Epidemiology MIDTERM 2

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how do you calculate incidence in the exposed

# of new cases ---------------------- size of population at start of period

how do you calculate attributable risk?

(incidence in exposed group) - (incidence in nonexposed group)

population attributable risk

(incidence in the unexposed)- (incidence in total population )

how to calculate attributable risk %

(relative risk - 1) / relative risk.

what is internal validity

- DID THE STUDY DO WHAT IT INTENDED TO DO? refers to the design, methods,analysis and the results of an individual study

Concordant pairs

- pairs in which both the case and the control were exposed -pairs in which neither the case nor the control was exposed

what is external validity

-DOES THE STUDY RESULTS APPLY IN THE REAL WORLD? refers to whether rindings that are internally valid are ASLO applicable to people other than those included in an individual study

ethical considerations related to epidemiological studies

-Privacy and confidentiality -Minimizing risks and providing benefits -Avoiding and disclosing conflicts of interest -Informed consent

Discordant pairs

-pairs in which the case was exposed but the control was not - pairs in which the control was exposed but the case was not

what are the different types of bias

-selection bias -information biar -misclassification bias -observer bias -subjective bias -recall bias -surveillance bias

Of 2,872 persons who had received radiation treatment in childhood because of an enlarged thymus, cancer of the thyroid developed in 24 and a benign thyroid tumor developed in 52. A comparison group consisted of 5,055 children who had received no such treatment (brothers and sisters of the children who had received radiation treatment). During the follow-up period, none of the comparison group developed thyroid cancer, but benign thyroid tumors developed in 6. Calculate the relative risk for benign thyroid tumors:

15.3

Smoking question: What are the odds that the controls smoke 1+ pack/day?

1:7 (0.143)

The incidence of CHD in smokers that can be attributed to smoking is:

27.5/1,000

The incidence of lung cancer attributable to smoking in the total population is:

3.6/1,000

Smoking question: Calculate the matched-pairs odds ratio for these data.

4.5

Smoking question: Using data from the table, unmatch the pairs and calculate an unmatched odds ratio.

6.3

The proportion of the risk in the total population that is attributable to smoking is:

78.3%

The proportion of the total incidence of CHD in smokers that is attributable to smoking is:

84.6%

Confidence Intervals

A confidence interval is a range around a point estimate within which the true value is likely to lie with a specified degree of probability, assuming there is no systematic error (bias or confounding). If the sample size is small and subject to more random error, then the estimate will not be as precise, and the confidence interval would be wide, indicating a greater amount of random error. In contrast, with a large sample size, the width of the confidence interval is narrower, indicating less random error and greater precision.

what is the odds ratio( relative odds)

An odds ratio (OR) is a measure of association between a certain property A and a second property B in a population. Specifically, it tells you how the presence or absence of property A has an effect on the presence or absence of property B.

what type of study can relative risk be calculated from?

Cohort study

Different types of causal relationships

Direct-a factor directly causes a disease without any intermediate step(s) Indirect- a factor causes a disease, but only through an intermediate step or steps

How do you calculate risk ratio(CRI)?

Disease risk in exposed _____________________________________ Disease risk in nonexposed

misclassification bias

Misclassification refers to the classification of an individual, a value or an attribute into a category other than that to which it should be assigned

how do you calculate the odds ratio

OR = (a/c)/(b/d) = (ad)/(bc)

how to calculate population attributable risk % (PAR)

PAR / risk(incidence) in population When data on disease incidence is not available we can use the RR... Calculation of PAR% = prevalence in exposed population x (RR-1) / [1+ prevalence in exposed population (RR-1)] ***However, it assumes that all the association between disease and exposure is causal... and PAR varies according to how common an exposure to the risk factor is in the population

difference between probability and odds

Probability is defined as the fraction of desired outcomes in the context of every possible outcome with a value between 0 and 1, where 0 would be an impossible event and 1 would represent an inevitable event. Probabilities are usually given as percentages. Odds can have any value from zero to infinity and they represent a ratio of desired outcomes versus the field. Odds are a ratio, and can be given in two different ways: 'odds in favor' and 'odds against'. 'Odds in favor' are odds describing the if an event will occur, while 'odds against' will describe if an event will not occur.

