Psychometric properties of the Social knowledge test (SKT) and the Combined stories test (COST) in people with a schizophrenia spectrum disorder.

Background: People with schizophrenia spectrum disorders (SSD) often present with impaired social cognition. Among the measures available to assess these deficits, the Combined stories test (COST) and the Social knowledge test (SKT), that respectively target theory of mind (ToM) and social knowledge, have shown promising psychometric properties in prior studies. Test-retest reliability was however only examined in the general population, and the acceptability of these tests was not previously examined. This study aimed to further document the psychometric properties of the COST and the SKT and the acceptability of these tests in people with SSD and community controls (CO). Methods: Forty-four (44) participants with SSD and 49 CO were administered the COST and SKT twice, about 4 weeks apart, and were asked to rate the acceptability of the tests on a 0 (Very unpleasant) to 10 (Very pleasant) point scale at both timepoints. Results: In both groups, the results revealed an excellent inter-rater reliability and a good test-retest reliability for both tests, though the control non-social reasoning measure included in the COST showed poorer test-retest reliability in the SSD group. Some practice effects were observed but the ToM score from the COST and the SKT total score showed no evidence of ceiling effects at either timepoints. The average acceptability scores ranged between 7.8/10 and 8.3/10 for the COST and between 6.8/10 and 7.9/10 for the SKT. Conclusion: The SKT and the COST present with good psychometric properties, representing good options for future studies or for use in clinical practice.