The factor structure of SCL-90-R items and scales was analyzed using both exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). Results of CFA studies at the item-level failed to support the original nine-factor model, as well as several alternative models and EFA suggested very different dimensionality, depending on which criteria were used. Analyses at the scale-level (i.e. the nine original symptom dimensions) suggested that a one- or two-factor model was satisfactory according to descriptive goodness of fit criteria. However, using the likelihood ratio test, specification of four factors was necessary to avoid rejection. According to the likelihood ratio test in a multi-group analysis, a lack of factorial invariance across gender was indicated. Moreover, the factorial structure of the instrument was clearly different across levels of negative affectivity (NA); the dimensionality was substantially higher in the low-NA group as compared to the high-NA group. It is concluded that we are confronted with a profound structural indeterminacy problem and that factor analytic methods and model acceptance criteria alone are insufficient to solve this problem. The indeterminacy problem can be accounted for, at least in part, by the complex logical-semantical structure of SCL-90-R items and scales and the role of the NA trait as a structure generating factor.
OBJECTIVE: The study investigated whether results on the Seasonal Pattern Assessment Questionnaire, which is used for diagnosis of seasonal affective disorder, differed by the season in which the questionnaire was completed. METHOD: Every third month from March 1997 to February 1998, a population-based panel of 200 men and women age 27-72 years in Gamvik, northern Norway, completed a standardized questionnaire that included all items from the Seasonal Pattern Assessment Questionnaire. RESULTS: The average score for seasonal affective disorder changed over the year. The difference between the highest score, in March, and the lowest, in September, was 8.8%. CONCLUSIONS: Results on the Seasonal Pattern Assessment Questionnaire varied by season, but did not vary by seasonal differences in the amount of daylight.