Epi Review Questions

The ratio between food-specific attack rates of those who ate a certain food compared to those who did not eat it is: A. An odds ratio B. A prevalence ratio C. A relative risk D. An attributable risk E. None of the above

C. A relative risk

Which of the following is a true conclusion concerning matching? A. Once we have matched controls to cases according to a given characteristic, we can only study that characteristic when the prevalence of disease is low B. If an attempt is made to match according to too many characteristics, it may prove difficult or impossible to adjust for the all of the characteristics during data analysis C. Matching on many variables may make it difficult to find an appropriate control D. Individual matching differs from frequency matching because controls are selected from hospitals instead of from the general population E. None of the above

C. Matching on many variables may make it difficult to find an appropriate control

Residents of villages with different water supplies were asked to participate in a survey to ID cholera carriers. Because several cholera deaths had occurred, virtually everyone present at the time underwent examination. The proportion of residents in each village who were carriers was computed and compared. What is the proper classification for this study? a. cross-sectional b. case control c. prospective cohort d. retrospective cohort e. experimental

a. cross-sectional

In a certain community, the average 5-year survival from colon cancer is 12%. After a screening program is introduced, the average 5-year survival is 23%. The most likely explanation for this difference is: a. interviewer bias b. non-response bias c. recall bias d. lead-time bias e. information bias

d. lead-time bias

A major problem in using a historical control design for evaluating a health service using case fatality as an outcome is that if the CF is lower after provision of the health service was started then, a. the lower CF could be caused by changing prevalence of the disease b. the lower CF may be a result of decreasing incidence c. the lower CF may be an indirect effect of the new health service d. the CF may have been affected by changes in factors that are not related to the new health service e. none fo the above

d. the CF may have been affected by changes in factors that are not related to the new health service

In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that: a. there be equal numbers of persons in both study groups b. at the beginning of the study, those with the disease and those without the disease have equal risks of having the factor c. the study group with the factor and the study group without the factor be representative of the general population d. the exposed and nonexposed groups under study be as similar as possible with regard to possible confounding factors e. both b and c

d. the exposed and nonexposed groups under study be as similar as possible with regard to possible confounding factors

To be causally related to a disease, an etiologic factor must satisfy certain conditions. Which of the following is NOT one of the conditions? a. the factor is found more frequently among the diseased than the non-diseased b. exposure to the factor precedes the development of the disease c. elimination of the factor can reduce the risk of the disease d. the factor is found among all cases with the disease e. those with the factor have a higher incidence of disease than those without the factor

d. the factor is found among all cases with the disease

In a randomized clinical trial comparing a standard and an experimental treatment, alpha (α), or Type I error, equals 0.2. Which of the following is true? A. The probability of concluding that the treatments differ, when in reality they do not differ, is 20% B. The probability of concluding that the treatments differ, when in reality they do not differ, is 80% C. The probability of concluding that the treatments do not differ, when in reality they do not differ, is 20% D. The probability of concluding that the treatments differ, when in reality they do differ, is 20% E. The probability of concluding that the treatments do not differ, when in reality they do differ, is 80%

A. The probability of concluding that the treatments differ, when in reality they do not differ, is 20%

Anyone who is born with trisomy 21 (a condition with an extra chromosome) will have mental retardation. However, some people will have mental retardation for other reasons. In this example trisomy 21 is a: A. Necessary cause B. Sufficient cause C. Neither necessary nor sufficient cause D. Necessary and sufficient cause E. Confounding factor

B. Sufficient cause

In 1976, a randomized clinical trial was carried out which compared total mastectomy and segmental (partial) mastectomy in the treatment of breast cancer. A total mastectomy was carried out on any woman assigned to the segmental mastectomy group if it was impossible to obtain tumor-free margins (i.e., it seemed that the tumor had spread). For statistical analysis, these women were retained in the segmental group. Was this procedure reasonable? A. No, these women were treated with total mastectomy and should have been placed in the total mastectomy group for statistical analysis B. Yes, excluding these women from statistical analysis would have biased the outcome in favor of the segmental mastectomy group. C. No, these women did not undergo the segmental mastectomy procedure and should have been dropped from the statistical analysis D. Yes, including these women in the total mastectomy group would have biased the outcome against the segmental mastectomy group E. No, these women were clearly not representative of women who were originally assigned to the segmental mastectomy group so they should have been dropped from the statistical analysis

B. Yes, excluding these women from statistical analysis would have biased the outcome in favor of the segmental mastectomy group.

