Question

1-Non-differential misclassification means that if there is an error in exposure misclassification, it occurs with equal likelihood among diseased and non-diseased individuals.

		True
		False

2-Non-differential misclassification tends to bias study results in which direction?

		Towards the null
		Away from the null
		Either towards or away from the null

3-Selection bias is more likely to occur in studies where

		Only exposure has occurred at the time of subject selection
		Only outcome has occurred at the time of subject selection
		Exposure and outcome have already occurred at the time of subject selection

4-Selection bias is more likely to occur in which type of study?

		Prospective cohort studies
		Retrospective cohort studies
		Case-control studies
		Both retrospective cohort and case-control studies

Answer 1

(1). FALSE

Non-differential classification error is when the error does not depend on the values of other variables.

(2). Away from the Null

Non-differential misclassification tends to bias study results in away from the null direction.

(3). Exposure and Outcome have already occurred at the time of subject selection.

In order for bias to occur, selection has to be related to both exposure and outcome.

(4). Retrospective Cohort studies

Selection bias can occur if selection or choice of the exposed or unexposed subjects in a retrospective cohort study is somehow related to the outcome of interest.