EPIB exam 2 practice questions
Case-control studies are among the best observational designs to study diseases of:
low prevalence
The Behavioral Risk Factor Surveillance System (BRFSS) collects information on health risks and behaviors annually, through a random digit-dialing system every year. What kind of study design is this?
Cross-Sectional Study
The National Health Interview Survey randomly collects data from approximately 30,000 different households in the United States from year to year. This information is used for both surveillance and research purposes. What study design can this be classified as?
Cross-Sectional Study
Questionnaires were mailed to every 10th person listed in the city telephone directory. Each person was asked to provide his or her age, sex, and smoking habits and to describe the presence of any respiratory symptoms during the preceding 7 days.
Cross-sectional
In a case-control study, cases and controls are selected based on their exposure status.
False
Recall bias describes when participants act differently as a result of being in the study.
False
True or False: Loss to follow up is only a problem in cohort studies.
False
True or False: All cohort studies preserve temporality.
False. Retrospective cohort studies can use retrospective interviews to ascertain information about the exposure. Temporality is not preserved.
Calculate the appropriate measure of association to assess the strength of the relationship between testicular cancer and mother's use of hormones during pregnancy for this study design, and provide an interpretation.
3.77 This is a case-control study, so an OR is the appropriate measure of association. Odds ratio: (90*945) / (55*410) = 85,050 / 22,550 = 3.77
Define the ecological fallacy (1 point). Provide a real-world example (1 point).
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Answer the following questions about odds using data from the table below. Ate watermelon: 72 ill, 4 not ill, total: 77 did not eat watermelon: 115 ill, 112 not ill, 237 in total total ill: 187 total not ill: 127 total: 314
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In a certain noisy factory, workers are given earplugs and are expected to wear them. An industrial hygienist inspecting the plant found that 100 of the 500 workers in the factory were not wearing the earplugs because they regarded them as uncomfortable and as a nuisance. When all the workers were given a hearing test, it was found that 16 of the earplug wearers and 40 of the non-wearers had developed significant hearing loss. All had had normal hearing at their pre-employment exams 1 year earlier, when the plant opened. Complete the contingency table.
...
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. Contingency table
...
In a certain noisy factory, workers are given earplugs and are expected to wear them. An industrial hygienist inspecting the plant found that 100 of the 500 workers in the factory were not wearing the earplugs because they regarded them as uncomfortable and as a nuisance. When all the workers were given a hearing test, it was found that 16 of the earplug wearers and 40 of the non-wearers had developed significant hearing loss. All had had normal hearing at their pre-employment exams 1 year earlier, when the plant opened. Select the correct result for the calculated measure of association.
10
Calculate the odds ratio (OR) in order to complete the sentence below. Individuals who ate watermelon had ___ times the odds of becoming ill relative to those who did not eat watermelon.
14.02
Calculate the odds ratio in order to complete the sentence below. The odds of bone fracture is ______ times higher among sedentary women as compared to non-sedentary women.
2.291
What is the main difference between a prospective cohort study and a retrospective cohort study?
A prospective cohort study is looking at exposure in the present and then following up in the future while a retrospective cohort study uses historical data from the past to determine exposure. So the main difference is is the time period: future vs the past.
To test the efficacy of vitamin C in preventing colds, army recruits are randomly assigned to two groups: one given 500 mg of vitamin C daily, and one given a placebo. Both groups are followed to determine the number and severity of subsequent colds.
Clinical trial
Which of the following criteria need to be met for a variable to be a potential confounder?
Association with exposure Not an intermediate step on the pathway Association with outcome
What is the outcome of interest in this study?
Bone Fracture
Researchers identify 50 cases of individuals with throat cancer, and 50 individuals without throat cancer. The non-cancer participants are matched to the cancer participants by age, sex, zipcode, and race/ethnicity. The researchers then interview all 100 participants about their exposure to batteries. What study design can this be classified as
Case Control Study
An outbreak of COVID-19 occurs at a Whole Foods in College Park, MD, after an employee tests positive. Following contact tracing, an epidemiologist reports 36 cases as a result of this incident. Which study design can this be classified as?
Case Series
Which of the following is NOT an analytic study?
Case Series
Smoking histories are obtained from all patients entering a hospital who have lip cancer and are compared with smoking histories of patients with cold sores who enter the same hospital.
Case control
A hospital identifies 100 patients that died of pancreatic cancer in 2019, and 100 patients that survived pancreatic cancer in 2019. Researchers then consult medical records to investigate whether patients received Drug A or Drug B. What study design can this be classified as?
