Ef. Halpern, INADEQUACY OF SAMPLE SIZES IN CLINICAL-TRIALS OF LABORATORY PARAMETERS ATTRIBUTABLE TO INVALID STATISTICAL ASSUMPTIONS, Clinical pharmacology and therapeutics, 56(4), 1994, pp. 437-444
Clinical trials often determine the sample size based on the use of st
atistical methods such as analysis of variance, t tests, and rank sum
tests, which compare mean or median values. The resulting studies rare
ly are big enough to show that the method is based on mistaken assumpt
ions. Data from a recent clinical trial of nephrotoxicity associated w
ith the use of contrast agents during angiography found a significant
difference on the order of the difference that previous studies had in
tended to detect. It also showed that a central assumption does not ap
ply to changes in serum creatinine. As a result, the previous studies
had considerably lower power than believed. Their lack of significance
reflected only the mistaken assumption. Analysis of variance, t tests
, and rank sum tests may be just as invalid for other clinical paramet
ers. Lack of significance cannot be automatically taken to imply a sma
ll treatment effect.