Skip to main content
. 2015 Dec 17;11:3111–3125. doi: 10.2147/NDT.S76700

Table 2.

Meta-analytic evidence of neurocognitive impairment in SZ listed in chronological order of publication

References Included studies and sample composition Affected cognitive domains in BD patient groups
46 204 studies comparing cognitive performance between SZ patients and community controls Overall mean impairment of 0.92 standard deviation in SZ patients as compared to controls, associated with medium-to-large ES deficits (−0.63<g<−1.11) across cognitive domains
65 29 studies comparing WCST performance between SZ patients and HC Large ES differences in category achieved (d=0.91), moderate ES differences in perseveration (d=0.53), and small ES differences in perseverative errors (d=0.18). Large ES differences for the Wechsler Adult Intelligence Scale IQ (d=1.23)
49 71 studies comparing the performance on the WCST/HCT, verbal/design fluency, Trail Making B (TMB), and the Stroop Color-Word Test between SZ patients and HC Large ES difference in both complex (ie, WCST/HCT) (delta=−1.42) and less complex (ie, TMB/Stroop) (delta=−1.58) measures of executive functions in SZ patients vs controls
55 13 studies comparing verbal fluency performance between SZ patients (n=526) and HC (n=389) Large ES differences in SZ patients vs controls, with greater deficits in semantic fluency (d=1.23) in comparison to letter fluency (d=1.01)
50 84 studies comparing recognition memory performance between SZ patients and HC Moderate ES difference (d=0.76) in overall recognition memory performance in SZ patients vs controls
66 84 studies comparing verbal fluency performance between SZ patients and HC Larger ES differences for semantic relative to phonemic fluency, reflecting a general intellectual impairment in SZ patients vs controls
47 37 studies comparing cognitive performance between SZ patients (n=1,961) and community controls (n=1,444) Overall mean impairment of 0.98 standard deviation in SZ patients as compared to controls, associated with large ES deficits in digit symbol coding (g=−1.57)
8 18 studies comparing IQ between individuals that later developed SZ and controls Moderate premorbid intellectual impairment (d=0.540) in future SZ cases vs controls
2 53 longitudinal studies evaluating cognitive performance in SZ patients (n=2,746) and in HC (n=324) with a median test–retest time of 4 months SZ patients exhibited mild improvements in learning and delayed recall tests (d=0.4), cognitive flexibility (d=0.38), and attention (d=0.35)
70 88 studies evaluating the correlations between executive functions and positive, negative symptoms and disorganization Small-to-moderate range correlations between both negative symptoms (r=−0.21) and disorganization (r=−0.17) with executive dysfunction, as well as with current IQ (r=−0.21) but not with positive symptoms
77 47 studies comparing cognitive performance between FES patients (n=2,204, mean age 25.5) and age and sex-matched HC (n=2,775) Medium-to-large impairment across 10 domains (0.64<d<1.2), being largest in immediate verbal memory and processing speed
73 Studies comparing cognitive performance between HC and SZ patients with youth-onset (23 studies), SZ patients with adult-onset (78 studies) or late-onset (after 60 years old) (nine studies) SZ patients with youth onset and adult-FES exhibited large ES deficits (d>0.8) in the majority of domains
SZ patients with youth onset had larger deficits as compared to patients with FES in IQ, executive functions, psychomotor speed, arithmetic, and verbal memory. SZ patients with late-onset had minimal deficits in arithmetic and vocabulary, but larger deficits in attention, fluency, IQ, and visuospatial construction
85 31 studies comparing cognitive performance between SZ patients (n=1,972) and individuals with affective psychosis or schizoaffective disorder (n=1,314) SZ patients underperformed individuals with affective psychosis on measures of verbal memory, working memory, IQ, TMT-B, and WCST with small between-group ES differences (0.25<d<0.42)
52 Eleven studies comparing prospective memory between SZ patients (n=485) and HC (n=409) Large ES impairment in time (d=−1.33), event (d=−0.83), and activity-based (d=−0.73) prospective memory in SZ patients vs controls
