The presence of artifactual bias in analysis of covariance (ANCOVA) and in matching nonequivalent control group (NECG) designs was empirically investigated. The data set was obtained from a study of the effects of a television program on children from three day care centers in Mexico in which the subjects had been randomly selected within centers. However, differences in the scores of the children between centers were sufficient to provide a more able and a less able group for subsamples in an artificial quasiexperimental study of the same variables. With these subsamples, the same treatment effects were estimated using each NECG design. Unbiased and NECG estimators were then compared for each design, using the one-tailed binomial test to seek the presence of a systematic artifactual bias. A significant bias underrating the group initially lower on the pretest measures was found in both designs. The use of modern multivariate analysis designs was recommended as a better alternative, but experimental studies of these designs were also recommended. The advantage of randomization and true experimental design was pointed out. (Author/CTM)