BIOSTATS final

23. After a new antidepressant has been on the market for 5 years , it is determined that of 2,000 people who have taken the drug , 400 complained of persistent nausea . If a physician has two patients on this antidepressant , the probability that both of them will experience persistent nausea is approximately ( A ) 4 % ( B ) 8 % ( C ) 24 % ( D ) 40 % ( E ) 64 %

( A ) 4 % The probability of both patients ( A and B ) taking this antidepressant experienc ing nausea equals the probability of A experiencing nausea ( 400 / 2,000 = 0.2 ) times the probabil ity of B experiencing nausea ( 400 / 2,000 = 0.2 ) = 0.2 x 0.2 = 0.04 , that is , about 4 % .

Questions 10-13 A patient is given a new screening test for tuberculosis . Although the patient is infected , the test indicates that the patient is well . 10. This test result is known as 11. To identify all patients infected with tuber culosis , the cutoff point for this test should be set at the point of highest 12. If this new screening test has a sensitivity of 90 % and a specificity of 70 % in a group of young Russian prisoners in which the prevalence of tuberculosis is 50 % , the positive predictive value of this test is best estimated as 13. If the test is given only to elderly prison ers in whom the incidence and prevalence of tuberculosis is higher than in young prisoners the positive predictive value and sensitivity of this screening test will , respectively , change in which of the following ways ? ( A ) false negative sensitivity 75 % Positive Predictive Value increased Sensitivity not changed ( B ) false positive accuracy ydada ( C ) true positive ppv yada ( D ) true negative npv yada ( E ) predicitve specificity yada

( A ) false negative sensitivity 75 % Positive Predictive Value increased Sensitivity not changedfalse negative result occurs are people if a oest does not detect tuberculosis in someone who truly is infected . True post ewell people whom a test has correctly identified as being well . False positives are well people whom atest has incerectly identified as being ill . In order to identify all truly infected people ( TP and FN ) the point for the test should be set at the point of highest sensitivity that is the point at which there are the first number of FN . Using the data provided and assuming there are a total of 200 young prisoners , the positive predictive value ( IP / IP + ) of this sest is 90/90 30 79 % . Calculations shown below indicate that if prevalence of the disease is increased in a population ( e.p elderly men ) , positive predictive value increases , ber sensitivity does not change If the prevalence of the disease is increased , both TP and FN will increase to the same esien and sensitivity will not change . However , with increased prevalence , TP will increase and FP will decrease so posidve predictive value will increase . Also , because with increased prevalence , IN increases but TN decreases , negative predictive value will decrease

23. A randomized controlled trial is conducted to assess the risk for development of gastrointestinal adverse effects using azithromycin compared with erythromycin in the treatment of pertussis in children . Of the 100 children with pertussis enrolled , 50 receive azithromycin , and 50 receive erythromycin . Results show vomiting among 5 patients in the azithromycin group , compared with 15 patients in the erythromycin group . Which of the following best represents the absolute risk reduction for vomiting among patients in the azithromycin group ? ( A ) 0.1 ( B ) 0.2 ( C ) 0.33 ( D ) 0.67 ( E ) 0.8

( B ) 0.2 The absolute risk reduction

29. A study is conducted to assess the useful ness of a new screening test to detect bacterial meningitis caused by Streptococcus pneu moniae infection . The infection has a high mor tality rate if it is not identified early . However , rapid administration of a broad - spectrum antibiotic such as cephalosporin significantly decreases the mortality rate with minimal risks . A total of 200 emergency room patients with classic meningitis symptoms such as fever and neck stiffness are assessed with the new test . This graph shows the distribution of infected and noninfected participants according to the results of the test . Which lettered point is the optimal diagnostic cutoff point for the result of this test ? ( A ) A ( B ) B ( C ) C ( D ) D ( E ) E

( B ) B Because bacterial meningitis has a high mortality rate and because the treat ment has minimal risks , it is important to identify and treat anyone who might be infected . Anyone with a positive test ( above cutoff point B ) should therefore be treated with the antibiotic even if they may be a false positive .

