Question 1

-Which term most accurately describes the following definition? "Analysis based on aggregated or grouped data; errors in inference may result because associations may be artifactually created or masked by the aggregation process." [Porta M,ed.A Dictionary of Epidemiology.New York: Oxford University Press; 2014.]

Accepted Answer

Ecologic studies are studies of group characteristics to determine whether an association exists."Cross-sectional study" is not correct.Cross-sectional studies define a population and determine the presence or absence of exposure and the presence or absence of disease for each individual at the same time.Both exposure and disease outcome are determined simultaneously for each subject."Case-control study" is not correct.In case-control studies,investigators identify a group of individuals with the disease and a group of individuals without the disease to examine the possible relation of an exposure to a certain disease."Cohort study" is not correct.In cohort studies,investigators select a group of exposed individuals and a group of nonexposed individuals and follows up both groups to compare the incidence of disease in two groups."Randomized trial" is not correct.A randomized trial is a clinical-epidemiologic experiment in which subjects are randomly allocated into groups,usually called test and control groups,to receive or not to receive a preventive or a therapeutic procedure or intervention.

Question 2

Which of the following biases is the most accurate explanation of the following situation? Epidemiologists are studying the possible relationship of cholera infections to drinking water.They conduct a case-control study and interview patients with cholera infection (cases) and persons without cholera infection (controls).A patient who was diagnosed with cholera often tries to identify all kinds of information related to drinking water.However,controls who were not diagnosed with cholera may not remember water they drink which is not from an unhygienic source.

Accepted Answer

In a case-control study,cases are more likely to recall exposures that they believe may have contributed to the outcome."Selection bias," "Misclassification bias," "Exclusion bias" are related to the selection of cases."Publication bias" is about bias observed in published articles.

Question 3

Which of the following statements is not the accurate description of selection bias in case-control studies?

Accepted Answer

Hospitalized patients represent a sample of an ill-defined reference population,not the general reference population.Moreover,hospital patients differ from people in the community.Therefore using hospitalized patients as controls is not the best way to characterize the reference population.The best way to characterize the reference population is using nonhospitalized people as controls with probability sampling from the community (but rarely possible).

Question 4

Which term most accurately describes the following definition? "A study that examines the relationship between diseases (or other health outcomes) and other variables of interest as they exist in a defined population at one particular time." [Porta M,ed.A Dictionary of Epidemiology.New York: Oxford University Press; 2014.]

Accepted Answer

Cross-sectional studies define a population and determine the presence or absence of exposure and the presence or absence of disease for each individual at the same time.Both exposure and disease outcome are determined."Ecologic study" is not correct.Ecologic studies are studies of group characteristics to determine whether an association exists."Case-control study" is not correct.In case-control studies,investigators identify a group of individuals with the disease and a group of individuals without the disease to examine the possible relation of an exposure to a certain disease."Cohort study" is not correct.In cohort studies,investigators select a group of exposed individuals and a group of nonexposed individuals and follows up both groups to compare the incidence of disease in two groups."Randomized trial" is not correct.A randomized trial is a clinical-epidemiologic experiment in which subjects are randomly allocated into groups,usually called test and control groups,to receive or not to receive a preventive or a therapeutic procedure or intervention.

Question 5

A researcher study of Baltimore neighborhoods showed that those with lower median household income experience a higher teen pregnancy rate.After reading this,someone concludes that a teenager with low income is more likely to get pregnant.What is the name of this mistaken conclusion?

Accepted Answer

Ecologic fallacy is making individual-level conclusions from ecologic studies,which collect group-level data.

Question 6

In the paper [Gold E,Gordis L,Tonascia J,et al.Risk factors for brain tumors in children.Am J Epidemiol.1979;109(3):309-319],investigators conducted a case-control study to identify risk factors for brain tumors in children.Children with brain tumors were compared with two groups of controls: The first control group,called normal controls,consisted of children with no known malignant disease.The second control group,called cancer controls,consisted of children with malignancies other than brain tumors.What is the benefit of using multiple controls in case-control studies?

Accepted Answer

Cases are more likely to recall exposures that they believe may have contributed to the outcome.In this case,cancer controls are also likely to remember previous exposures,then we may reduce recall bias."This may reduce the selection bias for participation" might be guaranteed by choosing community controls instead of hospital controls."This may reduce the potential confounders from investigators" is acquired by randomization."This may reduce the placebo effect from participants" is an explanation about blinding (masking) in clinical trial.

Question 7

A group of physicians working in the same hospital noticed a rare presentation of male young patients,free of typical risks factors,who presented to the hospital with rapidly progressing acute kidney failure.They documented their findings and described in detail the progression of disease.What is the study design described here?

