Disease based spectrum bias in referred samples and the relationship between type A behavior and coronary artery...

Using referred samples to study predictors of disease produces statistical problems that reduce the likelihood of obtaining statistically significant results even when a substantial relationship is present between a risk factor and a disease. The present paper refers to these problems as disease based spectrum (DBS) bias. DBS bias is present when subjects are directed into or excluded from the study sample according to their disease status. For example, healthy individuals are excluded from and diseased individuals are directed into referred samples. Therefore, DBS bias is present in referred samples. Examples from the literature on Type A behavior and coronary artery disease (CAD) are presented to illustrate how DBS bias reduces statistical associations. The results of the current research indicate DBS bias has reduced the association between Type A behavior and CAD in a number of studies reported in recent years. In addition, the present article discusses techniques for assessing and controlling for DBS bias.