22. A study is designed to evaluate the feasibility of acupuncture in children with chronic headaches . Sixty children with chronic headaches are recruited for the study . In addition to their usual therapy , all children are treated with acupuncture three times a week for 2 months . Which of the following best describes this study design ? ( A ) Case - control ( B ) Case series ( C ) Crossover ( D ) Cross - sectional ( E ) Historical cohort . ( F ) Randomized clinical trial

( B ) Case series There is treatment involved but no randomization in the selection of subjects .

27. A new laboratory test to detect osteoporo sis in women greater than 80 years of age has a sensitivity of 90 % and a specificity of 75 % . Autopsy studies suggest that osteoporosis has a prevalence of 30 % for women in this age group . Using this information , the likelihood that a woman with a positive test actually has osteo porosis is best estimated as ( A ) 12.5 % ( B ) 30 % ( C ) 60 % ( D ) 70 % ( E ) 85 %

( C ) 60 % Assuming a total of 1,000 women over age 80 years and a prevalence rate of 30 in this age group , 300 women have osteoporosis and 700 are well . Of the 300 who have osteopo rosis , a screening test with a sensitivity of 90 % would identify 270 TP and 30 FN . Of the 700 who are well , a screening test with a specificity of 75 % would identify 525 TN and 175 FP Using these data ( see table below ) , the likelihood that a woman with a positive test actually has osteoporosis ( positive predictive value ( TP / TP + FP ) is 270 / 270 + 175-60 %

21. Over 1 year , a study is conducted to assess the antileukemic activity of a new tyrosine kinase inhibitor in patients with chronic myeloid leukemia in blast crisis . All patients enrolled in the study are informed that they would be treated with the tyrosine kinase inhibitor . They are assigned to successive dose cohorts of 300 to 1000 mg / day of the drug . Six to eight patients are assigned to each dose . Treatment efficacy is determined based on the results of complete blood counts and bone marrow assessments conducted regularly throughout the study . study is best described as which of the following ? ( A ) Case - control study ( B ) Crossover study ( C ) Open - labeled clinical trial ( D ) Randomized clinical trial ( E ) Single - blind , randomized , controlled trial

( C ) Open - labeled clinical trial There is treatment but no randomization of subjects .

6. A study is designed to determine the rela tionship between emotional stress and peptic ulcer . To do this , the researchers use hospital records of patients diagnosed with peptic ulcer disease and patients diagnosed with other disorders over the period from July 2009 to July 2019. The emotional stress each patient was exposed to was determined from these records and was then quantified a score of 1 ( least stress ) to 100 ( most stress ) . This study is best described as a ( A ) cohort study ( B ) cross - sectional study ( C ) case - control study ( D ) historical cohort study ( E ) clinical treatment trial

( C ) case - control study Case - control studies begin with the identification of subjects who have specific disorder cases , i.e. , ulcer patients ) and subjects who do not have that disorder ( con trols , i.e. , those diagnosed with other disorders ) . Information on the prior exposure of cases and controls to risk factors is then obtained . In this case - control study , the investigators used cases ( ulcer patients ) and controls ( patients with other disorders ) and looked into their histories ( hospital records ) to determine the occurrence of and quantify the level of the risk factor ( i.e. , emotional stress ) in each group . Cohort studies begin with the identification of specific popula tions ( cohorts ) , who are free of illness at the start of the study and can be prospective ( taking place in the present time ) or historical ( some activities have taken place in the past ) . Clinical treatment trials are cohort studies in which members of a cohort with a specific illness are given one treatment and other members of the cohort are given another treatment or a placebo . The results of the two treatments are then compared . Cross - sectional studies involve the collection information on a disease and risk factors in a

