true positive over all those with disease, we want to capture those with disease when we do a screening test. We want a high portion of true positive to be found relative to all those with disease. Minimizing c (false negatives) makes this ration closer to (a/a ) or 1 or 100% sensitive. The point is, you want to set your cutoff point at a level where you can maximize sensitivity and also minimize false-positives. Remember, high sensitivity means low levels of false-negatives (screening tests want to capture all those with disease). The "cost" of having low levels of false-negatives is that you will end up with false-positives. The ROC curve gives us a picture of this trade-off. For those of you who like math, think of it this way, the best test maximizes the area under this curve.

•Patients with a rare and often fatal eye cancer (ocular melanoma) were assigned randomly to undergo conventional treatment, which involves removing the affected eyeball, or an experimental therapy, in which a small plastic disc containing radioactive iodine is attached surgically to the back of the eyeball, which is left in place. Patients are followed for 10 years to determine the proportion of participants alive at the end of the follow-up period and mean survival time (months). •This study is an example of a (an) __________. A) prospective cohort investigation B) case-control investigation C) uncontrolled clinical trial D) controlled clinical trial E) cross-sectional investigation

D) controlled clinical trial

18. A ten-year-old boy presents with cough and sore throat. The patient has not had a fever. The patient has a history of strep throat. His father is concerned that the patient might have strep throat again and they are leaving for vacation shortly. The father would like antibiotics. On exam the boy does not have fever, pharyngeal exudate or lymphadenopathy. Based on his history and physical you estimate his pre-test probability of having strep throat as low. You feel the probability is only 15% that he has strep throat. You perform a rapid strep test. The Sensitivity of the test is .90, the specificity is .95, the LR + for the test is 18 and the LR - for the test is .11. The rapid strep test comes back positive. What is the probability that the patient has strep throat given this positive test? [Odds of outcome X = (Probability of outcome X)/(1 - Probability of outcome X)][Probability of outcome X = (odds of outcome X)/(1 + odds of outcome X)] A..64 B..72 C..76 D.2.7 E.3.2 •

C..76 Please see handwritten calculations. Start with the pre-test probability, convert this to pre-test odds. Multiply the pre-test odds by the LR+, this gives you the post-test odds of strep throat. Then you need to convert the post-test odds back to probability. You see the question asks, what is the probability that the patient has strep throat given this positive test. There is a 76% probability that he HAS strep throat. Please note, there is a 24% chance that he does not have strep throat.

C.0.35 AR = risk difference = a/(a+b) - c/(c+d) = 50/100 - 30/200 = .5 - .15 = .35

8. A test for gestational diabetes is being evaluated. The test is called the Gestational Diabetes Sugar Free Test (GDSFT). It involves a simple blood test. To evaluate the test the researchers used the test on two hundred pregnant women. The women also received a glucose tolerance test, considered the gold standard for diagnosing gestational diabetes. The GDSFT was positive in 75 women and negative in 125. Among those with a positive GDSFT, 50 also had a positive glucose tolerance test. Among those with a negative GDSFT, 20 had a positive glucose tolerance test. What is Specificity of the GDSFT as determined by this study? A.0.66 B.0.71 C.0.81 D.0.84 •

C.0.81 Specificity = true negative / all those without disease = d/(b+d) = 105/130 = .807 = approximately .81 or 81%

11. A test for celiac disease is being evaluated. It is called the GLUTINO test. Five hundred people are given both the GLUTINO test and a small bowel biopsy. The small bowel biopsy is felt to be the gold standard for the diagnosis of celiac disease. One hundred people had a positive GLUTINO test, the rest tested negative. Of the one hundred people with a positive GLUTINO test, 90 also had a positive small bowel biopsy. Of the 400 with a negative GLUTINO test, 350 had a negative small bowel biopsy. What is the positive predictive value of the GLUTINO test in this population? A.0.64 B.0.88 C.0.90 D.0.97 •

C.0.90 PPV = true positive / all who test positive = a / (a + b) = 90/100 = .90 or 90%

A triple-blinded, randomized controlled clinical trial evaluated the potential benefits from the use of aspirin. Two thousand men who were cancer free and between the ages of 40 and 60-years were enrolled in the study. Half were randomly assigned to daily aspirin use and half were randomly assigned to placebo. The men were followed for 20 years and evaluated for the development of colon cancer. Fifty people in the treatment group developed colon cancer and 200 in the control group developed colon cancer. An evaluation of harm was also undertaken. Four hundred in the treatment group experienced a Gastrointestinal (GI) bleed. Two hundred in the control group experienced a GI bleed. 4. Based on this study, after treating approximately how many men with aspirin would you expect to see one case of GI bleeding? A.2 B.4 C.5 D.7 E.20

C.5 NNH = 1/ARI = 1/.2 = 5 ARI = 400/1000 - 200/1000 = 200/1000 = .2 = risk in treatment group - risk in control group

A triple-blinded, randomized controlled clinical trial evaluated the potential benefits from the use of aspirin. Two thousand men who were cancer free and between the ages of 40 and 60-years were enrolled in the study. Half were randomly assigned to daily aspirin use and half were randomly assigned to placebo. The men were followed for 20 years and evaluated for the development of colon cancer. Fifty people in the treatment group developed colon cancer and 200 in the control group developed colon cancer. An evaluation of harm was also undertaken. Four hundred in the treatment group experienced a Gastrointestinal (GI) bleed. Two hundred in the control group experienced a GI bleed. 2. What is the relative risk reduction in the risk for colon cancer from the treatment with aspirin? A.15% B.25% C.75% D.400%