67 91 studies comparing performance in tests that measure semantic memory between SZ patients and HC Large ES impairment in naming and category fluency, medium ES impairment for word-picture matching and association tests, and small ES impairment for categorization and priming tests
51 187 studies (441 separate results) comparing working memory performance between SZ patients and HC Large ES differences across working memory domains in SZ patients vs controls
86 Studies comparing cognitive performance between patients with SZ and affective disorders Impairments in intellectual ability and speed of information processing, in encoding and retrieval, rule discovery and in response generation and response inhibition both in patients with SZ and affective disorders. In most cognitive domains participants with SZ had higher (and large) ES estimates
58 29 cross-sectional studies involving SZ patients aged >65 years and 14 longitudinal studies on cognitive performance (n=954 SZ patients followed up to 6 years) Cross-sectional analysis revealed large ES differences in global cognition (d=−1–19) and in measures of language (d=−1.30), immediate memory (d=−1.25) as well as executive functions (d=−1.14) Longitudinal analysis revealed small ES differences for measures of global cognition (d=−0–097)
56 47 studies comparing the performance on measures of processing speed between SZ patients (n=4,135) and HC (n=2,292) Largest ES differences in coding tasks (g=−1.50) and category fluency (g=−1–31)
87 12 studies comparing cognitive performance between individuals with early onset SZ (n=296, mean age 15.7) and subject with BD (n=374, mean age 13.6) and HC Individuals with early onset of SZ exhibited moderate to large ES differences as compared to HC in general cognitive abilities (g=−1.15), processing speed (g=−1.27) and motor skills (g=−0.58), while BD patients exhibited milder deficits, ranging from g=−0.42 for general cognitive abilities to g=−0.83 for verbal learning and memory
63 12 longitudinal population-based studies (4,396 cases and over 745,000 controls) evaluating premorbid IQ among individuals that later developed SZ Moderate decrements in premorbid IQ (ES-0.43) among future cases. Risk of SZ increased by 3.7% for every point decrease in IQ
68 36 studies comparing the performance on Stroop interference between SZ patients (n=1,081) and HC (n=1,026) Increased Stroop interference effect in response time (g=0.43) and accuracy (g=0.62) in SZ patients vs controls
53 240 studies comparing cognitive performance between SZ patients (n=10,120) and HC (n=7,929) Large ES differences in IQ (−0.96), memory functioning (−1.22), language (−0.99), executive functions (−1.10), and attention (−0.99)
64 23 prospective studies assessing cognitive and motor function in individuals aged <16 years who later developed SZ or a SZ spectrum disorder Moderate intellectual impairment (d=0.51) and deficits in motor function (d=0.56)
54 100 studies comparing cognitive performance between SZ patients (n=9,048) and HC (n=8,814) Impairment in all cognitive domains (grand mean ES difference Hedges’ g=−1.03), with largest impairment in processing speed (g=−1.25) and episodic memory (g=−1.23)
1 14 studies comparing intellectual abilities between SZ patients (n=280) and HC (n=306) IQ change per year was +0.33 for SZ patients vs 2.08 for controls, with medium-sized deficits for IQ change in patients vs controls
78 23 studies comparing cognitive performance between drug-naïve FES patients (n=1,106) and HC (n=1,885) Large ES differences in verbal memory (SMD=−1.03), processing speed (SMD=−1.03), and working memory (SMD=−0.97); medium ES differences in attention (SMD=−0.8), visual memory (SMD=−0.78), and executive functions (SMD=−0.74)

Note: See the text for meta-analyses of studies focusing on cognitive performance in individuals at FHR and CHR to psychosis.

Abbreviations: BD, bipolar disorder; CHR, clinical high risk; ES, effect size; FHR, familiar high risk; FES, first-episode schizophrenia; HC, healthy controls; HCT, Halstead Category Test; IQ, intelligence quotient; SMD, standardized mean difference; SZ, schizophrenia; TMT-B, trail making test B; WCST, Wisconsin Card Sorting Test.