Contrast Variable for Group Comparisons in Biopharmaceutical Research

Abstract

Group comparisons can be conducted at three levels: (1) group means, (2) both group means and variabilities, and (3) group distributions. A traditional contrast is defined as a linear combination of group means; thus, traditional contrast analysis may only effectively address group comparisons in the first level. The concept of a contrast variable has recently been proposed. A contrast variable is defined as a linear combination of random variables (each variable representing random values in a group) instead of group means. Based on a contrast variable, we can use the mean of a contrast to address questions on group comparisons at the first level as in traditional contrast analysis. Meanwhile, we can use the ratio of mean to standard deviation of a contrast variable, that is, standardized mean of a contrast variable (SMCV), to effectively address questions at the second level. We can further use the probability that a contrast variable obtains a positive value, that is, c +-probability, to effectively address questions at the third level. In this article, we explore the use of contrast variable, SMCV, and c +-probability for comparing multiple groups in biopharmaceutical studies. Contrast variable, c +-probability, and SMCV are applicable in a comparison context with or without independence and with or without homoscedasticity.