Please no guesses! I will rate fairly and quickly!
In a case-control study of smoking and lung cancer, researchers are concerned because
participation rates were lower among eligible controls than among eligible cases (i.e., patients
with lung cancer were more willing to participate in the study). When the researchers compared
smoking rates among study participants and those who refused to participate, however, they
found that rates were similar. What threat to validity is described in this scenario, if any? No
threat Measurement bias Nondifferential misdassification of outcome Sampling error Selection
bias A small cohort study of exercise and gestational diabetes (diabetes that developes during
pregnancy) found that rates of gestational diabetes were not significantly different among women
with low exercise levels as compared to women with high exercise levels (p=0.18). What threat

to validity is described in this scenario, if any? Select one: Measurement bias Sampling error
Solution
1-: C
2-: A
Non differential misclassification is when all classes, groups, or categories of a variable (whether
exposure, outcome, or covariate) have the same error rate or probability of being misclassified
for all study subjects. The traditional assumption has been that, in the case of binary or
dichotomous variables, this would result in an underestimate of the hypothesized relationship
between exposure and outcome. This has more recently been challenged however in that results
of individual studies represent a single estimate and not the average of repeated measurements
and thus can be farther (or nearer) from the null value (i.e. zero) than the true value.