Definition of Stroop interference in volunteers and non-volunteers.

It is proposed that the best measure of individual Stroop interference is the logarithm of the ratio between time to read the interference card and time to read the pure color card, i.e., logs(C/B). A review of the literature shows a very close correlation across studies between Stroop interference so-defined and (un)willingness to participate in psychological experiments, at least for studies involving the Stroop. Logs (C/B) provides a highly reliable index of this effect and should be routinely reported as a sample descriptor. (Pertinent data must be taken from the first administration of the Stroop.) Willingness to volunteer is seen as willingness to take on additional stress; low Stroop interference is seen as high tolerance for such stress.