C.75% RRR = .15/.2 = .75

2. The Pathology department at St. Mary's medical center requires that all pap smears be examined separately by three Pathologists. Each Pathologist examines the pap smears only once and makes a diagnosis. Each Pathologist is blind to the other Pathologists' diagnosis. The lab supervisor does not examine the specimens. However, she evaluates all readings for variability. What type of variability is the supervisor evaluating? A.Differential error B.Intraobserver variability C.Interobserver variability D.Random error •

C.Interobserver variability

A new rapid strep test for beta-hemolytic strep infection "Strep Throat" is developed. The developers of the test state it is even faster than the presently available rapid strep tests. This one is called the SRST. To evaluate the test, 500 patients with sore throat are enrolled in a study. All receive the SRST test and a throat culture. The culture is felt to be the gold standard for the diagnosis of Strep Throat. The SRST test is positive in 300 and negative in 200. Of the 300 with a positive SRST, 200 have a positive throat culture for Strep Throat. Of the 200 with a positive SRST, 150 have a positive throat culture for strep throat. 6. The manufacturers are unhappy about the evaluation of their SRST test. They insist on re-evaluating the test by applying it to 500 more patients. These patients have sore throat and pharyngeal exudate and a history of Strep Throat. The manufacturers feel that having a study group with a higher prevalence of disease will improve their product's performance. If the new group does have a higher prevalence of disease (as expected by the more symptoms suggestive of strep throat) the manufacturers can expect this new evaluation to show ______________. A.no change in the SRST test's positive predictive value, sensitivity or specificity. B.no change in the SRST test's positive predictive value or specificity but an increase in sensitivity. C.an increase in the SRST test's positive predictive value but no change in sensitivity or specificity. D.an increase in the SRST test's positive predictive value and sensitivity but no change in the specificity.

C.an increase in the SRST test's positive predictive value but no change in sensitivity or specificity. The take home point here is that SENSITIVITY AND SPECIFICITY ARE NOT AFFECTED BY PREVALENCE OF DISEASE. THIS IS A KEY POINT I WANT YOU TO KNOW. THESE ARE TEST PROPERTIES. You should also know that when there is a higher prevalence of disease then the positive predictive value of a test is higher. The Positive Predictive Value (PPV) answers the following question. What is the probability that this patient has the disease if his or her test is positive? If you have a high prevalence of disease then the overall probability that any patient has the disease is higher. With a higher prevalence then the probability that a patient with a positive test has the disease is also higher. So the answer to this question is C. With increased prevalence you'll have an increased PPV but NO CHANCE IN SENSITIVITY OR SPECIFICITY.

10. The true value of Mr. Smith's weight is 185 pounds. His bathrooms scale measures his weight to be 195 pounds. Concerned about potential weight gain he steps on and off of his scale 10 times and gets the following readings. 195 lbs, 186 lbs, 199 lbs, 172.5 lbs, 199 lbs, 165 lbs, 185.5 lbs, 199 lbs, 165.5 lbs and 156 lbs. The readings from this scale are ______________. A.accurate but not precise B.both accurate and precise C.neither accurate nor precise D.precise but not accurate

C.neither accurate nor precise This time the values are not close together OR close to his actual weight. This scale is neither accurate nor precise.

What happens to Sn, Sp, PPV and NPV if the prevalence of disease increases?

•Sn and Sp are TEST Properties, these will not change with a change in prevalence. • •The PPV will increase with an increase in the prevalence of disease. •The NPV will decrease with an increase in the prevalence of disease.

•Researchers wish to study a new antibiotic (X) to treat community acquired pneumonia (CAP). Five hundred patients with CAP were enrolled in the study. Those enrolled were randomly assigned to the treatment group with drug X or the control group with standard therapy. Half were assigned to each group. They were evaluated for full recovery within one week of treatment. In the study group 150 recovered within one week. In the control group 50 recovered within one week. What type of study is this? A)Case-control study B)Prospective cohort study C)Retrospective cohort study D)Randomized controlled clinical trial •

D)Randomized controlled clinical trial

15. A test for celiac disease is being evaluated. It is called the GLUTINO test. Five hundred people are given both the GLUTINO test and a small bowel biopsy. The small bowel biopsy is felt to be the gold standard for the diagnosis of celiac disease. One hundred people had a positive GLUTINO test, the rest tested negative. Of the one hundred people with a positive GLUTINO test, 90 also had a positive small bowel biopsy. Of the 400 with a negative GLUTINO test, 350 had a negative small bowel biopsy. What is the false negative error rate for the Glutino test based on this study? A.0.03 B.0.10 C.0.13 D.0.36 •

D.0.36 False negative error rate = (false negatives)/(all those with disease) = c/(a+c) = 50/140 = .357 = approximately .36 This is the proportion of those WITH Disease who will test negative (even though they actually HAVE the disease). These are the false negatives relative to all those with disease. The proportion of those with disease who will have a negative test.