20. A new blood test to detect prostate cancer is evaluated in 300 male volunteers . A needle biopsy of the prostate gland is done on all men with serum prostate - specific antigen concentrations greater than 5 ng / mL ( N less than 4 ) .One hundred men undergo biopsy procedures ; 90 are found to have prostate cancer , and five are found to have chronic prostatitis . Which of the following is necessary to calculate the sensitivity of this test ? ( A ) Incidence of chronic prostatitis in the general population ( B ) Number of men with test results greater than 5 ng / mL and a normal biopsy specimen ( C ) Prevalence of chronic prostatitis in the general population ( D ) Prostate biopsies of men with test results equal to or below 5 ng / mL

( D ) Prostate biopsies of men with test results equal to or below 5 ng / mL . Those who underwent biopsy were from the group with serum prostate specific antigen concentrations greater than 5 ng / mL . Some men with antigen concentrations less than 5 ng / mL may well have prostate cancer .

24. In a cohort study of elderly women , the relative risk ratio for hip fractures among those who exercise regularly is 1.2 ( 95 % confidence interval of 1.1 to 1.8 ) . Which of the following is the most appropriate conclusion about the effect of regular exercise on the risk for hip fracture ? ( A ) Statistically nonsignificant increase in risk ( B ) Statistically nonsignificant overall decrease in risk ( C ) Statistically significant overall decrease in risk ( D ) Statistically significant overall increase in risk

( D ) Statistically significant overall increase in risk Women who are exposed to the risk factor are 1.2 times more likely to have hip fractures than those not exposed . This 1.2 falls within the 95 % confidence interval shown .

14. A case - control study is done to determine if elderly patients who have dementia are more likely to be injured at home than elderly patients who do not have dementia . The results of the study show an odds ratio of 3. This figure means that if an elderly patient was injured at home , that patient ( A ) should be placed in an extended - care facility ( B ) was one - third more likely to have demen tia than a patient who was not injured at home ( C ) was no more likely to have dementia than a patient who was not injured at home ( D ) was three times more likely to have dementia than a patient who was not injured at home ( E ) should be kept at home

( D ) was three times more likely to have dementia than a patient who was not injured at home An odds ratio of 3 means that an elderly patient who was injured at home was three times more likely to have dementia than a patient who was not injured at home . This number does not indicate whether or not certain people should remain at home or be cared for by others .

26. A research study is done to determine if intravenous ( IV ) ibandronate sodium ( Boniva ) will decrease the incidence rate of hip fractures . in perimenopausal women . There are 2,600 women in the ibandronate sodium group , of whom 130 develop hip fractures . Of the 2,600 women in the placebo group , 260 develop hip fractures . Based on these data , how many women need to be treated with ibandronate sodium to prevent one hip fracture ? ( A ) 1 ( B ) 5 ( C ) 10 ( D ) 15 ( E ) 20

( E ) 20 Twenty women need to be treated with IV ibandronate sodium to prevent one hip fracture . The number needed to treat is calculated as 1 / absolute risk reduction of the 2,600 women in the placebo group , 260 develop hip fractures . Of the 2,600 women in the bandronate sodium group , 130 develop hip fractures . The incidence rate of hip fractures in the placebo group is therefore 260 / 2,600 ( 0.1 or 10 % ) and the incidence rate of hip fractures in the bandro nate sodium group is 130 / 2,500 ( 0.05 or 5 % ) . Therefore , absolute risk reduction ( ARR ) is 10 % 5 % 5 % . If 5 % of women were prevented from having a hip fracture by the drug , the NNT is 1.0 divided by 0.06 , or 20

1. A study is done to determine the effectiveness of a new antihistamine . To do this , 25 allergic patients are assigned to one of the two groups , the new drug ( 13 patients ) or a placebo ( 12 patients ) . The patients are then followed over a 6 - month period . This study is best described as a ( A ) cohort study ( B ) cross - sectional study ( C ) case - control study ( D ) historical cohort study ( E ) clinical treatment trial

( E ) clinical treatment trial This study is best described as a clinical treatment trial , a study in which a cohort receiving a new antihistamine is compared with a cohort receiving a placebo .

