BACKGROUND: Cognitive deficits have been recognized as a key feature of schizophrenia, since the first description by Kraepelin. Specifically, lower intelligence is considered a core feature of the disorder and may represent a risk factor for its development. However, whether global intelligence decreases over time in schizophrenia is not known. The aims of this quantitative meta-analysis are to gather, integrate and estimate the overall mean effect size of IQ change over time in schizophrenia as compared to healthy individuals. METHODS: A systematic search was conducted to identify relevant studies. Longitudinal studies with at least two intelligence assessments in schizophrenia cohorts were retrieved. Studies had to report sufficient data on IQ-change and include data from healthy comparisons for computation of effect sizes. For each study, the Cohen d was calculated as well as a combined mean effect size. RESULTS: Fourteen studies were identified. Eight studies with a total of 280 patients and 306 healthy controls were suitable to be included. The mean weighted baseline IQ was 97.20 for patients and 109.26 for controls. The mean weighted IQ-change per year was +0.33 for patients and +2.08 for controls. The combined effect size was Cohen's d = -0.48, p = 0.01. CONCLUSIONS: A global cognitive deficit is present in patients with schizophrenia expressed as a lower test score increase over repeated testing as compared to healthy subjects possibly due to the lack of practice effects in patients. Thus, schizophrenia is characterized by a relative lack of gain in global cognitive abilities over time.
BACKGROUND:Cognitive deficits have been recognized as a key feature of schizophrenia, since the first description by Kraepelin. Specifically, lower intelligence is considered a core feature of the disorder and may represent a risk factor for its development. However, whether global intelligence decreases over time in schizophrenia is not known. The aims of this quantitative meta-analysis are to gather, integrate and estimate the overall mean effect size of IQ change over time in schizophrenia as compared to healthy individuals. METHODS: A systematic search was conducted to identify relevant studies. Longitudinal studies with at least two intelligence assessments in schizophrenia cohorts were retrieved. Studies had to report sufficient data on IQ-change and include data from healthy comparisons for computation of effect sizes. For each study, the Cohen d was calculated as well as a combined mean effect size. RESULTS: Fourteen studies were identified. Eight studies with a total of 280 patients and 306 healthy controls were suitable to be included. The mean weighted baseline IQ was 97.20 for patients and 109.26 for controls. The mean weighted IQ-change per year was +0.33 for patients and +2.08 for controls. The combined effect size was Cohen's d = -0.48, p = 0.01. CONCLUSIONS: A global cognitive deficit is present in patients with schizophrenia expressed as a lower test score increase over repeated testing as compared to healthy subjects possibly due to the lack of practice effects in patients. Thus, schizophrenia is characterized by a relative lack of gain in global cognitive abilities over time.
Authors: Marc M Bohlken; Rachel M Brouwer; René C W Mandl; René S Kahn; Hilleke E Hulshoff Pol Journal: Schizophr Bull Date: 2016-04-07 Impact factor: 9.306
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Authors: James J Yi; Ronnie Weinberger; Tyler M Moore; Monica E Calkins; Yael Guri; Donna M McDonald-McGinn; Elaine H Zackai; Beverly S Emanuel; Raquel E Gur; Doron Gothelf; Ruben C Gur Journal: Brain Cogn Date: 2016-05-17 Impact factor: 2.310
Authors: Anne-Kathrin J Fett; Eva Velthorst; Abraham Reichenberg; Camilo J Ruggero; Jennifer L Callahan; Laura J Fochtmann; Gabrielle A Carlson; Greg Perlman; Evelyn J Bromet; Roman Kotov Journal: JAMA Psychiatry Date: 2020-04-01 Impact factor: 21.596
Authors: Jacob A S Vorstman; Elemi J Breetvelt; Sasja N Duijff; Stephan Eliez; Maude Schneider; Maria Jalbrzikowski; Marco Armando; Stefano Vicari; Vandana Shashi; Stephen R Hooper; Eva W C Chow; Wai Lun Alan Fung; Nancy J Butcher; Donald A Young; Donna M McDonald-McGinn; Annick Vogels; Therese van Amelsvoort; Doron Gothelf; Ronnie Weinberger; Abraham Weizman; Petra W J Klaassen; Sanne Koops; Wendy R Kates; Kevin M Antshel; Tony J Simon; Opal Y Ousley; Ann Swillen; Raquel E Gur; Carrie E Bearden; René S Kahn; Anne S Bassett Journal: JAMA Psychiatry Date: 2015-04 Impact factor: 21.596