Difference between systematic error/bias and random error

Random error is also known as variability, random variation, or 'noise in the system'. The heterogeneity in the human population leads to relatively large random variation in clinical trials. Systematic error or bias refers to deviations that are not due to chance alone. The simplest example occurs with a measuring device that is improperly calibrated so that it consistently overestimates (or underestimates) the measurements by X units.

what does it mean when the odds ratio/ risk ratio is equal to 1

Risk in exposed equal to risk in nonexposed no association

what does it mean then the odds ratio/ risk ratio is greater than 1

Risk in exposed greater than risk in nonexposed positive association; possibly causal

what does it mean when odds ratio/risk ratio is less than 1

Risk in exposed less than risk in nonexposed negative association; possibly protective

selection bias

Study population does not represent the target population Repeated attempts to enroll and follow everyone Provide incentives Collect Data on non-respondents Same strategies as for sampling variability

surveillance bias

This happens when there is more intense surveillance/ screening for the outcome among exposed than among unexposed.

when do you know if the odds ratio is a good estimate of relative risk

When the "cases" studied are representative of all people with the disease in the population from which the cases were drawn, with regards to history of the exposure When the "controls" studied are representative of all people without the disease in the population from which the cases were drawn, with regards to history of exposure When the disease being studied is not a frequent one

A prospective cohort study is the preferred study design when: a.) It is unethical to randomize participants into exposed and unexposed groups. b.) Associations between exposure and outcome is necessary. c.) There is not a lot of money and resources to spend. d.) Timely findings are needed.

A retrospective cohort study: a.) Is a study design where exposure is measured from past records and outcome is measured at the time the study is begun. b.) Is a cohort study where exposure and nonexposure are measured as they occur during the study. c.) Is a lot more expensive and time consuming in comparison to a prospective cohort study. d.) Is a synonym of a case-control study

An investigator examined cases of fetal death in 27,000 pregnancies and classified mothers according to whether they had experienced sexual intercourse within 1 month before delivery. It was found that 11% of the mothers of fetuses that died and 2.5% of the mothers of fetuses that survived had had sexual intercourse during the period. It was concluded that intercourse during the month preceding delivery caused the fetal deaths. This conclusion: a. May be incorrect because mothers who had intercourse during the month before childbirth may differ in other important characteristics from those who did not b. May be incorrect because there is no comparison group c. May be incorrect because prevalence rates are used where incidence rates are needed d. May be incorrect because of failure to achieve a high level of statistical significance e. Both b and c

Benefits and risks must be distributed fairly a.) Justice b.) Respect for a persons c.) Beneficence

Collect data on non-respondents a.) Selection bias b.) Information bias

In an outbreak of tuberculosis among prison inmates in Las Vegas, NV 98 of 342 inmates residing on the East wing of the dormitory developed tuberculosis, compared with 17of 385 inmates residing on the West wing. Draw a 2x2 table and answer the following question. What is the risk of tuberculosis for inmates residing in the West wing? a.) 0.04 b.) 0.84 c.) 0.29 d.) 0.92

In epidemiological study design, external validity is not possible without internal validity. a.) True b.) False

Provide participation incentives a.) Selection bias b.) Information bias

Repeat attempts to enroll and follow all participants a.) Selection bias b.) Information bias

The ethical misconduct in the Tuskegee study involved: I- Withholding treatment with penicillin for syphilis II- No informed consent III- Targeting only women IV- Experimental human infection with syphilis a.) I, II and IV b.) I and IV c.) I, II d.) I only

What was the goal of the Willow brook study? a.) to examine the effect of gamma globulin on hepatitis in mentally disabled children b.) to examine the effects of various treatment on mentally disabled children c.) did not have anything to do with on mentally disabled children d.) to test the effect of penicillin to treat syphilis in mentally disabled children

When comparing Cohort studies with Randomized Trials: Both studies compare groups that are exposed and unexposed. The difference between these two designs is the absence or presence of randomization. a.) True b.) False

recall bias

a systematic error caused by differences in the accuracy or completeness of the recollections retrieved ("recalled") by study participants regarding events or experiences from the past.

A recent study identified that the RR=0.80 for getting infected with the flu for those who washed their hands at least 5 times a day. How would you interpret RR=0.80? (assuming statistical significance) a.) Those who washed their hands at least 5 times a day had an increased risk for flu infection. b.) Those who washed their hands at least 5 times a day had a decreased risk for flu infection. c.) Washing hands at least 5 times a day is not protective from being infected with the flu. d.) Results cannot be determined.