Case-Control Study
Leprosy, also called Hansen's disease, is a disease produced by infection with a bacterium called Mycobacterium leprae. It has a long incubation period (time between getting infected and developing the disease), usually several years. Leprosy is a disease of low incidence in the United States; only 108 new cases were reported in 1999. If you are called to give advice on the type of study design to be conducted to assess the possible association between several exposures and leprosy, which design do you think would be the best choice?
Case-Control Study
A study was undertaken to test the hypothesis that chewing tobacco increases the risk of stomach cancer. Detailed historical data on chewing tobacco use were collected from 400 subjects with newly diagnosed stomach cancer and 400 subjects without stomach cancer. The subjects without stomach cancer were matched to those with cancer on background characteristics such as age, race/ethnicity and gender. The results revealed that chewing tobacco was not a significant risk factor for stomach cancer.
Case-Control Study This is a case-control study because the participants were selected and matched based on their outcome status. The cases were those with stomach cancer and the controls were as similar as possible to the cases on everything except the presence of the outcome (i.e., no stomach cancer). After participants were selected, their exposure status (e.g., chewing tobacco use) was assessed. Furthermore, the unit of analysis is the individual, and an a priori hypothesis is being tested.
Cohort study is to risk ratio as:
Case-control study is to odds ratio.
In Turkey, it is rumored that several children became infected with influenza by playing with a chicken head. The activities of 20 kids were investigated following the diagnosis of H5N1 influenza in four children (i.e., 4 "cases", 16 "controls"). Of the four children that got sick, three were discovered to have been playing with a chicken head. Among those not sick, eight were discovered to have been playing with the chicken head. Interpret the odds ratio.
Children who played with the chicken head had 3 times the odds of developing influenza relative to children who did not play with the chicken head.
A random sample of middle-aged sedentary women was selected from four census tracts, and each subject was examined for evidence of osteoporosis. Those found to have the disease were excluded. All others were randomly assigned to either an exercise group, which followed a two-year program of systematic exercise, or a control group, which had no exercise program. Both groups were observed semiannually for incidence of osteoporosis.
Clinical trial
A group of researchers would like to examine rates of breast cancer at the state level. What study design can this be classified as?
Ecologic Study
In order to determine if vitamin D (the "sunshine" vitamin) is associated with reduced levels of ovarian cancer, an epidemiologist identified 12 geographic regions in Sweden and obtained data on the average annual number of days of sunlight and ovarian cancer rates for each region. The findings indicated that those regions with the highest average days of sunlight per year had significantly lower rates of ovarian cancer than those regions with the fewest average days of sunlight per year. The epidemiologist reported her findings at the Scandinavian Conference on Cancer.
Ecological Study This is an ecological study because the data used for analysis is group-level data, and the 'groups' are defined by geographic places. The exposure data is the average annual days of sunlight in each region. The outcome data does not come from participants that they selected, it's the average rate of ovarian cancer in each region. There is no intervention being tested, so it's not an experiment or RCT. Furthermore, characteristic of ecological studies, there is an a priori hypothesis (vitamin D is associated with reduced ovarian cancer).
A cross-sectional study allows measurement of the temporal ordering of cause and effect.
False
In a certain noisy factory, workers are given earplugs and are expected to wear them. An industrial hygienist inspecting the plant found that 100 of the 500 workers in the factory were not wearing the earplugs because they regarded them as uncomfortable and as a nuisance. When all the workers were given a hearing test, it was found that 16 of the earplug wearers and 40 of the non-wearers had developed significant hearing loss. All had had normal hearing at their pre-employment exams 1 year earlier, when the plant opened. Select the best interpretation of this measure of association:
Individuals who do not wear earplugs have 10 times the risk of hearing loss relative to those who do wear earplugs.
advantages of randomization
It can control for known confounders It can control for unknown confounders It can ensure comparability between study groups
Which of the following is NOT an advantage of randomization?
It can minimize loss to follow-up
Which of the following is NOT a method for controlling the effects of confounding in epidemiologic studies?
Masking
Calculate the appropriate measure of association to assess the strength of the relationship between testicular cancer and mother's use of hormones during pregnancy for this study design, and provide an interpretation. Provide an interpretation for your measure of association.
Men whose mothers used hormones during pregnancy had 3.77 times the odds of testicular cancer relative to those whose mothers did not use hormones during pregnancy.