9. A test for gestational diabetes is being evaluated. The test is called the Gestational Diabetes Sugar Free Test (GDSFT). It involves a simple blood test. To evaluate the test the researchers used the test on two hundred pregnant women. The women also received a glucose tolerance test, considered the gold standard for diagnosing gestational diabetes. The GDSFT was positive in 75 women and negative in 125. Among those with a positive GDSFT, 50 also had a positive glucose tolerance test. Among those with a negative GDSFT, 20 had a positive glucose tolerance test. What is Negative Predictive Value of the GDSFT for this population? A.0.66 B.0.71 C.0.81 D.0.84 •

D.0.84 Negative Predictive Value = NPV = true negative / all who test negative NPV = d/(c + d) = 105/125 = .84 or 84%

13. A test for celiac disease is being evaluated. It is called the GLUTINO test. Five hundred people are given both the GLUTINO test and a small bowel biopsy. The small bowel biopsy is felt to be the gold standard for the diagnosis of celiac disease. One hundred people had a positive GLUTINO test, the rest tested negative. Of the one hundred people with a positive GLUTINO test, 90 also had a positive small bowel biopsy. Of the 400 with a negative GLUTINO test, 350 had a negative small bowel biopsy. What is the Specificity of the Glutino test based on this study? A.0.64 B.0.88 C.0.90 D.0.97 •

D.0.97 Specificity = Sp = true negative / all without disease = d/(b + d) = 350/360 = .97

D.57% Sensitivity = true positive / (all those with disease) = a/(a+c) = 200/350 = .57 or 57%

A triple-blinded, randomized controlled clinical trial evaluated the potential benefits from the use of aspirin. Two thousand men who were cancer free and between the ages of 40 and 60-years were enrolled in the study. Half were randomly assigned to daily aspirin use and half were randomly assigned to placebo. The men were followed for 20 years and evaluated for the development of colon cancer. Fifty people in the treatment group developed colon cancer and 200 in the control group developed colon cancer. An evaluation of harm was also undertaken. Four hundred in the treatment group experienced a Gastrointestinal (GI) bleed. Two hundred in the control group experienced a GI bleed. 3. Based on this study approximately how many men would need to be treated with aspirin to prevent one case of colon cancer? • A.2 B.4 C.5 D.7 E.20

D.7 NNT = 1/ARR = 1/.15 = 6.667 = approximately 7

16. A test for rotavirus has the following properties when applied to a population with a prevalence of 35%. Sensitivity is 86%, Specificity is 75%, Positive Predictive Value (PPV) is 75% and Negative Predictive Value (NPV) is 92%. When this test is applied to a population at a school where there is prevalence of rotavirus of 50%, how would you expect the test properties to change? A.Increase in sensitivity, no change in specificity, PPV or NPV. B.Increase in sensitivity and PPV and no change in Specificity or NPV. C.Increase in sensitivity, decrease in specificity and no change in PPV or NPV. D.Increase in PPV, decrease in NPV and no change in Specificity or Sensitivity. E.Increase in PPV and NPV and no change in Specificity or Sensitivity •

D.Increase in PPV, decrease in NPV and no change in Specificity or Sensitivity. Sensitivity and Specificity are TEST properties. These can be printed on the testing kit - they do not vary with the Prevalence of disease. I did calculations to show this is the right answer (D). However, you do not have to do the calculations to know the answer. PPV and NPV DO VARY with the prevalence of disease. If you have a higher prevalence of disease you will have an increase in your positive predictive value and a decrease in your negative predictive value. If you have a lower prevalence of disease you will have a decrease in your positive predictive value and an increase in your negative predictive value. THE PREVALENCE DOES NOT AFFECT SENSITIVITY OR SPECIFICITY OF A TEST.

6. A case-control study may have a particular advantage over a cohort study when evaluating ______ disease. A.a fatal B.an indolent C.an infectious D.a rare E.a virulent

D.a rare For a rare disease it is unlikely you will be able to find a large cohort group to follow. Instead, you can identify the cases and look back to look at potential exposures and risk factors. You can only calculate the ODDS ratio you can not determine absolute risk of a disease using a case-control study. Cases and controls are assembled and then questioned (or records reviewed) to determine past exposure to risk factors. Participants in the case-control studies are chosen specifically from groups with and without the disease of interest. Good for RARE diseases (prevalence < 1%)

1. The true value of Mr. Smith's weight is 185 pounds. His bathrooms scale measures his weight to be 195 pounds. Concerned about potential weight gain he steps on and off of his scale 10 times and gets the following readings. 195 lbs, 196 lbs, 195 lbs, 195.5 lbs, 195 lbs, 195 lbs, 195.5 lbs, 196 lbs, 195.5 lbs and 196 lbs. The readings from this scale are ______________. A.accurate but not precise B.both accurate and precise C.neither accurate nor precise D.precise but not accurate

D.precise but not accurate

50 people with disease called "boy this is rare" (btir) are enrolled. 150 "controls" who don't have the btir disease are enrolled. All are interviewed about exposure to rubber ducks in their childhood. 40 of the cases were exposed to rubber ducks. 25 of the controls were exposed to rubber ducks. What is the most appropriate measure of association and what is the value of this measure? a)Relative Risk and the value is 8.8 b)Relative Risk and the value is .2 c)Relative Risk and the value is 20 d)Odds Ratio and the value is .2 e)Odds Ratio and the value is 4 f)Odds Ratio and the value is 20 •

