Some problems concerning the reliability and structure of the scales in the Inpatient Multidimensional Psychiatric Scale (IMPS)

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Abstract
Two problems concerning the IMPS are revealed. First, the importance of an appropriate reliability measure is demonstrated in a sample of 124 inpatients. Widely divergent results are found using three different intraclass correlation coefficients. The one producing the highest results was used by Klett and McNair (1966) and by Behrends et al. (1971). However, the results from this measure only apply to certain types of investigation. A measure more applicable to most investigations in psychiatric research (the intraclass correlation coefficient of individual ratings with between-rater variance included) produced results that were clearly lower, although still acceptable, with an average correlation of 0.72 between the 12 scales. Secondly, the multiplication of item scores by 2 or 8 when forming the scale scores is shown to lead to unusual and undesirable scale distributions in a sample of 1932 inpatients. The resulting implications for assessing change scores on some of the IMPS scales are discussed.