Psychometric properties of the credibility/expectancy questionnaire.

The present research evaluated the psychometric properties of the credibility/expectancy questionnaire, a quick and easy-to-administer scale for measuring treatment expectancy and rationale credibility for use in clinical outcome studies. The results suggested that this questionnaire derives the two predicted factors (cognitively based credibility and relatively more affectively based expectancy) and that these factors are stable across different populations. Furthermore, the questionnaire demonstrated high internal consistency within each factor and good test-retest reliability. The expectancy factor predicted outcome on some measures, whereas the credibility factor was unrelated to outcome. The questionnaire is appended to the paper, yet the authors stress care when utilizing the scale. During the administration of the questionnaire, the participant sees two sections--one related to thinking and one related to feeling. However, the researcher needs to be aware that the 2 factors derived are not grouped into those questions. Instead credibility was found to be derived from the first three think questions and expectancy was derived from the fourth think question and the two feel questions.