F Odds Ratio and the value is 20

}The fictional town of Wyle Wyoming has a population of 500,000 people. Evidence shows there are 200 new cases of Diabetes in this town each year. In a given year there are 2,000 people who already have Diabetes. In this town there are 50 deaths from Diabetes each year. There are 200 deaths from all causes. No one moves to this town or moves away. }What is the incidence of Diabetes in Wyle Wyoming? } A.2,200/500,000 B.2,000/499,950 C.200/500,000 D.200/499,950 E.200/498,000 }

E.200/498,000 The Incidence is the number of NEW CASES over the people in the population who are AT RISK for the disease. With a total population of 500,000 and with 2,000 people who already have Diabetes, the number of people at risk is 500,000 - 2,000 = 498,000 people. The death information is thrown in to confuse you about this!

E.67% PPV = (true positive)/(all who test positive) = a/(a + b) = 200/300 = .6667 or 67%

20. The ability of a test to exclude a disease when the disease is absent is defined as the ____________. A.accuracy B.negative predictive value C.positive predictive value D.sensitivity E.specificity •

E.specificity Specificity is the ability of a test to indicate nondisease when no disease is present. I think of this as, we want the test to be specific for the disease we are looking for. We don't want to "capture" those without the disease.

A new test for Diabetes (DM) is developed that does not require a blood sample. It is called the NBDM test. To evaluate the test, 1000 patients were enrolled who all had some risk factor for DM. All received the NBDM test and also a fasting plasma glucose (gold standard) for diagnosis of DM. The NBDM was positive in 450 patients. Of the 450 patients with a positive NBDM, the fasting plasma glucose indicated DM in 400. Of the 550 with a negative NBDM, the fasting plasma glucose indicated DM in 40. = In the example of the test for DM, what would you answer if the question asked: • "What is the probability that a patient in this study who has a positive NBDM test actually has Diabetes?" •"What is the probability that a patient in this study who has a negative NBDM test, actually does not have Diabetes?"

In the example of the test for DM, what would you answer if the question asked, •"What is the probability that a patient in this study who has a positive NBDM test actually has Diabetes?" This is the same thing as the positive predictive value. It would be 89% •What is the probability that a patient in this study who has a negative NBDM test, actually does not have Diabetes? This is the same as the negative predictive value. It would be 93%. •

•Researchers wished to investigate the potential relationship between soccer playing when young and ACL tears in girls and young women. They enrolled 200 girls who played soccer and were between the ages of 8 and 10. They also enrolled 200 girls who were between the ages of 8 and 10 but who did not play soccer. All of the girls were followed for 10 years. The girls were interviewed yearly, medical and surgical histories were recorded. Specifically they determined if there was a history of an ACL tear. Fifty of the soccer players developed an ACL tear and 20 of those who did not play soccer at enrollment developed an ACL tear. •What is the risk of ACL tear among the soccer players?

The risk of ACL tear among the soccer players is .25 = 50/200

•A clinical trial was done with patients who had (1) suffered at least two recurrences of duodenal ulcers, (2) were currently in remission, and (3) tested positive for the presence of H. pylori. Participants were divided randomly into two groups. One group received a common ulcer medication; the other group received the same medication plus an antibiotic. Patients were followed for 1 year and were checked to see if the ulcer recurred (yes/no) during the 12-month observation period. The data appear in the table on the next slide. ulcer + ab; 9 / 99 ulcer; 89/ 15 a) Is the calculation of the odds ratio or relative risk more appropriate for these data? Why? b) Calculate the cumulative incidence of ulcer recurrence in each group of patients. c) Compute the measure of association you chose from part a. d) The investigators contend that the combination of ulcer medication plus antibiotics virtually eliminated ulcer recurrence. Do you agree? Why or why not?

a) Is the calculation of the odds ratio or relative risk more appropriate for these data? Why? Relative Risk, the patients were followed over time. b) Calculate the cumulative incidence of ulcer recurrence in each group of patients. Treatment group (Ulcer Rx plus Abx) = 8% and control group (Ulcer Rx only) = 86% c) Compute the measure of association you chose from part a. RR = .097 (Can you say this in words?) d) The investigators contend that the combination of ulcer medication plus antibiotics virtually eliminated ulcer recurrence. Do you agree? Why or why not? •The Relative Risk of ulcer recurrence in those treated with ulcer medication plus antibiotics compared with those treated with ulcer medication alone was .097. This says that those treated with the combination had approximately one-tenth the rate of ulcer recurrence compared with those treated with the ulcer medication alone.

a)0.20 ARR = risk in the unexposed - risk in those exposed to acai = 300/1000 - 100/1000 = .3 - .1 = .2 Those who were not exposed to the new treatment had the higher rate, the treatment reduced the rate of development of hypertension.

