TY - JOUR
T1 - IQ change over time in schizophrenia and healthy individuals
T2 - A meta-analysis
AU - Hedman, Anna M.
AU - van Haren, Neeltje E.M.
AU - van Baal, Caroline G.M.
AU - Kahn, René S.
AU - Hulshoff Pol, Hilleke E.
N1 - Funding Information:
This work was supported by NWO VIDI grant (grant no.: 917-46-370) (to H.H.) and European Twin Study Network on Schizophrenia grant (EUTwinsS); (grant no.: MRTN-CT-2006-035987).
PY - 2013/5
Y1 - 2013/5
N2 - 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.
AB - 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.
KW - IQ
KW - Longitudinal
KW - Meta-analysis
KW - Schizophrenia
UR - http://www.scopus.com/inward/record.url?scp=84875936861&partnerID=8YFLogxK
U2 - 10.1016/j.schres.2013.01.027
DO - 10.1016/j.schres.2013.01.027
M3 - Article
C2 - 23490758
AN - SCOPUS:84875936861
SN - 0920-9964
VL - 146
SP - 201
EP - 208
JO - Schizophrenia Research
JF - Schizophrenia Research
IS - 1-3
ER -