HSCI 330 Lecture Notes - Lecture 5: Odds Ratio, Clinical Trial, Cohort Study
16 Jan 2019
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Selection bias can occur from systematic error that results from the way subjects are selected into the study and remain for analysis. The primary reason for such bias usually differs with the type of study used. In case-control studies, the primary source of selection bias is the manner in which cases, controls, or both are selected. Suppose patients assigned to the new treatment are more likely than those on the standard to develop side effects and consequently withdraw from the study. In cross-sectional studies, the primary source of selection bias is what is called selective survival. Consequently, the bias would be away from the null. The proportion exposed among diagnosed cases selected for study is likely to be ??? the proportion exposed among all cases in the source population. larger than: smaller than, equal to. Clinical trial: new cancer regimen versus standard regimen. Only survivors can be included in cross-sectional studies.