In Turkey, it is rumored that several children became infected with influenza by playing with a chicken head. The activities of 20 kids were investigated following the diagnosis of H5N1 influenza in four children (i.e., 4 "cases", 16 "controls"). Of the four children that got sick, three were discovered to have been playing with a chicken head. Among those not sick, eight were discovered to have been playing with the chicken head. calculate odds ratio
Odds Ratio = (A·D) / (B·C) = (3·8) / (8·1) = 3
A study of cancer was conducted among 10,000 men in the United States who were 40-75 years of age. Every two years questionnaires are sent to these individuals, and newly diagnosed cases of various cancers were reported. The investigators in this study were particularly interested in the relationship between physical activity and the development of prostate cancer over a 20 year period. 500 of the 5000 men who were classified as physically active developed prostate cancer, and 1000 of 5000 the men who were classified as not physically active developed prostate cancer. What is the study design?
Prospective Cohort Study
A total of 1,500 adult men who worked for Lockhead Aircraft were initially examined in 1951 and were classified by diagnostic criteria for coronary artery disease. Every three years, they have reexamined for new cases of the disease; attack rates in the different subgroups have been computed annually.
Prospective cohort
The entire population of a given community is examined, and all who are free of covid-19 antibodies are questioned extensively about their behaviors and activities. These people are then followed for several years to see if their behaviors and activities will predict their risk of contracting covid-19.
Prospective cohort
In a certain noisy factory, workers are given earplugs and are expected to wear them. An industrial hygienist inspecting the plant found that 100 of the 500 workers in the factory were not wearing the earplugs because they regarded them as uncomfortable and as a nuisance. When all the workers were given a hearing test, it was found that 16 of the earplug wearers and 40 of the non-wearers had developed significant hearing loss. All had had normal hearing at their pre-employment exams 1 year earlier, when the plant opened. What is the design of the study described above?
Prospective cohort study
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. What is the design of the study described above?
Prospective cohort study
Based on your calculations, is physical activity a protective or risk factor for prostate cancer?
Protective Factor Because the RR <1, physical activity is considered a protective factor against prostate cancer. Individuals that engage in physical activity have a lower risk of prostate cancer relative to individuals that do not engage in physical activity.
Interpret the following values. Please check with your TA if your answer does not match the key here, but you believe it is a variation of the correct answer.
RR = 1.0: The risk of the outcome among the exposed is not different from the risk of the outcome among the non-exposed. RR = 0.5: The risk of the outcome among the exposed is 0.5 times the risk of the outcome among the non-exposed. RR = 2.0: The risk of the outcome among the exposed is two times the risk of the outcome among the non-exposed. OR = 1.0: The odds of the outcome among the exposed are not different from the odds of the outcome among the non-exposed. E. OR = 0.1: The odds of the outcome among the exposed is 0.10 times the odds of the outcome among the non-exposed. OR = 5.0: The odds of the outcome among the exposed is five times the odds of the outcome among the non-exposed.
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. Calculate this measure of association using the given data.
RR = [A/(A+B)] / [C/(C+D)] = [8/(8+92)] / [20/(20+180)] = 0.08 / 0.1 = 0.8
To see if hypnosis could reduce chronic pain, investigators randomly assigned 120 volunteers with osteoarthritis to either hypnosis therapy or standard treatment. Pain levels were checked among the subjects every three months during the 12-month study using validated pain measures. Those assigned to the hypnosis group reported reduced pain compared to those in the standard treatment group after three and six months, but not after nine and 12 months, of follow up.
Randomized Controlled Trial This is a randomized controlled trial because the subjects are randomly assigned to experimental and control groups (i.e., there is an intervention), and the unit of analysis is the individual. Furthermore, characteristic of randomized controlled trials, exposure status is assigned prior to determining outcome status.
The investigators in this study used in-person interviews in order to gather information about the exposure status of the cases and controls. What is one major limitation of this method for assessing exposure status in this situation?
Recall Bias
The investigators in this study used in-person interviews in order to gather information about the exposure status of the cases and controls. What is one major limitation of this method for assessing exposure status in this situation?
Recall or reporting bias
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. Considering the design of the study, a _______________ is the most appropriate measure of association to characterize the relationship between the exposure (e.g., eating a vegetarian diet) and the outcome (e.g., developing heart disease).
Relative Risk, because this is a cohort study (i.e., we know the population at-risk, and the defined time period during which new cases developed, so we can calculate incidence, therefore we use RR).
Based on the data in the table, calculate the appropriate measure of association between physical activity and prostate cancer.
Relative risk is the appropriate measure for a cohort study. RR = ((500/5000)/(1000/5000))=0.5
Compared to other study designs, what is unique about an experimental design?
Researchers assign the exposure of interest to participants..
The Nurses' Health Study is a prospective cohort study that follows female nurses, aged 25-42. Which of the following techniques does this study use to minimize confounding?
