Epidemiology Review

incidence rates may be computed directly

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

type I error (alpha error)

A randomized trial comparing the efficacy of two drugs showed a difference between the two (with a P-value <.05). Assume that in reality, however, the two drugs do not differ. This is therefore an example of: A. Type I error (α error) B. Type II error (β error) C. 1 - α D. 1 - β E. None of the above

May be incorrect because no test of statistical significance was used

An advertisement in a medical journal stated that "2,000 subjects with sore throats were treated with our new medicine. Within 4 days, 94% were asymptomatic." The advertisement claims that the medicine was effective. Based on the evidence given above, the claim: A. Is correct B. May be incorrect because the conclusion is not based on a rate C. May be incorrect because of failure to recognize a long-term cohort phenomenon D. May be incorrect because no test of statistical significance was used E. May be incorrect because no control or comparison group was involved

False

Case-Control Studies are prospective in that they follow the cases and controls over time and observe what occurs a) True b) False

identifying risk factors associated with a disease

Cohort Studies generally look at which of the following? a) Determining the sensitivity and specificity of diagnostic methods b) Identifying risk factors associated with a disease c) Variations among the clinical manifestations of patients with a disease d) The impact of blinding or masking a study population e) a, c, and d

cohort study

Following a large group of cigarette smokers for a period of 10 years to determine the occurrence of chronic obstructive pulmonary disease, coronary heart disease, and various forms of lung cancer would be an example of a A. randomized clinical trial B. cross-sectional study C. prevalence study D. cohort study E. case-control study

True

In a cohort study, an exposure is assessed and then participants are followed prospectively to observe whether they develop the outcome a) True b) False

a number of exposures can be studied simultaneously

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

there is a difference between children with a history of paroxysmal nocturnal hemoglobinuria and normal children with respect to the incidence of complement-sensitive associated anemia 95% of the time

In a longitudinal study of the relationship between paroxysmal nocturnal hemoglobinuria and the subsequent onset of complement-sensitive associated anemia, 150 children were followed for a period of three years. At a significance level of P-value < 0.05, the alternate hypothesis states that A. there is an insignificant difference between children with a history of paroxysmal nocturnal hemoglobinuria and normal children with respect to the incidence of complement-sensitive associated anemia B. there is no difference between children with a history of paroxysmal nocturnal hemoglobinuria and normal children with respect to the incidence of complement-sensitive associated anemia C. there is a difference between children with a history of paroxysmal nocturnal hemoglobinuria and normal children with respect to the incidence of complement-sensitive associated anemia 5% of the time D. there is a difference between children with a history of paroxysmal nocturnal hemoglobinuria and normal children with respect to the incidence of complement-sensitive associated anemia 95% of the time E. there is no difference between children with a history of paroxysmal nocturnal hemoglobinuria and normal children with respect to the incidence of complement-sensitive associated anemia 95% of the time

the null hypothesis may be rejected even though the results could have occurred purely by chance a maximum of 5% of the time

In a prospective study, the occurrence of transitional cell carcinoma of the bladder was recorded for smokers and nonsmokers. The difference in incidence between smokers and nonsmokers was reported to be significant at the P-value < 0.05 level. The most appropriate statement that can be made about this study is that A. the null hypothesis may be rejected even though the results could have occurred purely by chance a maximum of 5% of the time B. a significant difference in the incidence between smokers and nonsmokers may occur 5% of the time or less C. the null hypothesis may be accepted because there is a difference in the incidence rates between smokers and nonsmokers only 5% of the time D. the alternate hypothesis may be rejected because the null hypothesis is true up to 5% of the time E. a causal relationship between smoking and the incidence of transitional-cell carcinoma of the bladder may be established at a significance level of 0.05

both b and c

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 non-exposed groups under study be as similar as possible with regard to possible confounding factors E. Both b and c

The pattern of association could be expressed by a straight-line function

In many studies examining the association between estrogens and endometrial cancer of the uterus, 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

T, T, F, F

Please label the following statements as true (T) or false (F) regarding bias in epidemiologic research. ( ) Bias is an error in design or execution of a study that produces results that are consistently distorted in one direction and lead to an incorrect assessment of the association between the factor and the disease under study ( ) Bias could be due to problems in the selection of the population to be studied ( ) Bias can be prevented or minimized by taking a larger sample ( ) Bias can occur in observational studies

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

Retrospective cohort studies are characterized by all of the following except: A. The study groups are exposed and non-exposed 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

provide assurance of the significance of the findings

Statistical methods are used in medical research because they A. provide values for results that are dependent upon chance B. provide conclusions about cause and effect C. provide controls for variables that were absent in the study design D. provide assurance of the significance of the findings E. provide controls for some of the more common sources of experimental error

True

T or F: Case-reports are not considered evidence-based even though the authors have studied the case in great depth.

Reduce selection bias in the allocation of treatment

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 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

a retrospective cohort study

The physical examination records of the entire incoming freshman class of 1945 at the University of North Dakota were examined in 1987 to see if their recorded height and weight at the time of admission to the university was related to the development of coronary heart disease by 1996. This is an example of: A. A cross-sectional study B. A case-control study C. A concurrent cohort study D. A retrospective cohort study E. An experimental study

Avoid observer and subject bias

The purpose of a double-blind or double masked study is to: A. Achieve comparability of treated and untreated subjects B. Reduce the effects of sampling variation. C. Avoid observer and subject bias D. Avoid observer bias and sampling variation E. Avoid subject bias and sampling variation

ecological study

To investigate whether there is an association between smoking and type 2 diabetes, a researcher asked a group of people if they are currently smoking and if they had type 2 diabetes. In answering "yes" to smoking, the individual was asked how many packs/day. What kind of study design is this? A. Cohort study B. Ecological study C. Randomized control study D. Cross-sectional study E. Case-report

B

What is the purpose of the control group in a case-control study? a) To provide information on the disease distribution in the population that gave rise to the cases b) To provide information on the exposure distribution in the population that gave rise to the cases c) a and b

when new symptoms are outcomes are unidentified

When are Case-reports most useful? a) When you encounter common cases and need more information b) When new symptoms or outcomes are unidentified c) When developing practice guidelines d) When the population being studied is very large e) All of the above

obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study

Which of the following is a case-control study? A. Study of past mortality or morbidity trends to permit estimates of the occurrence of disease in the future B. Analysis of previous research in different places and under different circumstances to permit the establishment of hypotheses based on cumulative knowledge of all known factors C. Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study D. Study of the incidence of cancer in men who have quit smoking E. Both a and c

a, b, and c

Which of the following is an advantage of Case-Control Studies? a) They can simultaneously look at multiple risk factors b) They are useful to initially establish an association between a risk factor and a disease c) They take less time to complete because the condition or disease has already occurred d) b and c only e) a, b, and c

stratification, randomization, matching, adjustment using multi-variable analysis

ways to control for effects of confounding