A new test for Diabetes (DM) is developed that does not require a blood sample. It is called the NBDM test. To evaluate the test, 1000 patients were enrolled who all had some risk factor for DM. All received the NBDM test and also a fasting plasma glucose (gold standard) for diagnosis of DM. The NBDM was positive in 450 patients. Of the 450 patients with a positive NBDM, the fasting plasma glucose indicated DM in 400. Of the 550 with a negative NBDM, the fasting plasma glucose indicated DM in 40. What is the positive predictive value of the NBDM in this population? a)89% b)90% c)91% d)92% e)93%

a)89% Create 2x2 table. PPV = true positive/all who test positive = a/(a+b) = 400/450 = .88888 so approximately 89%

a)99% •Sn = .95, Sp = .98, Prior probability = .85 •Solve p(D+|T+) = (Sn)(Pr)/[(Sn)(Pr) + (1-sp)(1-Pr)] •= .95x.85/[(.95x.85) + (.02x.15) = .8075/.8105 = .996 or 99.6% •OR solve using a 2x2 table, calculate the PPV = a/(a + b)

Researchers wish to study the relationship between stroke in women at a young age (defined as under age 50) and oral contraceptive (OCP) use. They enrolled 100 women who had a history of stroke occurring prior to age 50-years and 100 controls. The controls were women under age 50-years who had no history of stroke. All participants were interviewed and use of OCPs documented. What type of study is this? a)Case-control study b)Prospective cohort study c)Randomized controlled clinical trial d)Retrospective cohort study •

a)Case-control study The cases are those with the OUTCOME of stroke and the controls are matched people of similar age who did not have a history of the outcome "Stroke." This is not a prospective cohort study. The people are not followed forward over time. Also, in a cohort study (of any type) the groups are established based on EXPOSURE and not based on the OUTCOME or DISEASE. This is not a randomized controlled clinical trial - there is no intervention or randomization. This is not a retrospective cohort study. In all cohort studies the first objective is to establish two groups the EXPOSED and the NON-EXPOSED. In this example the groups are based on the OUTCOME and they are then asked about the exposure.

A 55-year-old man has multiple asymptomatic gallstones. He can either have surgery now to remove them or he can wait for symptoms. If he has surgery he has a 20% chance of moderate surgical complications and an 80% chance of complication free removal. If he waits he has a 10% chance of severe complications and a 90% chance of mild symptoms. He ranks his utility values as follows: 0.6 moderate surgical complications, 1 for complication free removal, 0.2 for severe complications and 0.8 for mild symptoms. Should he operate or wait? a)Operate b)Wait

a)Operate Utility from operation now = .2x.6 = .8x1 = .12 + .8 = .92 Utility from waiting = .1x.2 + .9x.8 = .02 + .72 = .74 Higher utility from operating now.

Researchers wish to study the risk of insomnia development in medical students compared with other students. They enroll 500 medical students from various universities to serve as cases and 1000 graduate students from various universities to serve as controls. Students were all followed for 4 years and interviewed regarding multiple aspects of their health and wellbeing - including insomnia. After 4 years, 400 medical students were found to have developed insomnia and 500 graduate students developed insomnia. What is the most appropriate measure of association and what is the value of this measure? a)Relative Risk and the value is .8 b)Relative Risk and the value is 1.6 c)Relative Risk and the value is 4 d)Odds Ratio and the value is .8 e)Odds Ratio and the value is 1.6 f)Odds Ratio and the value is 4

a)Relative Risk and the value is 1.6

50 people with disease called "boy this is rare" (btir) are enrolled. 150 "controls" who don't have the btir disease are enrolled. All are interviewed about exposure to rubber ducks in their childhood. 40 of the cases were exposed to rubber ducks. 25 of the controls were exposed to rubber ducks. What type of study is this (besides a silly one)? a)case control study b)field trial c)prospective cohort study d) randomized controlled clinical trial •

a)case control study

10) An 80 year-old man is found to have a tumor. If operated on now he will either die on the table or live another 10 years pain free. If he has surgery now he has a 20% chance of dying on the table and an 80% chance of living 10 years pain free. If he chooses to not have surgery he will either die in two years or he will live another 10 years with some mild pain. Without surgery he has a 30% chance of dying in 2 years and a 70% chance of living another 10 years with some mild pain. He places utility values of 0 on dying now, 1 on living pain free for 10 years, .2 of dying in 2 years and .6 of living 10 years in some pain. Using the data given, his utility is maximized by: a.choosing surgery now b.choosing to avoiding surgery c.This can not be calculated using the data given • •

a.choosing surgery now •Utility of surgery now is .2 * 0 + .8 x 1 = .8 • (note you can calculate the .8 as 1-.2, he will either die on the table or live 10 years). He has a .2 probability of death on the table and a .8 probability of living 10 years. In this example I gave you both the .8 and the .2, often you will just get one probability and have to know they sum to 100% or 1.0 •The utility of "no surgery" is .3 * .2 + .7 * .6 = .06 + .42 = .48 •His expected utility is higher if he has surgery now. •

