Individual differences among students who meet research subject requirements early versus late in the term as a source of sampling bias

The predominant method of recruiting participants for behavioral research in university settings permits students to choose which experiments of many to participate in. When this method is used, the possibility of sampling bias arises because some students make their choices early and others late in the term. This study identified several Q-types (“ideographic” patterns derived from Q-factor analysis) that varied substantially with regard to choice time and thus offered suggestive evidence for a bias thesis. It was recommended that prevalent participant recruitment policy be changed so that experimenters can arrange appointments on a random basis.