SITUATIONAL EFFECTS IN TRAIT ASSESSMENT - THE FPI, NEOFFI, AND EPI QUESTIONNAIRES

While most researchers do agree now that situations may, have an effec t in the assessment of traits, the consequences have been neglected, s o far: if situations affect the assessment of traits we have to take t his fact into account in studies on reliability and validity of measur ement instruments and their application. In the theoretical part of th is article we provide a more formal exposition of this point, introduc ing the basic concepts of latent state-trait (LST) theory. LST theory and the associated models allow for the estimation of the situational impact on trait measures in non-experimental, correlational studies. I n the empirical part, LST theory is applied to three well known trait questionnaires. the Freiburg Personality Inventory, the NEO Five-Facto r Inventory and the Eysenck Personality Inventory. It is shown that si gnificant proportions of the variances of the scales of these question naires are due to situational effects. The following consequences of t his finding are discussed. (i) Instead of the reliability coefficient, the proportion of variance die to the latent trait, the consistency c oefficient, should be used for the estimation of confidence intervals for trait scores. (ii) To reduce the situational effects on trait esti mates it may be useful to base such an estimate on several occasions, ie., to aggregate data across occasions. (iii) Reliability and validit y, studies should not only be based on a sample of persons representat ive of those to whom the test will be applied they should also be cond ucted in situational contexts representative of the intended applicati ons.