28. A study is done to determine the effective ness of a new antihistamine . To do this , 25 . allergic patients are assigned to one of the two groups , the new drug ( 13 patients ) or a placebo ( 12 patients ) . The patients are then followed over a 6 - month period . This study is best described as a ( A ) cohort study ( B ) cross - sectional study ( C ) case - control study ( D ) historical cohort study ( E ) clinical treatment trial

( E ) clinical treatment trial This study is best described as a clinical treatment trial , a study in which a cohort receiving a new antihistamine is compared with a cohort receiving a placebo .

7. An intelligence quotient ( IQ ) test has high interrater reliability . This means that ( A ) the test involves structured interviews ( B ) a new assessment strategy is being used ( C ) the test actually measures IQ and educational level ( D ) the results are very similar when the test is administered a second time ( E ) the results are very similar when the test is administered by a different examiner

( E ) the results are very similar when the test is administered by a different examiner Interrater reliability is a measure of how similar test findings are when used different examiners .

2. When treated with a certain drug , 35 % of patients with breast cancer survive . When provided with a placebo , 10 % of similar patients survive . is : A 4 B 5 C 10 D 35

A 4 The absolute risk reduction = 35 % - 10 % = 25 % NNT =

3. An education program designed to create awareness of rheumatic fever may be described as : A primary prevention B secondary prevention C tertiary prevention D immunity to rheumatic fever

A primary prevention See notes on prevention

11. A group of experts agree that the results of tests carried out on inmates at Her Majesty ' : Prison are consistent with diagnosis for tuberculosis . This is an example of : A face validity B content validity C construct validity D criterion validity

B content validity Take note of expert opinion

8. Sensitivity Which one of the following will decrease the sensitivity of the test ? A increase TP B increase FN C decrease FN D make TP = FN

B increase FN The value of a fraction decreases if only the denominator is increased

26. A study determines that the mean blood cholesterol level in 200 non - diabetic hospitalizes patients is 195 mg / dL and in 180 diabetic hospitalizes patients is 210 mg / dL . The probability that the observed difference is due to a chance is reported to be 5 % . There is also a 20 % probability of concluding that there is no difference in blood cholesterol level when there is one in reality . What is the power of the study ? A. 0.05 B. 0.20 C. 0.50 D. 0.80 E. 0.95

B. 0.20 the sentence "There is also a 20 % probability of concluding that there is no difference in blood cholesterol level when there is one in reality" is power

This type of study design has a washout period to allow for subjects to be unaware of treatment / placebo status . A. Randomized pre - post B. Cross - over C. Randomized post D. Cross - sectional E. Cohort

B. Cross - over

The three techniques used to increase statistical power are : A. Case control , ANOVA , and cross - sectional studies B. Repeated measures ANOVA , Factorial ANOVA , and ANCOVA C. ANCOVA , Factorial ANOVA , and MANOVA D. MANOVA , ANCOVA , and case control studies

B. Repeated ANOVA , factorial ANOVA , and ANCOVA

4. The Odds - ratio test is the appropriate test for evaluating risk in : A cohort studies B prospective studies C case / control studies D longitudinal studies

C case / control studies See notes on Odds ratio

15. A study was designed as follows : One hundred persons were randomly selected from a certain population . They were tested for hypertension and assigned to one of two groups : normal and hypertensive . They were followed for 10 years and the presence of heart disease was measured over that period . This is an example of a : A cross - over study B case / control study C prospective study D Spearman correlation study

C prospective study Note that heart disease is what is in focus here ; NOT hypertension

This type of study design assesses the burden of disease at a specific point in time . A. Cohort B. Case control C. Cross sectional D. Factorial

C. Cross sectional + Cross - sectional - snapshot in time ? data is collected at a point in time to look at the relationship b / w risk factors and health outcomes in sample populations Ex : random telephone sample to determine if male smokers are more likely to have URI compared to non - smokers .

