Can we combine symptom scales for collaborative research projects?

Collaborative research projects have the potential to answer important research questions, which may otherwise require huge resources, funding, and time to complete. There are several scales for measuring psychotic symptoms in schizophrenia and other psychotic disorders, with the Scale for Assessment of Positive Symptoms (SAPS), Scale for Assessment of Negative Symptoms (SANS), Positive and Negative Symptom Scale (PANSS), and the Brief Psychiatric Rating Scale (BPRS) being among the most commonly used. High quality research efforts have used these three scales in different projects, and in order to merge study efforts, some means of combining data from these scales may be necessary. We reviewed correlations in published studies for these three scales, finding them to be highly correlated, however on comparison of the three scales there were considerable clinical differences between them. The paper discusses potential methods for combining the scales in collaborative research, including use of the recently developed standardised remission criteria for schizophrenia.