Iterative Construction of Nearly Balanced Assignments I: Categorical Covariates

Abstract

A new design criterion, called the B criterion, is given for the situation where each experimental unit has some (categorical) covariate information. It directly addresses the question of balanced assignment over covariates, is simple in form, and does not involve matrix inversion. A simple and efficient algorithm for generating nearly baianced assignments is given. The basic element of the algorithm consists of switching and exchanging treatment assignments. The algorithm is illustrated on two examples.

KEY WORDS:

• Covariate adjustment
• Imbalance measure
• Maximal balance
• Nearly Boptimal assignment
• Switch and exchange routine