Examining the Psychometric Properties and Factor Structure of the Psychosis Screening Questionnaire Among South African Adults

Abstract

Background: Psychotic experiences are common and often transient but can herald the development of a psychotic disorder. Although early detection of psychosis improves treatment outcomes, there is limited research evaluating the validity of psychosis screening instruments, particularly in low- and middle-income countries.

Objective: To assess construct validity and psychometric properties of the Psychosis Screening Questionnaire (PSQ) in South Africa.

Methods: The sample consisted of 2591 South African adults participating as controls in a multi-country case-control study of psychiatric genetics. We used confirmatory factor analysis and item response theory to evaluate the psychometric properties of the PSQ.ResultsThe average age of participants was 35 years (SD= 11.7), with slightly more female (52%) participants. Approximately 11% of the participants endorsed at least one psychotic experience on the PSQ, and almost half of them (49%) occurred within the last 12 months. A unidimensional model demonstrated good fit (root mean square error of approximation (RMSEA) = 0.023; comparative fit index (CFI) = 0.977; and Tucker-Lewis Index (TLI) = 0.954). Of the different symptoms, mania had the weakest association with a single latent factor (standardized factor loading 0.14). Model fit improved after removing the mania item (RMSEA = 0.025; CFI = 0.991; TLI = 0.972). When the mania item was excluded from IRT analysis, the PSQ provided more information at higher latent trait levels (psychosis).

Conclusion: Consistent with prior studies in other settings, the PSQ demonstrated a unidimensional factor structure among South Africans. However, our findings suggest that the PSQ as a screen for psychosis performs better without the mania item. Future studies that examine the criterion validity of the PSQ are warranted.

Note:

Funding Information: This research was supported by the Stanley Center for Psychiatric Research at Broad Institute of MIT and Harvard and the National Institutes of Mental Health (NIMH) [ grant number 1R01MH120642]. BG, DJS, AS, RES are supported in part by NIMH [grant numbers R01MH120642]. AA was supported by NIMH [grant number T32MH017119].

Declaration of Interests: None.

Ethics Approval Statement: Ethical approval to conduct this study was obtained from all participating sites, including the University of Cape Town Human Research Ethics Committee (REF# 466/2016), the Western Cape Government (WC_2016RP32_349), and the Walter Sisulu University Research and Ethics Committee (SOMREC #REC REF 2016-057) in South Africa and the Harvard T.H. Chan School of Public Health (#IRB17-0822) in the United States. All experimental protocols were approved by the above-named institutions and/or ethics committees. Informed consent was obtained from all study participants and all experiments were conducted in accordance with the relevant guidelines and regulations.

Keywords: psychosis, Assessment, psychosis screening questionnaire, South Africa