3) In Bayes Theorem p(D - | T- ) can be called the ________________. a)Positive predictive value b)Negative predictive value c)Prevalence d)Probability of disease given a negative test e)Probability of not having disease at all

b)Negative predictive value

Researchers wish to study the impact of chewing tobacco on the development of oral cancer. Researchers identified a group of people between the ages of 20 and 40-years-old and determined who chewed tobacco and who did not. One-hundred people who chewed tobacco were enrolled and 200 who did not chew tobacco were enrolled. The people were followed for 20 years to determine who developed an oral cancer. Fifty of the tobacco chewers developed an oral cancer and 30 of the non-tobacco-chewers developed an oral cancer. What is the attributable risk of oral cancer from chewing tobacco, according to this study? •What type of study was that on previous slide? a)Case-control b)Prospective cohort study c)Retrospective cohort study •What is the most appropriate measure of association for that study and what is the value of that measure? a)Odds ratio value is 0.85 b)Odds ratio value is 1.67 c)Relative risk value is 0.5 d)Relative risk value is 3.3

b)Prospective cohort study d)Relative risk value is 3.3

•Meta-analysis can be used most effectively when ______________. a.the results from qualitative research are uncertain. b.there are results available from a number of small randomized clinical trials (with small sample sizes). c.there are results available from multiple large randomized clinical trials (with large sample sizes). d. there are results available from a few small case control studies and these are combined with small randomized clinical trials. •

b.there are results available from a number of small randomized clinical trials (with small sample sizes). •Meta-analysis is generally done with quantitative, not qualitative research. •When there are results available from a number of large RCTs, meta-analysis is not needed. •Case-control results can not be combined with RCT results. Case-control studies do not show causation. •

c)22% •Assume population of 100 •Calculate all those with disease = Pr x Pop = .85 x 100 = 85 (this is a + c) •Solve for cell a using Sn = a/(a + c) = .95 .95 = a / (85), a = .95 x 85 = 80.75 •Fill in cell a, since you now know a and (a + c) you can solve for c = 85 - 80.75 = 4.25 •Solve for total of (d + b) = 100 - (a + b) = 100 - 85 = 15 •Solve for cell d using Sp = d/(b + d) = .98 .98 = d/15, d = .98 x 15 = 14.7 •Solve for cell b = (b + d) - d = 15 - 14.7 = .3 •NPV = d/(c + d) = 14.7/(4.25+14.7) = .775 •PPV = a/(a + b) = 80.75/(80.75+.3) = .996 •To answer the question asked for # 5 take 1 - NPV

In the acai supplement study 1,000 people received acai and 1,000 received placebo. There were 200 people in the treatment group who experienced daily nausea and 50 in the control group who experienced daily nausea. After treating how many people with acai would you expect to cause one case of daily nausea? a)4.5 b)5.6 c)6.7 d)7.8

c)6.7 NNH = 1/ARI ARI = risk in exposed - risk in unexposed = 200/1000 - 50/1000 = .2 - .05 - .15 1/.15 = 6.66666 or 6.67

•A 10-year-old boy presents with sore throat and fever. He has posterior pharyngeal exudate. You estimate his pre-test probability of strep throat is 60%. You perform a rapid strep test to look for "strep throat". The sensitivity of the rapid strep test is 95% and the specificity is 92%. What is the probability that he has strep throat if the rapid strep test is positive? a)90% b)92% c)95% d)98%

c)95% This is the positive predictive value. It is purely coincidence here that it is equal to the sensitivity of the test. PPV = a/(a+b) = 57/60.2 = .946 or 95%

•A 9 year-old boy presents with a sore throat, headache and stomach upset. He has a temperature of 99.8 F, swollen glands and thick white tonsillar exudate. Other children from his 3rd grade class have been diagnosed with strep throat. You estimate the probability of strep based on the history and physical is 85%. A rapid strep test available in your office has a Sensitivity of 95% and a Specificity of 98% 6) The strep test came back positive. The boy's parents feel strongly that antibiotics should not be used unless there is a "firm diagnosis." What is the best next step? a)Repeat the rapid strep test, treat only if positive. b)Send out a confirmatory culture and only treat if it is positive. c)Counsel the parents no further testing is indicated and treat now. d)Send the patient home to see if symptoms progress. e)Prescribe a "mild" antibiotic to use for a shorter than standard duration. •

c)Counsel the parents no further testing is indicated and treat now. •The posterior probability of strep is over 99%. This is as confirmed as you will get. There is no value in repeating the test. You don't want to wait for a culture or worsening symptoms. You never want to give an inadequate antibiotic prescription. •

2) In Bayes theorem, in the equation that equals p(D+ | T+) the numerator represents _________________ a)True negatives b)All negatives c)True positives d)All positives e)Prevalence •

c)True positives

Researchers wish to study the risk of insomnia development in medical students compared with other students. They enroll 500 medical students from various universities to serve as cases and 1000 graduate students from various universities to serve as controls. Students were all followed for 4 years and interviewed regarding multiple aspects of their health and wellbeing - including insomnia. After 4 years, 400 medical students were found to have developed insomnia and 500 graduate students developed insomnia. This is an example of a _____________. a)case control study b)field trial c)prospective cohort study d) randomized controlled clinical trial

c)prospective cohort study

Prior to the start of the screening program, a new test for Parkinson's disease is released. This test has a Sensitivity of 98% and a Specificity of 98%. 100,000 people will be screened. The prevalence of Parkinson's disease in the population that will be screened is 0.1%. 8) How many people in this population have Parkinson's disease? a.1 b.10 c.100 d.1,000 e.10,000 •

