To cut a short test even shorter: Reliability and validity of a brief assessment of intellectual ability in Schizophrenia—a control-case family study

Abstract

Background.

The potential inclusion of cognitive assessments in the DSM-V and large time-consuming assessments drive a need for short tests of cognitive impairments. We examined the reliability and validity of a brief, 15-minute, version of the Wechsler Adult Intelligence Scale–III (WAIS-III).

Methods.

The sample consisted of patients diagnosed with schizophrenia (n=75), their siblings without schizophrenia (n=74) and unrelated healthy controls (n=84). A short WAIS-III consists of the Digit Symbol Coding subtest, and every second (or third) item of Block Design, Information, and Arithmetic. Psychometric analyses were implemented using item-response theory (IRT) to determine the best minimal item short version, while maintaining the sensitivity and reliability of the IQ score.

Results.

The proposed 15-minute WAIS-III gave reliable estimates of the Full Scale IQ (FSIQ) in all three groups in the sample. The 15-minute (select-item) version yielded an overall R of.95 (R²=.92) and IRT yielded an R of .96 (R²=.92). All four subtests performed well in differentiating patients, relatives, and healthy controls. Multivariate analysis showed a significant difference in FSIQ-estimate between patients, relatives, and healthy controls, F(2, 202) = 19.00, p < .0001. Regression modelling showed that the three versions of the WAIS had similar associations with functional outcome after a 3-year follow-up.

Conclusions.

Our proposed 15-minute version of the WAIS may serve as a useful screening device for general intellectual ability in research or clinical settings, and is recommended when a quick and accurate IQ estimate is desired.

Keywords:

• Cognitive functioning
• Psychometrics
• Item response theory

We are grateful for the generosity of time and effort by the patients and their families, healthy subjects, and all researchers who make this GROUP project possible.

The infrastructure for the GROUP study is funded by grant 10-000-1002 from the Geestkracht programme of the Netherlands Organisation for Health Research and Development (ZonMw) and matching funds from participating universities and mental health care organisations (Site Amsterdam: Academic Psychiatric Centre AMC, Ingeest, Arkin, Dijk en Duin, Rivierduinen, Erasmus MC, GGZ Noord Holland Noord; Site Utrecht: University Medical Centre Utrecht, Altrecht, Symfora, Meerkanten, Riagg Amersfoort, Delta; Site Groningen: University Medical Center Groningen, Lentis, GGZ Friesland, GGZ Drenthe, Dimence, Mediant, GGZ De Grote Rivieren, and Parnassia Psychomedical Centre; Site Maastricht: Maastricht University Medical Center, GGZ Eindhoven, GGZ Midden-Brabant, GGZ Oost-Brabant, GGZ Noord-Midden Limburg, Mondriaan Zorggroep, Prins Clauscentrum Sittard, RIAGG Roermond, Universitair Centrum Sint-Jozef Kortenberg, CAPRI University of Antwerp, PC Ziekeren Sint-Truiden, PZ Sancta Maria Sint-Truiden, GGZ Overpelt, OPZ Rekem). The GROUP analyses were supported by unrestricted grants from Janssen-Cilag, Eli Lilly & Co., AstraZeneca, and Lundbeck.

EU-GEI is the acronym of the project “European network of National Schizophrenia Networks Studying Gene-Environment Interactions”. The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. HEALTH-F2-2010-241909 (Project EU-GEI).

We are grateful for the generosity of time and effort by the patients and their families, healthy subjects, and all researchers who make this GROUP project possible.

The infrastructure for the GROUP study is funded by grant 10-000-1002 from the Geestkracht programme of the Netherlands Organisation for Health Research and Development (ZonMw) and matching funds from participating universities and mental health care organisations (Site Amsterdam: Academic Psychiatric Centre AMC, Ingeest, Arkin, Dijk en Duin, Rivierduinen, Erasmus MC, GGZ Noord Holland Noord; Site Utrecht: University Medical Centre Utrecht, Altrecht, Symfora, Meerkanten, Riagg Amersfoort, Delta; Site Groningen: University Medical Center Groningen, Lentis, GGZ Friesland, GGZ Drenthe, Dimence, Mediant, GGZ De Grote Rivieren, and Parnassia Psychomedical Centre; Site Maastricht: Maastricht University Medical Center, GGZ Eindhoven, GGZ Midden-Brabant, GGZ Oost-Brabant, GGZ Noord-Midden Limburg, Mondriaan Zorggroep, Prins Clauscentrum Sittard, RIAGG Roermond, Universitair Centrum Sint-Jozef Kortenberg, CAPRI University of Antwerp, PC Ziekeren Sint-Truiden, PZ Sancta Maria Sint-Truiden, GGZ Overpelt, OPZ Rekem). The GROUP analyses were supported by unrestricted grants from Janssen-Cilag, Eli Lilly & Co., AstraZeneca, and Lundbeck.

EU-GEI is the acronym of the project “European network of National Schizophrenia Networks Studying Gene-Environment Interactions”. The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. HEALTH-F2-2010-241909 (Project EU-GEI).