So Basic
The Cancer Prevention Study Nutrition Cohort, in which researchers enrolled ~184,000 men and women in 1992 and collected exposure and lifestyle information to assess the relationship between these factors and subsequent occurrence of cancer, is an example of which type(s) of study?
Prospective cohort study
Controlling or adjusting for confounding can be achieved by conducting stratified analyses and using one of several adjustment methods. What is more often used and preferred?
Modeling
What are the two types of error we are concerned about in epidemiologic studies?
Random and systematic error
What measures are used to describe the accuracy of a test and give the probability of a correct test result given disease status?
Sensitivity and specificity
______________ occurs when the measure of association is distorted because it is mixed with the effect of an extraneous factor that is not balanced between comparison groups
Confounding
British investigators conducted a study to compare measles-mumps-rubella (MMR) vaccine history among 1,294 children with pervasive development disorder (e.g., autism and Asperger's syndrome) and 4,469 children without such disorders. (They found no association.) This is an example of which type of study design?
Case-control study
A simple analysis only contains information on what variables?
Exposure and disease
What are the three types of systematic error/bias in the design, conduct, or analysis that results in an incorrect (biased) estimate of a measure of association?
Selection bias
Information bias
Confounding
What measures are used to estimate probability of disease given the test result that vary by prevalence of disease?
Positive predictive value (PPV) and negative predictive value (NPV)
What are the three a prior criteria for assessing confounding?
1. A confounder must be a risk factor for the disease (not caused by it).
2. A confounder must be associated with the exposure.
3. A confounder cannot be an intervening variable between the exposure and the outcome.
In a study of 6,594 men from the Atherosclerosis Risk in Communities study without a cancer history at enrollment in 1987-89, aspirin use was inversely associated with case-fatality (HR: 0.45, 95% CI: 0.22-0.94). Was the measure of association statistically significant?
Yes. The null value (1) is not included in the 95% CI (0.22-0.94) so the estimate of association is statistically significant.
BONUS: Is the corresponding p-value <0.05 or >=0.05?
What do we call models that contain one dependent variable (the outcome) and multiple independent variables (exposure and covariates)?
Multivariable models
If the observed association is an overestimation of the truth, what direction is the bias?
Away from the null
What do sensitivity and specificity need to be for outcome misclassification to be considered non-differential?
Sensitivity (exposed) = Sensitivity (unexposed)
Specificity (exposed) = Specificity (unexposed)
In a study examining the association between alcohol and coronary heart disease, the crude risk ratio was found to be 2.15. After adjusting for smoking status, the risk ratio attenuated to 1.75. Is there evidence for confounding by smoking?
Yes. % difference = 22.9%
A group of 20 friends went to a restaurant. The next day, 7 were ill. Among those who got ill, 5 ate fish while only 3 of the friends who did not get ill ate fish. Calculate the appropriate measure of association for the association between fish consumption and gastrointestinal illness.
OR=(5x10)/(2x3)=8.33
In a survival analysis, individuals may no longer be at risk for the event of interest for what reasons?
Censored, died, or got the event of interest (if the event of interest is not death)
Selection bias in a cohort/RCT can occur by:
1)In the way that subjects are selected from the source population into the study population AND/OR
2) ?
Selective losses from the study population prior to data analysis (aka loss to follow-up)
BONUS: How may selection bias impact a case-control study?
A new screening test for glaucoma was developed and administered to 1,000 adult volunteers at a large medical clinic. These subjects also underwent a comprehensive ophthalmologic exam (the gold standard).
Among study participants, 16% were determined to have glaucoma by ophthalmologic exam.
Of 722 individuals classified as disease-free based on the new screening test, 714 were also classified as disease-free based on ophthalmologic examination. Calculate sensitivity and specificity.
Sensitivity = 152/160 = 95%
Specificity = 714/840 = 85%
What measures of association are used when examining additive interaction?
Risk or rate differences
Additive interaction describes differences in stratum-specific difference measures of association (e.g., RD)
Why is it preferable to enroll incident cases rather than prevalent cases in a case-control study?
If exposure is associated with decreased survival, we may miss many exposed cases and underestimate the true relationship between exposure and disease
BONUS: What type of bias is this?In 1987, 61 patients with pancreatic cancer with a Whipple resection were randomized to be given either intravenous (IV) treatment with 370 mg of monoclonal antibody (MoAb) or no additional anti-cancer treatment. In the first month, 5 patients in the treatment group and 6 patients in the control group died. What was the probability of surviving the first month of the trial?
In a case-control study of diabetes and pneumonia, the cases were people hospitalized for pneumonia while controls were selected from DMV records. What special kind of selection bias may this introduce?
Berkson's bias
BONUS: If pneumonia cases are more likely to be hospitalized if they also have diabetes, in what direction might this bias the measure of association?
A new screening test for glaucoma was developed and administered to 1,000 adult volunteers at a large medical clinic. These subjects also underwent a comprehensive ophthalmologic exam (the gold standard).
Among study participants, 16% were determined to have glaucoma by ophthalmologic exam.
Of 722 individuals classified as disease-free based on the new screening test, 714 were also classified as disease-free based on ophthalmologic examination. Calculate PPV and NPV.
PPV = 152/278 = 54.7%
NPV = 714/722 = 98.9%
In a case-control study examining the effect of XRCC3-T241M polymorphisms and various environmental factors on breast cancer, the OR for the M/M genotype was 1.47 (95% CI: 1.00-2.15) compared to the T/T genotype. However, when the effect was examined in combination with alcohol consumption, it was found that the OR for the M/M genotype was 1.21 (0.70-2.09) among non-drinkers and 2.09 (1.16-3.78) among drinkers of alcohol compared to non-drinkers with the T/T genotype. What do these results suggest? How do you proceed?
It seems that the XRCC3-T241M polymorphism does not have much of an effect unless in combination with alcohol, suggesting interaction. We would proceed with a test for interaction (Breslow-Day) and report stratum-specific ORs if the results were statistically significant.
BONUS: On what scale is there interaction?