The main purpose of randomization in a vaccine study is to: A. minimize placebo reactions B. avoid bias in the assignment of treatment C. make the efficacy of the vaccine equal in the two groups D. minimize vaccine reactions E. ensure that the rates of influenza observed in the two groups will be the same

B. avoid bias in the assignment of treatment

A researcher wants to assess alcohol consumption as a risk factor for head and neck cancer. She uses a nested case-control study in a cohort of adult females to answer this question. Which two groups are best to select and compare for this purpose? A. All alcohol drinkers in the cohort and a group who did not drink alcohol individually matched to the alcohol drinkers on case status. B. All alcohol drinkers in the cohort and a group who did not drink alcohol individually matched to the alcohol drinkers for age. C. All head and neck cancer cases in the cohort and a group who did not develop head and neck cancer individually matched to the cases for age. D. All head and neck cancer cases in the cohort and a group who did not develop head and neck cancer individually matched to the cases for alcohol consumption. E. A subset of the alcohol drinkers in the cohort and a group who did not drink alcohol individually matched to the drinkers for age.

C. All head and neck cancer cases in the cohort and a group who did not develop head and neck cancer individually matched to the cases for age.

An important assumption involved in the use of person-weeks in a study that follows subjects over time is that: A. the subjects have been randomly selected from a defined population B. a placebo group has been used C. the risk of disease is constant over the period of observation for each group studied D. the disease is rare E. the risk of disease is similar in treatment and control groups

C. the risk of disease is constant over the period of observation for each group studied

Which of the following statements regarding type I and/or type II error is TRUE? A. A type I error is the probability of concluding the treatments do not differ when in reality they do differ. B. Power is defined as the probability of making a type II error. C. α is the probability of detecting a difference between treatments if the treatments do actually differ. D. 1-β is the probability of detecting a difference between the treatments if the treatments do actually differ. E. Both A and D.

D. 1-β is the probability of detecting a difference between the treatments if the treatments do actually differ.

Attributable risk is: A. The risk of a population group possessing a characteristic, as a multiple of the group lacking the characteristic B. The number of cases that are explained by a given factor C. The ratio of the incidence rates in those exposed to a factor compared to those not exposed to the factor D. The difference in the incidence of disease over time comparing those exposed to a factor to those not exposed to that factor E. The ratio incidence rates in those not exposed to a factor compared to those exposed to the factor

D. The difference in the incidence of disease over time comparing those exposed to a factor to those not exposed to that factor

In 2000, investigators began a study to examine a possible association between depression and Parkinson's disease. 1,358 subjects with depression diagnosed between 1975 and 1995 were identified using records from general practices in the Netherlands. A group of 67,570 patients from the same practices with no diagnosis of depression were also included in the study. All subjects were followed until 2000 for diagnosis of Parkinson's disease by reviewing available subject medical records. Of the subjects with diagnosed depression, 19 developed Parkinson's disease. 259 of the subjects without a diagnosis of depression developed Parkinson's disease. 34. What type of study design is this? A. case-control B. cross-sectional C. prospective cohort D. retrospective cohort E. randomized clinical trial

D. retrospective cohort

In a study of 500 cases of a disease and 500 controls, the suspected etiologic factor is found in 400 of the cases and 100 of the controls. The absolute risk (cumulative incidence) of disease in persons with the factor is: A. 80% B. 40% C. 16% D. 20% E. Cannot be computed from the data given

E. Cannot be computed from the data given

Children with a negative history for mumps were randomly allocated to one of two groups. The first group received live attenuated mumps virus vaccine and the other group received a suitably disguised placebo. An outbreak of mumps occurred a few months later. After it had subsided, mumps attack rates were computed for the two groups. Classify the study as to the following: A. cross-sectional study B. case-control study C. prospective cohort study D. retrospective cohort study E. randomized clinical trial

E. randomized clinical trial

A case-control study was conducted to investigate the positive association between artificial sweeteners 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?

The estimate of the association would tend to underestimate the true association.