A recent study identified that the RR=0.80 for getting infected with the flu for those who washed their hands at least 5 times a day. Which of the following do you think is the most reasonable comparison group? a.) All those who contracted the flu. b.) Those who did not wash their hands at least 5 times a day. c.) Is not necessary because we are estimating absolute risk. d.) Cannot be determined

An Epidemiologist is interested in studying the effectiveness of the varicella (chickenpox) vaccine. He decided to follow 650 children for 5 years starting in 2002 and ending 2007. His findings show that varicella was diagnosed in 42 out of 345 vaccinated children compared with 92 out of 305 unvaccinated children. What is the odds ratio for developing varicella in the vaccinated children compared to unvaccinated children? a.) 0.122 b.) 0.321 c.) 0.403 d.) 0.302

Autonomy of individuals a.) Justice b.) Respect for a persons c.) Beneficence

Blind participants and observers a.) Selection bias b.) Information bias

Calibrate instruments a.) Selection bias b.) Information bias

Factor A, B, or C can each individually cause a certain disease without the other two factors, but only when followed by exposure to factor X. Exposure to factor X alone is not followed by the disease, but the disease never occurs in the absence of exposure to factor X. Factor X is: a. A necessary and sufficient cause b. A necessary, but not sufficient, cause c. A sufficient, but not necessary, cause d. Neither necessary nor sufficient e. None of the above

In 1990, a case-control study was conducted to investigate the positive association between artificial sweetener use and bladder cancer. Controls were selected from a hospital sample of patients diagnosed with obesity-related conditions. Obesity-related conditions have been positively associated with artificial sweetener use. How would the use of these patients as controls affect the estimate of the association between artificial sweetener use and bladder cancer? a. The estimate of association would accurately reflect the true association regardless of the association between artificial sweetener use and obesity-related conditions b. The estimate of association would tend to underestimate the true association c. More information is needed on the strength of association between artificial sweetener use and obesity-related conditions before any judgment can be made d. The estimate of association would tend to overestimate the true association e. More information is needed on the strength of association between artificial sweetener use and bladder cancer before any judgment can be made

In an outbreak of tuberculosis among prison inmates in Las Vegas, NV 98 of 342 inmates residing on the East wing of the dormitory developed tuberculosis, compared with 17of 385 inmates residing on the West wing. Draw a 2x2 table and answer the following question. What is the risk ratio (cumulative incidence ratio) of developing TB for inmates residing in the East wing (exposed) of the dormitory compared to the West wing (unexposed)? a.) 3.8 b.) 6.5 c.) 5.6 d.) 8.6

It has been suggested that physicians may examine women who use oral contraceptives more often or more thoroughly than women who do not. If so, and if an association is observed between phlebitis and oral contraceptive use, the association may be due to: a.) Nonresponse bias b.) Surveillance bias c.) Interview bias d.) Selection bias

Persons with diminished autonomy are entitled to protection a.) Justice b.) Respect for a persons c.) Beneficence

Several studies have found that approximately 85% of cases of lung cancer are due to cigarette smoking. This measure is an example of: a.) Cumulative Incidence b.) An attributable risk c.) A prevalence risk d.) A proportionate mortality ratio

Several studies have found that approximately 85% of cases of lung cancer are due to cigarette smoking. This measure is an example of: a. An incidence rate b. An attributable risk c. A relative risk d. A prevalence risk e. A proportionate mortality ratio

Statistical testing will account for differential misclassification. a.) True b.) False

The cohort study is an example of a: a.) Randomized trial b.) Observational Study c.) Descriptive Study d.) Experimental

Use unobtrusive measures a.) Selection bias b.) Information bias

An Epidemiologist is interested in studying the effectiveness of the varicella (chickenpox) vaccine. He decided to follow 650 children for 5 years starting in 2002 and ending 2007. His findings show that varicella was diagnosed in 42 out of 345 vaccinated children compared with 92 out of 305 unvaccinated children. What is the risk for developing varicella in the vaccinated children? a.) 0.37 b.) 0.403 c.) 0.122 d.)0.302

In a cohort study that investigated the association between eating daily intake of cruciferous vegetables and cancer, the following was observed: -50 ate cruciferous vegetables daily and was diagnosed with cancer at the end of follow-up -100 did not eat cruciferous vegetables and was diagnosed with cancer at the end of follow-up -50 ate cruciferous vegetables daily and was not diagnosed with cancer at the end of follow-up -50 did not eat cruciferous vegetables and was not diagnosed with cancer at the end of follow-up. When comparing the RR and OR of the relationship between daily consumption of cruciferous vegetables and cancer, which statement best explains your observation a.) OR is an appropriate approximation of RR because they are measuring associations the same way. b.) Cannot really compare because we need to repeat the study using the case-control study design. c.) OR is not an appropriate approximation of RR because the outcome is not rare. d.) OR is not an appropriate approximation of RR because the exposure of interest is not rare