c.100

7) Four tests are being evaluated to screen for early Parkinson's disease. They will each diagnose the disease before any clinical symptoms. The test characteristics are listed. In what order should these tests be applied? Test A Sn = 80% Sp = 95% Test B Sn = 95% Sp = 90% Test C Sn = 99% Sp = 92% Test D Sn = 96% Sp = 98% a.Test C, followed by test A if C is positive b.Test C, followed by test D if C is negative c.Test C, followed by test D if C is positive d.Test B, followed by test C if B is negative e.Test D, followed by test C if D is positive •

c.Test C, followed by test D if C is positive •The take home point here is you want to do the most sensitive test as the screening test and then the most specific test as the confirmatory test. •The confirmatory test is used on only those who tested POSITIVE with the screening test. •A highly sensitive test, one that is a good screening test, will have a low false-negative rate. When you screen you don't want to "miss" those with disease, you don't want false negatives. Sensitivity = a / (a + c) = true positives/all with disease •A highly specific test will have a low false positive rate. These are good confirmatory tests when you want to be sure that those who you say have the disease, really do. Specificity = d/(b + d) = true negatives/all without disease

d)5 NNT = 1/ARR = 1/.2 = 5

A new test for osteoporosis is released. The test has a sensitivity of 90% and a specificity of 80%. The prevalence osteoporosis in the population is 30%. A screening program is set up for 1,000 people. What is the probability that a person in this population does not have osteoporosis if the screening test is negative. a)66% b)80% c)90% d)95%

d)95% NPV = d/(c+d) = 560/590 = .949 or 95%

1) In Bayes theorem, in the equations that equals p(D+ | T+), the denominator represents ____________ a)True negatives b)All negatives c)True positives d)All positives e)Prevalence •

d)All positives

Prior to the start of the screening program, a new test for Parkinson's disease is released. This test has a Sensitivity of 98% and a Specificity of 98%. 100,000 people will be screened. The prevalence of Parkinson's disease in the population that will be screened is 0.1%. 9) The prior probability of disease before screening and the posterior probability of disease after a positive test are _____, ________. a)0.1, .845 b).001, .052 c)0.1, .047 d).01, .033 e).001, .047 •

e).001, .047 •Use either a 2x2 or use the test properties. The prior probability is the prevalence, this is .1% = .001. •The posterior probability after a positive test is found with Bayes Theorem, this is the PPV •.98*.001=.00098 = Sn * Pr •.02*.999=.01998 = (1-Sp) (1-Pr) •.00098/(.00098+.01998)=.00098/.02096 = .04675 = .047 •Now try on your own using a 2x2 table! •

6. A randomized-controlled clinical trial evaluated a new medication with dosages 10mg, 20mg and 30mg. They found an increase in HDL cholesterol levels in patients taking the study drug. The researchers noticed that there were greater increases in HDL cholesterol in those on 30mg of study drug compared with those on 10mg of study drug. This suggests _____________. }A. a dose-response }B. consistency }C. biologic plausibility }D. specificity }

}A. a dose-response\ Notice that with higher doses of the study drug there are greater increases in HDL cholesterol. This suggests the study drug affects HDL cholesterol

}7. A triple blind randomized controlled clinical trial studied a drug "X" for the treatment of Diabetes. Researcher found that people taking study drug X had greater improvements in hemoglobin A1C than did people on the control drug "Y." The study was free from bias but did have random error. This random error likely }A. over-estimated the benefit of drug X }B. under-estimated the benefit of drug X }C. did not affect the magnitude of the benefit of drug X.

}C. did not affect the magnitude of the benefit of drug X. Random error is non-differential error, it produces findings that are too high or too low in approximately equal amounts. This is less serious than bias because random error is less likely to distort the study findings.

4. A recent research study found higher levels of BPA in urine from obese children than non-obese children. This demonstrates __________. }A. a causal link between BPA and obesity. }B. a good example of recall bias. }C. a definite example of confounding. }D. an association between BPA and obesity. }E. an example of irresponsible research. }

}D. an association between BPA and obesity. This study showed an association but did not demonstrate causation.

5. Mothers of severely pre-mature infants and mothers of full term infants are interviewed. The mothers are asked about 'risk factors' and behaviors during their pregnancy. This study design poses the risk for __________. }A. allocation bias }B. measurement bias }C. non-differential error }D. recall bias }E. selection bias

}D. recall bias

3. Researchers are evaluating the effect of diet and exercise on weight loss compared with a new weight loss medication. Volunteers for the study are solicited using the local newspaper. Volunteers choose whether to be in the diet and exercise group or in the weight loss medication group. This study design allows for _______ bias. }A. allocation }B. measurement }C. recall }D. selection

}D. selection This is selection bias, the volunteers self select what group to join (diet and exercise or medication).

1. If factor A is present then the disease X will always occur. Factor A is ________ for the disease X. }A. a confounder }B. a risk factor }C. an effect modifier }D. the sufficient cause }E. the necessary cause

}D. the sufficient cause This is straight from the definition of a sufficient cause.

2.It has been observed that people who carry matches have higher rates of lung cancer. It must then be true that carrying matches ● ● §A. causes lung cancer. §B. is associated with lung cancer. §C. is a sufficient cause for lung cancer. §D. is a necessary cause for lung cancer. §

§B. is associated with lung cancer. All you can say is what is observed, this does not prove causation.