Which of the following is correct regarding the use of the life table and the Kaplan-Meier approaches for calculating survival? a. The life table method has time intervals determined by study investigators whereas time intervals in the Kaplan-Meier method are determined by the time when each outcome occurs b. In the life table method, persons lost to follow-up are at higher risk of the outcome compared to those who remain in the study c. The life table method calculates probability of survival at the time of the event d. Median survival time can be calculated by the life table method, but not the Kaplan Meier method e. In both methods, we assume that the risk of the outcome occurs at the same rate across the interval

a. The life table method has time intervals determined by study investigators whereas time intervals in the Kaplan-Meier method are determined by the time when each outcome occurs

It has been demonstrated that the crude in-hospital case fatality ratio for MI is higher for females then men. However, females are older when they have MIs. On the basis of these data, one could say that there is an association between gender and in-hospital CFR from MI if comparisons by gender are based on: a. age-specific case fatality ratios b. studies involving only males c. studies involving only females d. community-based mortality rates e. gender differences in the crude case-fatality ratios

a. age-specific case fatality ratios

The extent to which a specific health care treatment, service, etc. produces a beneficial result under ideal controlled conditions is its: a. efficacy b. effectiveness c. effect modification d. efficiency e. none of the above

a. efficacy

Which of the following is NOT an advantage of a prospective cohort study? a. it usually costs less than a case-control study b. precise measurement of exposure is possible c. incidence rates can be calculated d. recall bias is minimized compared with a case-control study e. many disease outcomes can be studied simultaneously

a. it usually costs less than a case-control study A prospective cohort study usually costs MORE than a case control study

A major problem resulting from the lack of randomization in a cohort study is: a. the possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease b. the possibility that a greater proportion of people in the study may have been exposed c. the possibility that a smaller proportion of people in the study may have been exposed d. that, without randomization, the study may take longer to carry out e. planned crossover is more likely

a. the possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease

In a study begun in 1965, a group of 3,000 adults in Baltimore were asked about alcohol consumption. The occurrence of cases of cancer between 1981 and 1995 was studied in this group. This is an example of: a. a cross-sectional study b. a prospective cohort c. a retrospective cohort d. a clinical trial e. a case-control study

b. a prospective cohort

The extent to which a specific health care treatment, service, etc. does what it is intended to do when used in a community-dwelling population is termed its: a. efficacy b. effectiveness c. effect modification d. efficiency e. none of the above

b. effectiveness

In a randomized trial, a planned crossover design: a. eliminates the problem of a possible order effect b. must take into account the problem of possible residual effects of the first therapy c. requires stratified randomization d. eliminates the need for monitoring compliance and noncompliance e. enhances the generalizability of the results of the study

b. must take into account the problem of possible residual effects of the first therapy

All of the following are measures of process of health care in a clinic except: a. proportion of patients in whom blood pressure is measured b. proportion of patients who have complications of disease c. proportion of patients advised to stop smoking d. proportion of patients whose height and weight are measured e. proportion of patients whose bill is reduced because of financial need

b. proportion of patients who have complications of a disease

In many studies examining the association between estrogen and endometrial cancer, a one-sided significance test was used. The underlying assumption justifying a one-sided rather than a two-sided test is: a. the distribution of the proportion exposed followed a "normal" pattern b. the expectation before doing the study was that estrogens cause endometrial cancer of the uterus c. the pattern of association could be expressed by a straight-line function d. type ii error was the most important potential error to avoid e. only one control group was being used

b. the expectation before doing the study was that estrogens cause endometrial cancer of the uterus

If a difference is observed in the occurrence of a disease in a particular pair of monozygotic (identical) twins, the difference is most likely due to: a. exclusively to hereditary factors b. to non-hereditary factors c. to both hereditary and non-hereditary factors d. almost exclusively to hereditary factors with some non-hereditary factors playing a role e. none of the above

b. to non-hereditary factors

In a cohort study, the advantage of starting by selecting a defined population for study before any of its members become exposed, rather than starting by selecting exposed and non-exposed individuals, is that: a. the study can be completed more rapidly b. a number of outcomes can be studied simultaneously c. a number of exposures can be studied simultaneously d. the study will cost less to carry out e. a and d

c. a number of exposures can be studied simultaneously

Ecological fallacy refers to: a. assessing exposure in large groups rather than in many small groups b. assessing outcome in large groups rather than in many small groups c. ascribing the characteristics of a group to every individual in that group d. examining correlations of exposure and outcomes rather than time trends e. failure to examine temporal relationships between exposures and outcomes

c. ascribing the characteristics of a group to every individual in that group

A case control study is characterized by all of the following except: a. it is relatively inexpensive compared with most other epidemiologic study designs b. patients with the disease (cases) are compared with persons without the disease (controls) c. incidence rates may be computed directly d. assessment of past exposure may be biased e. definition of cases may be difficult

c. incidence rates may be computed directly You cannot compute incidence rates or prevalence rates from case control studies.