Restriction
A total of 825 insulation workers employed between 1951 and 1955 was identified from the personnel records of three large insulation manufacturing plants in the southeastern U.S. in 1995. During the period 1951-1995, 26 deaths from lung cancer were discovered among the workers. Only six lung cancer deaths, however, were reported among a comparable group of 700 coworkers who did not work with insulation during the same time period. The investigators had postulated that exposure to the insulation material increases the risk of lung cancer.
Retrospective Cohort Study This is a retrospective cohort study because a group of people is identified and information was collected up to the time of the study initiation. This study is retrospective because it "started" in 1995, but all data used were collected before 1995 (e.g., 1951-1995). If it were prospective, the data collection would begin with the study start date and move forward over time Also, it is not experimental since there is no intervention, and the investigators do not have direct control of the subjects' exposure status. It is not a case-control study because the study subjects are not selected based on the presence or absence of the outcome.
The physical examination records of the incoming class of 1935 at UMD are examined in 1980 to see whether the freshmen's recorded height and weight at the time of admission to the university were related to their chance of developing coronary heart disease by 1981.
Retrospective cohort
Which type of cohort study design is best when the disease has a long latency and/or induction period?
Retrospective cohort
In a certain noisy factory, workers are given earplugs and are expected to wear them. An industrial hygienist inspecting the plant found that 100 of the 500 workers in the factory were not wearing the earplugs because they regarded them as uncomfortable and as a nuisance. When all the workers were given a hearing test, it was found that 16 of the earplug wearers and 40 of the non-wearers had developed significant hearing loss. All had had normal hearing at their pre-employment exams 1 year earlier, when the plant opened. What measure of association is appropriate, given the study design that you selected above?
Risk ratio
Read the news coverage of the Illinois Workplace Wellness Study (PDF article linked). Do you have more confidence in the results from the RCT analysis or observational analysis (1 point)? Provide a rationale for your answer (2 points).
Sample response: I would have more confidence in the results of the RCT analysis relative to an analysis of the observational data. This is because randomization of the study exposure eliminates confounding and allows us to isolate the impact of the exposure on the study outcome.
What is the exposure of interest in this study?
Sedentary Lifestyle
The healthy worker effect is a form of what type of bias?
Selection bias
Which of the following is a method for controlling confounding in the analysis phase only of a study?
Stratification
Cohort effect
The influence of membership in a particular cohort.
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. What is a limitation of using a prospective cohort study for the study discussed above?
The study will take a long time, and is at risk for losing contact with participants over time
Cohort analysis
The tabulation and analysis of morbidity or mortality rates in relationship to the ages of a specific group of people (cohort) identified at a particular period of time and followed as they pass through different ages during part or all of their life span.
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. Complete the phrase below to write the null hypothesis for the study described above: There is _______ difference between vegetarians and non-vegetarians in the occurrence of heart disease.
There is no difference between vegetarians and non-vegetarians in the occurrence of heart disease.
You are investigating the role of physical activity in heart disease and suggest that physical activity protects against having a heart attack. While presenting these data to your colleagues, someone asks if you have thought about confounders such as factor X. This factor X could have confounded your interpretation of the data if it:
is a factor associated with physical activity and heart disease.
purposes of randomization
To ensure that treatment is assigned in an unbiased fashion To ensure comparability between treatment groups To minimize confounding
Which of the following is NOT a purpose of randomization?
To match on exposure
The term attributable risk is also known as the rate difference or risk difference.
True
True or False: Exposure-based cohort studies permit investigations of exposures that are uncommon.
True
True or False: The counterfactual ideal comparison group for a cohort study would consist of exactly the same individuals in the exposed group had they not been exposed.
True
Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. Interpret the result you calculated in a single sentence.
Vegetarians had 0.8 times the risk of heart disease relative to those who are not vegetarians.
In Turkey, it is rumored that several children became infected with influenza by playing with a chicken head. The activities of 20 kids were investigated following the diagnosis of H5N1 influenza in four children (i.e., 4 "cases", 16 "controls"). Of the four children that got sick, three were discovered to have been playing with a chicken head. Among those not sick, eight were discovered to have been playing with the chicken head. Why can't we calculate a risk ratio in this study?
We do not have information on the incidence in the population, therefore we cannot compute the incidence rates required to estimate relative risk in the eligible population.
cohort
a population group, or subset thereof, that is followed over time
T/F: Loss to follow up can be a problem in cohort studies but not experimental studies.
false
True or False: Observational studies suffer the same ethical and feasibility issues as experimental studies.
false
Interviewer bias can occur in:
any type of epidemiologic study.