In a large case-control study of patients with pancreatic cancer, 17% of the patients were found to be diabetic at the time of diagnosis, compared to 4% of a well-matched control group (matched by age, sex, ethnic group, and several other characteristics) that was examined for diabetes at the same time as the cases were diagnosed. It was concluded that the diabetes played a causal role in the pancreatic cancer. This conclusion: a. Is correct b. May be incorrect because there is no control or comparison group c. May be incorrect because of failure to establish the time sequence between onset of the diabetes and diagnosis of pancreatic cancer d. May be incorrect because of less complete ascertainment of diabetes in the pancreatic cancer cases e. May be incorrect because of more complete ascertainment of pancreatic cancer in nondiabetic persons

In an outbreak of tuberculosis among prison inmates in Las Vegas, NV 98 of 342 inmates residing on the East wing of the dormitory developed tuberculosis, compared with 17of 385 inmates residing on the West wing. Draw a 2x2 table and answer the following question. What is the odds ratio of developing TB for inmates residing in the East wing of the dormitory compared to the West wing? a.) 6.5 b.) 0.11 c.) 8.7 d.) 3.8

It has been suggested that physicians may examine women who use oral contraceptives more often or more thoroughly than women who do not. If so, and if an association is observed between phlebitis and oral contraceptive use, the association may be due to: a. Selection bias b. Interviewer bias c. Surveillance bias d. Nonresponse bias

Malignant mesothelioma is a rare cancer that develops from the cells of the mesothelium, the protective lining that covers many of the internal organs of the body. The latency period is 35 to 40 years between exposure and diagnosis. Which study design would you recommend to investigate the predictors of this illness? a.) Cross-sectional b.) Prospective cohort study c.) Retrospective cohort study d.) Experimental study design

Respect persons' decisions and protect from harm a.) Justice b.) Respect for a persons c.) Beneficence

What are the threats to validity in epidemiological study data? a.) Prospective cohort study b.) Infectious diseases c.) Random error, bias, and confounding d.) There are no threats, the data is always true

What is the correct interpretation of the odds ratio? a.) Children who received a vaccine were X% less likely to develop varicella than those children who did not receive the vaccine. b.) Children who received a vaccine had X less odds of developing varicella than those children who did not receive the vaccine. c.) Children who received a vaccine had X times the odds of developing varicella when compared to those children who did not receive the vaccine. d.) Children who received a vaccine were X% more likely to develop varicella than those children who did not receive the vaccine.

maximize possible benefits a.) Justice b.) Respect for a persons c.) Beneficence

minimize possible harms a.) Justice b.) Respect for a persons c.) Beneficence

An Epidemiologist is interested in studying the effectiveness of the varicella (chickenpox) vaccine. He decided to follow 650 children for 5 years starting in 2002 and ending 2007. His findings show that varicella was diagnosed in 42 out of 345 vaccinated children compared with 92 out of 305 unvaccinated children. What is the risk for developing varicella in the unvaccinated children? a.) 0.370 b.) 0.122 c.) 0.403 d.) 0.302

An Epidemiologist is interested in studying the effectiveness of the varicella (chickenpox) vaccine. He decided to follow 650 children for 5 years starting in 2002 and ending 2007. His findings show that varicella was diagnosed in 42 out of 345 vaccinated children compared with 92 out of 305 unvaccinated children. What is the risk ratio (cumulative incidence ratio) for developing varicella in the vaccinated children compared to unvaccinated children? a.) 0.122 b.) 0.302 c.) 0.370 d.) 0.404

Factor A, B, or C can each individually cause a certain disease without the other two factors, but only when followed by exposure to factor X. Exposure to factor X alone is not followed by the disease, but the disease never occurs in the absence of exposure to factor X. Factor A is: a. A necessary and sufficient cause b. A necessary, but not sufficient, cause c. A sufficient, but not necessary, cause d. Neither necessary nor sufficient e. None of the above

In a cohort study that investigated the association between eating daily intake of cruciferous vegetables and cancer, the following was observed: -50 ate cruciferous vegetables daily and was diagnosed with cancer at the end of follow-up -100 did not eat cruciferous vegetables and was diagnosed with cancer at the end of follow-up -50 ate cruciferous vegetables daily and was not diagnosed with cancer at the end of follow-up -50 did not eat cruciferous vegetables and was not diagnosed with cancer at the end of follow-up Assuming this relationship is causal, what does RR and OR tell us about the relationship between daily consumption of cruciferous vegetables and cancer? a.) Daily consumption of cruciferous vegetables is positively associated with being diagnosed with cancer b.) Daily consumption of cruciferous vegetables is not associated with cancer c.) Cannot determine because RR and OR provide different information regarding the relationship between an exposure and an outcome. d.) Daily consumption of cruciferous vegetables reduces the risk of cancer

Loss to follow-up or attrition is: a.) A problem because participants stop participating in the cohort study during follow-up b.) A problem that can lead to selection bias. c.) A problem because the incidence rates among those exposed and those unexposed might be difficult to interpret. d.) All listed answers.

