Construct and discriminant validity and dimensionality of the Interview Schedule for Social Interaction (ISSI) in three psychiatric samples

This study was aimed at investigating the psychometric properties of the Interview Schedule for Social Interaction (ISSI), in terms of construct and discriminant validity and unidimensionality, in three psychiatric samples with varying prerequisites for social interaction: 1) an outpatient sample of working age with mixed diagnoses, 2) an outpatient sample with schizophrenia, and 3) an inpatient sample composed of mentally ill, male offenders. The target constructs were psychosocial functioning and satisfaction in different life domains. It was hypothesized that the ISSI would mainly be related to psychosocial functioning and life domains characterized by social interaction, such as friends and family. A second hypothesis was that the ISSI ratings would discriminate between the three samples. The first hypothesis was confirmed, but the pattern of relationships was somewhat different between the groups. Whereas family contacts were of great importance for social integration in Samples 1 and 2, friends seemed more important for the mentally ill offenders. The second hypothesis was partly confirmed: three ISSI sub-scales out of four discriminated between the samples. Moreover, the ISSI proved to be a unidimensional construct. The support for the four proposed sub-scales was not unanimous, however, and the sub-scales targeting attachment constituted less stable factors. This study demonstrated the construct and discriminant validity of the ISSI when applied to samples with various mental disorders. The fact that similar results were obtained in all three samples, despite varying prerequisites for social interaction, strongly supports the validity of the ISSI. Providing the sub-scales are used with caution, the ISSI seems to be a reliable tool for use with patients with severe mental disorders.