Accepted Answer

The study described is a case series,where a group of patients under observation are comprehensively described.It is not a case report because,in this case,multiple patients were identified.

Question 8

To determine the prevalence of smoking among new students in a university,researchers conduct an anonymous survey at the first day of classes.They find that 22% of women and 28% of men were smokers.What type of study design was used?

Accepted Answer

This type of surveys,in which participants are seen once by researchers and several variables are measured at one time point,is called cross-sectional studies.These studies are particularly good to estimate the prevalence of a disease or exposure; for that reason,they are also called "prevalence studies."

Question 9

Which term most accurately describes the following definition? "The observational epidemiological study of persons with the disease (or another outcome variable) of interest and a suitable control group of persons without the disease (comparison group,reference group)." [Porta M,ed.A Dictionary of Epidemiology.New York: Oxford University Press; 2014.]

Accepted Answer

In case-control studies,investigators identify a group of individuals with the disease and a group of individuals without the disease to examine the possible relation of an exposure to a certain disease."Ecologic study" is not correct.Ecologic studies are studies of group characteristics to determine whether an association exists."Cross-sectional study" is not correct.Cross-sectional studies define a population and determine the presence or absence of exposure and the presence or absence of disease for each individual at the same time.Both exposure and disease outcome are determined simultaneously for each subject."Cohort study" is not correct.In cohort studies,investigators select a group of exposed individuals and a group of nonexposed individuals and follows up both groups to compare the incidence of disease in two groups."Randomized trial" is not correct.A randomized trial is a clinical-epidemiologic experiment in which subjects are randomly allocated into groups,usually called test and control groups,to receive or not to receive a preventive or a therapeutic procedure or intervention.

Question 10

Epidemiologists tried to examine the distribution of multimorbidity,and of comorbidity of physical and mental health disorders,in relation to age and socioeconomic deprivation.They extracted data on 40 morbidities from a database of 1,751,841 people registered with 314 medical practices in Scotland as of March 2007.They analyzed the data according to the number of morbidities,disorder type (physical or mental),sex,age,and socioeconomic status.They defined multimorbidity as the presence of two or more disorders.[From Barnett K,Mercer SW,Norbury M,et al.Epidemiology of multimorbidity and implications for health care,research,and medical education.Lancet.2012;380(9836):37-43.] What is the proper classification for this study?

Accepted Answer

Because this study captured all data from 1,751,841 individuals at the same time (with exposure and outcome),cross-sectional study is the most accurate classification of the study."Prospective cohort study" is not correct; they did not follow up the participants."Case-control study" is not correct; they did not classify participants by disease status."Randomized trial" is not correct; they did not randomly allocate exposure status."Case report" is not correct; they did not report a single or series of disease cases.

Question 11

A researcher study of Baltimore's neighborhoods showed that those neighborhoods with lower median household income experienced a higher teen pregnancy rate.What type of study design was used?

Accepted Answer

Ecologic studies are characterized by studying groups of people (in this case,neighborhoods) rather than individuals.

Question 12

Researchers wanted to provide additional support for a causal association between human papillomavirus (HPV) and oropharyngeal cancers.They performed an epidemiologic study of 100 patients with newly diagnosed oropharyngeal cancer and 200 control patients without cancer to evaluate associations between HPV infection and oropharyngeal cancer.[D'souza G,Kreimer AR,Viscidi R,et al.A study of human papillomavirus and oropharyngeal cancer.N Engl J Med.2007;356(19):1944-1956.] What kind of study design is this?

Accepted Answer

Investigators classified participants by disease status,cases,and controls,then investigated the exposure status."Retrospective cohort study" and "Prospective cohort study" are not correct; they did not follow up the participants in either direction."Randomized trial" is not correct; they did not randomly allocate exposure status."Case report" is not correct; they did not report a single or series of disease cases.

Quiz 7: Observational Studies

Which of the following statements is not the accurate description of selection bias in case-control studies?

A researcher study of Baltimore neighborhoods showed that those with lower median household income experience a higher teen pregnancy rate.After reading this,someone concludes that a teenager with low income is more likely to get pregnant.What is the name of this mistaken conclusion?

To determine the prevalence of smoking among new students in a university,researchers conduct an anonymous survey at the first day of classes.They find that 22% of women and 28% of men were smokers.What type of study design was used?

A researcher study of Baltimore's neighborhoods showed that those neighborhoods with lower median household income experienced a higher teen pregnancy rate.What type of study design was used?