The best measure(s) of the strength of association is/are: a. prevalence b. attributable risk c. relative risk d. incidence rate e. a, b, and c

c. relative risk

All of the following are potential benefits of a randomized clinical trial, except: a. the likelihood that the study groups will be comparable is increased b. self-selection for a particular treatment is eliminated c. the external validity of the study is increased d. assignment of the next subject cannot be predicted e. the therapy that subject receives is not influenced by either conscious or subconscious bias of the investiator

c. the external validity of the study is increased

Retrospective cohort studies are characterized by all of the following except: a. the study groups are exposed and nonexposed b. incidence rates may be computed c. the required sample size is smaller than that needed for a prospective cohort study d. the required sample size is similar to that needed for a prospective cohort study e. they are useful for rare exposures

c. the required sample size is smaller than that needed for a prospective cohort study

Among the guidelines for judging whether an association is causal, which of the following is the weakest and most controversial guideline? a. Strength of the association b. Dose-response c. Temporal relationship d. Specificity of the association e. Biologic plausability

d. Specificity of the association

Investigators identify people w/disease X and divide them into 2 groups. Those with an advanced stage of disease and those with an early stage of the disease. Each of these groups is studied to ID who had received screening for disease X in the past and who had never been screened for disease X. This is an example of what type of study design of the benefits of screening? a. prospective cohort study b. a randomized clinical trial c. a cross-sectional study d. a case-control study e. none of the above

d. a case-control study

The absolute difference between the food-specific attack rate of those who ate a certain food and those who did not eat it is essentially: a. an incidence rate b. prevalence c. a relative risk d. an attributable risk e. none of the above

d. an attributable risk

In which one of the following types of study designs does a subject serve as his own control? a. prospective cohort study b. retrospective cohort study c. case-cohort study d. case-crossover study e. case-control study

d. case-crossover study

The extent to which the resources used to provide a specific health treatment, service, procedure, program or other intervention are expended is its: a. efficacy b. effectiveness c. effect measure d. efficiency e. none of the above

d. efficiency

The best measure of absolute risk of disease is: a. prevalence b. case-fatality rate c. population attributable risk d. incidence rate e. relative risk

d. incidence rate

The physical exam records of the freshman class of 1935 at UMinnesota were examined in 1977 to see if their recorded height and weight at the time of admission was related to the dev't of CHD by 1986. This is an example of: a. cross-sectional b. case-control c. prospective cohort d. retrospective cohort e. experimental study

d. retrospective cohort

Which of the following is correct about clinical trial designs? a. the purpose of masking in a randomized trial is primarily to prevent potential bias in treatment assignment b. the purpose of randomization in a clinical trial is primarily to remove potential bias in reporting side effects of the investigative drugs c. the effect of investigative drugs on a disease that can be cured cannot be assessed using the factorial design even if the drugs act independently and anticipated outcomes are different d. the washout period in a crossover trial is meant to primarily prevent potential carryover of treatment effects and psychological responses e. the parallel treatment design increases participant enrollment interests because each participant will receive both of the interventions being tested

d. the washout period in a crossover trial is meant to primarily prevent potential carryover of treatment effects and psychological responses

In a case-control study, which of the following is true? a.The proportion of cases with the exposure is compared with the proportion of controls with the exposure b. disease rates are compared for people with the factor of interest and for people without the factor of interest c. the investigator may choose to have multiple comparison groups d. recall bias is a potential problem e. a, c, and d

e. a, c, and d In a case-control study: a.The proportion of cases with the exposure is compared with the proportion of controls with the exposure c. the investigator may choose to have multiple comparison groups d. recall bias is a potential problem

Which of the following is/are criteria for selecting a morbidity index to serve as a measure of effectiveness of a screening program: a. relatively easy to define and diagnose b. available methods of prevention and intervention are known to "work" c. quantifiable d. both the population served and the comparison population must be at risk for the condition e. all of the above

e. all of the above

The major purpose of random assignment in a clinical trial is to: a. help ensure that study subjects are representative of the general population b. facilitate double blinding (masking) c. facilitate the measurement of outcome variables d. ensure that the study groups have comparable baseline characteristics e. reduce selection bias in the allocation of treatment

e. reduce selection bias in the allocation of treatment