Regression toward the mean: more on the price of beer and the salaries of priests.
Investigators must take great care in studying the temporal association between biological and clinical data. By selecting patients on the basis of deviant levels of a biological parameter, it often is impossible to separate the effect of regression toward the mean from a temporal association of clinical interest. Experimental strategies that focus exclusively on subjects with extreme values are particularly prone to misinterpreting the effects of regression toward the mean as a temporal change in the variable of interest. We cite specific examples of two previous studies of the relationship between the dexamethasone suppression test (DST) and clinical response in depression. Contrary to the conclusions of the investigators, normalization of the DST had no relation to clinical response in the first 5 weeks of treatment. The decrease of post-dexamethasone cortisol levels occurred regardless of clinical response, most likely due to the effect of regression toward the mean.
D000928:Antidepressive Agents / Q000627:therapeutic use; D003866:Depressive Disorder / Q000188:drug therapy / Q000503:physiopathology*; D003907:Dexamethasone; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007030:Hypothalamo-Hypophyseal System / Q000503:physiopathology; D010913:Pituitary-Adrenal System / Q000503:physiopathology; D011569:Psychiatric Status Rating Scales; D012044:Regression Analysis; D013223:Statistics as Topic
D000928:Antidepressive Agents; D003907:Dexamethasone; D006854:Hydrocortisone