Analysis of Covariance: A Delicate Instrument

This review of the advantages and limitations of the analysis of covariance focuses on the assumption the data must satisfy if analysis of covariance is to be a valid technique and includes a description of the effects of unsatisfied assumptions on the covariance procedure and suggestions for checking the validity of the required assumptions. Covariance analysis is compared to adjustments based on between-groups regression and designs incorporating matching or blocking.