Top-down purification of Tobacyk's Revised Paranormal Belief Scale

Using mostly undergraduate student data (N = 560), factor analysis confirmed the existence of seven factors in Tobacyk's Revised Paranormal Belief Scale (RPBS). However. this replication proved to be of dubious value since (1) the factor structure was significantly affected by age and gender; (2) the items in Tobacyk's original factors were significantly non-additive; (3) the items showed pervasive differential item functioning (DIF) related to respondents' ages, gender, or both; and (4) simulations indicated that the factor structure are the result of DIF. The removal of DIF via "top-down purification" yielded two correlated clusters of items dubbed "New Age Philosophy" and "Traditional Paranormal Beliefs". Both clusters obey an Andrich rating-scale model with person reliabilities of 0.90 and 0.74, respectively. Principal component analysis confirmed that these two clusters are unidimensional and without significant age or gender DIF (p > 0.10), While the Traditional Paranormal Beliefs cluster continued to show a significant main effect of age, neither cluster showed a significant gender effect, thereby calling into question some traditional findings regarding paranormal beliefs. We strongly suspect that the dearth of DIF studies indicates that age and gender biases due to DIF have largely gone unnoticed in the extant personality and assessment literature. (C) 2000 Elsevier Science Ltd. All rights reserved.