The ANCOVA Assumptions include all the following EXCEPT : A. The groups DO NOT differ on the covariate B. The covariate is significantly related / correlated to the dependent variable C. The groups DO differ on the covariate D. The correlation about equal for all groups

C. The groups DO differ on the covariate all the other true teachable question

1. A student returning from summer vacation contracts the H1N1 virus . Three months later , in the class of 20 students , 15 students have contracted H1N1 . The attack rate for this infection per month is : A 5 per 100 B 15 per 100 C 20 per 100 D 25 per 100

D 25 per 100 15 in three months is on average 5 per month . The attack rate per 100 is therefore

Items 5 and 6 refer to the table below . Exposed ( many sexual partners ) : HIV ( Cases ) : 40 and No HIV ( Controls ) : 60 Non - exposed ( single faithful sex partner ) : HIV ( Cases ) : 10 and No HIV ( Controls ) : 90 5. The Odds ratio is : A 0.17 B 1 C 2.7 D 6

D 6 Note also that it is calculated using the product of the leading diagonal divided by the product of the aft diagonal

Items 5 and 6 refer to the table below . Exposed ( many sexual partners ) : HIV ( Cases ) : 40 and No HIV ( Controls ) : 60 Non - exposed ( single faithful sex partner ) : HIV ( Cases ) : 10 and No HIV ( Controls ) : 90 6. The data in the table show that: A the risk factor is not related to the disease B the risk factor protects against the disease C among the people studied , a person with HIV is 2.7 times more likely to have been exposed to the risk factor than a person without HIV D among the people studied , a person with HIV is 6 times more likely to have been exposed to the risk factor than a person without HIV

D among the people studied , a person with HIV was 6 times more likely to have been exposed to the risk factor than a person without HIV If the odds ratio is 1 , then the risk factor is not related to the disease ; if it is less than 1 then the risk factor protects against the disease . The value of the odds ratio tells us how many times a person who has the disease was more likely to have been exposed to the risk factor than a person without the disease

13. If the specificity of a test is increased , then which of the following does not occur ? A decreased sensitivity B higher false negatives C lower false positives D higher false positives

D higher false positives What is of the essence here is the definition of specificity .

14. If a treatment has no known side effects , is relatively inexpensive , may significantly reduce morbidity , one should : A set the level of significance of the test at about B reduce the probability of making a type 1 error C increase the probability of making a type 2 error D not be overly concerned about false positives

D not be overly concerned about false positives You would want as many at risk persons as possible to benefit from the treatment . The first three options reduce either the sensitivity or the power of the test .

A study wants to determine the relationship between level of education and test score . Number of hours studied , and amount of practice questions are also assessed . What kind of study is this describing ? A. ANOVA B. Repeated Measures ANOVA C. Factorial ANOVA D. ANCOVA

D. ANCOVA Summary of types of ANOVAs + ANOVA • Helps determine if there is a statistically significant difference b / w the means of 3+ intendent variables ( groups ) Analysis of Covariance ( ANCOVA ) • Assesses whether the means of a dependent variable are equal across levels of an independent variable while controlling for other continuous variables ( covariates ) + Factorial ANOVA • The purpose of this test is to investigate the combined impact of 1+ ( usually 2 3 ) independent variables against 1 dependent variable . + Repeated Measures ANOVA Multiple measures ( repeats ) of the same variable are taken throughout the study .

In this type of study , we are concerned about determining differences in the groups after the treatment . A. Randomized pre - post B. Cohort C. Case control D. Randomized post E. Cross sectional

E. Cross sectional Randomized Post Study + One group gets the treatment , and the other group is the control + You only conduct a post - test . Under the assumption that both groups are equivalent at baseline + In this type of study , we are concerned about determining differences in the groups AFTER the treatment