What is the correct interpretation for the risk ratio (cumulative incidence ratio)? a.) Children who received a vaccine were X% less likely to develop varicella than those children who did not receive the vaccine. b.) Children who received a vaccine were X% more likely to develop varicella than those children who did not receive the vaccine. c.) Children who received a vaccine had X less risk of developing varicella than those children who did not receive the vaccine. d.) Children who received a vaccine had X times the risk of developing varicella when compared to those children who did not receive the vaccine.

When comparing the relative risk and attributable risk, which is true: a.) All of the listed answers. b.) Both relative risk and attributable risk are important measures of the strength of association. c.) Neither is useful in major applications in clinical practice and public health. d.) Relative risk is valuable in etiologic studies of disease, whereas attributable risk has major applications in clinical practice and public health.

Which estimate and confidence interval is not very precise but is significant? a.) OR=1.60 (95% CI=0.80, 2.60) b.) OR=1.01 (95% CI=0.95,1.07 c.) OR=1.60 (95% CI=1.50,1.70) d.) OR=1.60 (95% CI=1.04, 2.60)

Which estimate and confidence interval is very precise but insignificant? a.) OR=0.90 (95% CI=0.65,0.95) b.) OR=0.65 (95% CI=0.20,0.98) c.) OR=0.90 (95% CI=0.85,0.95) d.) OR=0.90 (95%CI=0.85,1.05)

Which is true of absolute risk? a.) All of the listed answers. b.) It can indicate whether the exposure is associated with an increased risk for disease. c.) It is the same as relative risk. d.) It can indicate the magnitude of the risk in a group of people with a certain exposure.

Which is true regarding case-control studies and relative risk? a.) Relative risk is not possible as long as you can determine the number of new cases b.) Relative risk is not possible because case-control studies occur at one point in time c.) Relative risk is not possible as long as there is a comparison group d.) Relative risk is not possible because incidence rates are not measured in case-control studies.

All of the following are important criteria when making causal inferences except: a. Consistency with existing knowledge b. Dose-response relationship c. Consistency of association in several studies d. Strength of association e. Predictive value

In a study of a disease in which all cases that developed were ascertained, if the relative risk for the association between a factor and the disease is equal to or less than 1.0 , then: a. There is no association between the factor and the disease b. The factor protects against development of the disease c. Either matching or randomization has been unsuccessful d. The comparison group used was unsuitable, and a valid comparison is not possible e. There is either no association or a negative association between the factor and the disease

Which of the following is an approach to handling confounding? a. Individual matching b. Stratification c. Group matching d. Adjustment e. All of the above

information bias

happens during data collection and may be several types: Hundres! Recall bias Surrogate bias Interviewer bias Use unobtrusive measures Blind participant, observer calibrate instruments same strategies for measurement error

Precision

how close estimates from different samples are to each other.

Accuracy

if it is close to the truth with repeated measurement (or repeated surveys).

observer bias

occurs when there are systematic differences in the way information is collected for the groups being studied. Observer bias may occur as a result of the investigator's prior knowledge of the hypothesis under investigation or knowledge of an individual's exposure or disease status.

What is risk Ratio(CRI)?

probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group.

When is risk ratio used(CRI)?

relative risk or risk ratio (RR) is the ratio of the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group. Relative risk includes two important features: (i) a comparison of risk between two "exposures" puts risks in context, and (ii) "exposure" is ensured by having proper denominators for each group representing the exposure

subjective bias

sometimes called personal validation effect, is a cognitive bias by which a person will consider a statement or another piece of information to be correct if it has any personal meaning or significance to them.

Belmont report

summarizes ethical principles and guidelines for research involving human subjects. Three core principles are identified: respect for persons, beneficence, and justice.

what is attributable risk?

the difference in rate of a condition between an exposed population and an unexposed population. Attributable risk is mostly calculated in cohort studies, where individuals are assembled on exposure status and followed over a period of time.

Matching

the process of selecting controls so that they are similar to the cases in certain characteristics, such as age, race, sex, socioeconomic status, and occupation There are 2 types: Group Individual

Type 1 error

there is no difference between therapies false postive Rejecting the null hypothesis when it is true

Type 2 error

this is a difference between therapies false negative Accepting the null hypothesis when it is false

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