•Researchers wished to investigate the potential relationship between soccer playing when young and ACL tears in girls and young women. They enrolled 200 girls who played soccer and were between the ages of 8 and 10. They also enrolled 200 girls who were between the ages of 8 and 10 but who did not play soccer. All of the girls were followed for 10 years. The girls were interviewed yearly, medical and surgical histories were recorded. Specifically they determined if there was a history of an ACL tear. Fifty of the soccer players developed an ACL tear and 20 of those who did not play soccer at enrollment developed an ACL tear. •What is the most appropriate measure of association and what is the value of this measure? •

•Answer: Relative Risk value = 2.5

2. In clinical research, the exposures or the risk factors being studied are termed the • •A) dependent variables •B) independent variables

•B) independent variables The outcome is the Dependent variable.

preview q Item 7: A report of a large therapy trial documents that the absolute risk reduction over one year for herpes with a new protective gel was 10%. What is the Number Necessary to Treat (NNT) to prevent one case over one year? •A. 1 •B. 9 •C. 10 •D. 99 •E. 100

•C. 10 Number needed to treat = 1 / absolute risk reduction NNT = 1 / .1 = 10

?? •Maybe the question stem will tell you the rate instead of the number in each arm of the trial and the number with the outcome. •For example, study results might be given that show 50% of people in the treatment group with drug X have a bad side-effect and 10% of people in the control group with placebo have the same bad side-effect. After treating how many people with drug X would you expect to see the bad side effect?

•Maybe the question stem will tell you the rate instead of the number in each arm of the trial and the number with the outcome. •For example, study results might be given that show 50% of people in the treatment group with drug X have a bad side-effect and 10% of people in the control group with placebo have the same bad side-effect. After treating how many people with drug X would you expect to see the bad side effect? ARI = 0.5 - 0.1 = 0.4, the NNH = 1/.4 = 2.5, the answer is 2.5 people.

A new test for Diabetes (DM) is developed that does not require a blood sample. It is called the NBDM test. To evaluate the test, 1000 patients were enrolled who all had some risk factor for DM. All received the NBDM test and also a fasting plasma glucose (gold standard) for diagnosis of DM. The NBDM was positive in 450 patients. Of the 450 patients with a positive NBDM, the fasting plasma glucose indicated DM in 400. Of the 550 with a negative NBDM, the fasting plasma glucose indicated DM in 40. = a) 89 b)90% c)91% d)92% e)93% •Sensitivity (Sn) •Specificity (Sp) •Negative Predictive Value (NPV) •Prevalence of DM in this sample population (Pr)

•Sensitivity (Sn) = 91% •Specificity (Sp) = 91% •Negative Predictive Value (NPV) = 93% •Prevalence of DM in this sample population (Pr) = 44 % •

•Researchers wish to study a new antibiotic (X) to treat community acquired pneumonia (CAP). Five hundred patients with CAP were enrolled in the study. Those enrolled were randomly assigned to the treatment group with drug X or the control group with standard therapy. Half were assigned to each group. They were evaluated for full recovery within one week of treatment. In the study group 150 recovered within one week. In the control group 50 recovered within one week. •What is the full recovery rate for those in the treatment group? •What is the full recovery rate for those in the control group? •What is the improvement of the recovery rate that might be attributed to the new treatment (the rate difference)?

•What is the full recovery rate for those in the treatment group? .60 or 60% •What is the full recovery rate for those in the control group? .20 or 20% •What is the improvement of the recovery rate that might be attributed to the new treatment? .60 - .20 = .40

•Researchers wished to investigate the potential relationship between soccer playing when young and ACL tears in girls and young women. They enrolled 200 girls who played soccer and were between the ages of 8 and 10. They also enrolled 200 girls who were between the ages of 8 and 10 but who did not play soccer. All of the girls were followed for 10 years. The girls were interviewed yearly, medical and surgical histories were recorded. Specifically they determined if there was a history of an ACL tear. Fifty of the soccer players developed an ACL tear and 20 of those who did not play soccer at enrollment developed an ACL tear. •What is the risk of ACL tear among those who didn't play soccer? •What is the increase in risk of ACL tear related to soccer playing?

•What is the risk of ACL tear among those who didn't play soccer? Answer is .10 = 20/200 •What is the increase in risk of ACL tear related to soccer playing? Answer is .25 - .10 = .15 = Risk difference

A randomized controlled clinical trial evaluated the potential benefits of acai supplements. Two thousand people were enrolled and half were randomly assigned to acai supplement and half to placebo. The people were evaluated for the development of hypertension. One hundred in the treatment group and three hundred in the control group developed hypertension. How many people will need to be treated with acai supplements in order to prevent one case of hypertension? •What type of study was the acai study? •What is the relative risk reduction in the risk for hypertension from treatment with acai? •What is the relative risk of hypertension in those treated with acai compared to those treated with placebo? •What is the risk for hypertension in those treated with acai?

•What type of study was the acai study? Randomized controlled clinical trial. •What is the relative risk reduction in the risk for hypertension from treatment with acai? The RRR = .67 •What is the relative risk of hypertension in those treated with acai compared to those treated with placebo? The RR = .33 What is the risk for hypertension in those treated with acai? The risk in those treated with acai = 0.1

epi 456

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