The schedule for Schizotypal Personalities (SSP): a diagnostic interview for schizotypal features

The validity and reproducibility of psychiatric diagnosis are crucial to psychiatric research. To establish confidence in assigning schizotypal features, three paradigms estimating the reliability of a new instrument, the Schedule for Schizotypal personalities (SSP), were tested. The first paradigm considered joint, but independent evaluations made by two raters simultaneously. The second paradigm assessed evaluations on different occasions, with a mean interim time of 5.9 months (test-retest procedure). Both reliability paradigms demonstrated high levels of agreement for all of the scaled items. Ninety percent of the intraclass correlation coefficients were 0.80 or better for the joint evaluations, and 70% were 0.80 or better for the test-retest evaluation. The third paradigm measured the reliability of DSM-III Schizotypal Personality Disorder. The kappa value for measuring diagnostic agreement was 0.88. The authors recommend the use of the SSP as an interview schedule and discuss the implications of their findings for genetic and biological research of schizophrenia spectrum disorders.