For a variable to be a confounder, it must be:
associated with the disease (outcome) under study. and associated with the risk factor (exposure) under study
Loss to follow-up bias is an important concern in which type of epidemiologic study?
both cohort and experimental studies
name that study design: A study was undertaken to test the hypothesis that chewing tobacco increases the risk of stomach cancer. Detailed historical data on chewing tobacco use was collected from 400 subjects with newly diagnosed stomach cancer and 400 subjects without stomach cancer. Participants without stomach cancer were matched to those with cancer on background characteristics such as age, race/ethnicity and gender. The results revealed that chewing tobacco was not a significant risk factor for stomach cancer.
case-control study
NAME THAT STUDY: A community assesses a random sample of its residents by telephone questionnaire. Participants are asked to report their height, weight and the presence of any current health conditions (e.g., hypertension, diabetes). Findings indicate that obesity is strongly associated with diagnosed diabetes.
cross-sectional
Which of the following studies does NOT use individuals as the unit of analysis?
ecological study
name that study design: An epidemiologist tested the hypothesis that vitamin D (i.e., the "sunshine" vitamin) is associated with reduced levels of ovarian cancer using data from 12 geographic regions in Sweden. The association was measured using the average annual number of days of sunlight and the rate of ovarian cancer in each region. The findings indicated that the regions with the highest average days of sunlight per year had significantly lower rates of ovarian cancer than those regions with the fewest average days of sunlight per year. The epidemiologist reported her findings at the Scandinavian Conference on Cancer
ecological study
Please select all that apply. A double-masked study of a vaccine is one in which:
neither observers nor subjects know which subject receives the vaccine and which receives a placebo.
A cohort study of liver cancer among men with unhealthy alcohol use. Incidence rates of liver cancer among men with unhealthy alcohol use are compared to a group of men who are non-drinkers. Is gender a confounder in this study?
no
2x2 table ^^^
physically active: 500 have prostate cancer, 4500 have no prostate cancer, 5000 total not physically active: 1000 have prostate cancer, 4000 have no prostate cancer, 5000 total
name that study design: Study investigators invited all male physicians in the UK to fill out questionnaires regarding their health status and their smoking status. They then focused on the healthy physicians who were willing to participate and mailed follow-up questionnaires to them every 2 years. Using death certificate data the researchers noted the cause of death for any subjects who became ill and died. The study continued for 50 years
prospective cohort study
Name that study design: To see if hypnosis could reduce chronic pain, investigators randomly assigned 120 volunteers with osteoarthritis to either hypnosis therapy or standard treatment. Pain levels were checked among the subjects every three months during the 12-month study using validated pain measures. Those assigned to the hypnosis group reported reduced pain compared to those in the standard treatment group after three and six months, but not after nine and 12 months of follow up.
randomized controlled trial
Name that study design: In 1995 researchers obtained the personnel and health records from two large insulation factories in the southeastern U.S. The records showed that between 1951 and 1955 there were 825 workers employed at Factory A, and 700 workers employed at Factory B. Between1951-1994 there were 26 deaths from lung cancer among the workers from Factory A, where asbestos was used in production. During the same time period there were only six lung cancer deaths, among the workers from Factory B, where asbestos was not used in production. The investigators hypothesized that exposure to asbestos was associated with an increased risk of lung cancer.
retrospective cohort study
A case-control study was designed to test the hypothesis that sedentary lifestyle (i.e., no exercise) increases the risk of bone fractures (the outcome) in elderly women. Of the 600 women studied (200 cases and 400 controls), 128 were regular exercisers (26 cases and 102 controls). Based on this information, determine if sedentary lifestyle is a risk factor for bone fractures in this group. Fill in the following table, and use the information to complete questions 5-8.
sedentary lifestyle: 174 bone fractures, 298 no bone fractures, total: 472 no sedentary lifestyle: 26 bone fractures, 102 no fractures, total: 128 total bone fractures: 200 total no bone fractures: 400 total: 600
Which of the following studies is an example of a population-based cohort study?
tecumseh study, framingham study and iowa womens health study
A study must be valid before its results can be generalized.
true
An ecologic study is one that examines a group as a unit of analysis.
true
A case-control study of the risk of beer consumption and oral cancer among men. In this study, cigarette smoking is associated with beer consumption and is a risk factor for oral cancer among both beer drinkers and nondrinkers. Is cigarette smoking a confounder in this study?
yes
Consider each of the following scenarios and state whether or not the variable in question is a confounder. A study of the risk of pulmonary hypertension among women who take diet drugs to lose weight. The crude relative risk of pulmonary hypertension comparing diet drug users to non-users is 17.0 and the age adjusted relative risk is 5.0. Is age a confounder in this study?
yes
