This Article  • Full text  • PDF  • Reply to article  • Send to a friend  • Save in My Folder  • Save to citation manager  • Permissions  Citing Articles  • Citation map  • Citing articles on HighWire  • Citing articles on ISI (11)  • Contact me when this article is cited  Related Content  • Similar articles in this journal  Topic Collections  • Neurology  • Cognitive Disorders  • Schizophrenia  • Evidence-Based Medicine  • Alert me on articles by topic

A Meta-analytic Comparison of Digit Symbol Coding Tasks and Other Cognitive Measures in Schizophrenia

Dwight Dickinson, PhD; Mary E. Ramsey, BS; James M. Gold, PhD

Arch Gen Psychiatry. 2007;64(5):532-542.

Context  In focusing on potentially localizable cognitive impairments, the schizophrenia meta-analytic literature has overlooked the largest single impairment: on digit symbol coding tasks.

Objective  To compare the magnitude of the schizophrenia impairment on coding tasks with impairments on other traditional neuropsychological instruments.

Data Sources  MEDLINE and PsycINFO electronic databases and reference lists from identified articles.

Study Selection  English-language studies from 1990 to present, comparing performance of patients with schizophrenia and healthy controls on coding tasks and cognitive measures representing at least 2 other cognitive domains. Of 182 studies identified, 40 met all criteria for inclusion in the meta-analysis.

Data Extraction  Means, standard deviations, and sample sizes were extracted for digit symbol coding and 36 other cognitive variables. In addition, we recorded potential clinical moderator variables, including chronicity/severity, medication status, age, and education, and potential study design moderators, including coding task variant, matching, and study publication date.

Data Synthesis  Main analyses synthesized data from 37 studies comprising 1961 patients with schizophrenia and 1444 comparison subjects. Combination of mean effect sizes across studies by means of a random effects model yielded a weighted mean effect for digit symbol coding of g = –1.57 (95% confidence interval, –1.66 to –1.48). This effect compared with a grand mean effect of g = –0.98 and was significantly larger than effects for widely used measures of episodic memory, executive functioning, and working memory. Moderator variable analyses indicated that clinical and study design differences between studies had little effect on the coding task effect. Comparison with previous meta-analyses suggested that current results were representative of the broader literature. Subsidiary analysis of data from relatives of patients with schizophrenia also suggested prominent coding task impairments in this group.

Conclusion  The 5-minute digit symbol coding task, reliable and easy to administer, taps an information processing inefficiency that is a central feature of the cognitive deficit in schizophrenia and deserves systematic investigation.

Author Affiliations: VISN 5 Mental Illness Research, Education and Clinical Center (Drs Dickinson and Gold), Department of Psychiatry, University of Maryland School of Medicine (Drs Dickinson and Gold), and Maryland Psychiatric Research Center, Baltimore (Ms Ramsey and Dr Gold), Baltimore.

THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES

Digit symbol coding and general cognitive ability in schizophrenia: worth another look?
Dickinson
Br. J. Psychiatry 2008;193:354-356.
ABSTRACT | FULL TEXT  

Neurocognitive Decline in Early-Onset Schizophrenia Compared With ADHD and Normal Controls: Evidence From a 13-Year Follow-up Study
Oie et al.
Schizophr Bull 2008;0:sbn127v1-sbn127.
ABSTRACT | FULL TEXT  

Systemic Hypotheses for Generalized Cognitive Deficits in Schizophrenia: A New Take on An Old Problem
Dickinson and Harvey
Schizophr Bull 2008;0:sbn097v1-sbn097.
ABSTRACT | FULL TEXT  

The Relationship Between IQ, Memory, Executive Function, and Processing Speed in Recent-Onset Psychosis: 1-Year Stability and Clinical Outcome
Leeson et al.
Schizophr Bull 2008;0:sbn100v1-sbn100.
ABSTRACT | FULL TEXT  

Cognitive Performance and Functional Competence as Predictors of Community Independence in Schizophrenia
Heinrichs et al.
Schizophr Bull 2008;0:sbn095v1-sbn095.
ABSTRACT | FULL TEXT  

Implementation Considerations for Multisite Clinical Trials with Cognitive Neuroscience Tasks
Keefe and Harvey
Schizophr Bull 2008;34:656-663.
ABSTRACT | FULL TEXT  

Evidence of Exacerbated Cognitive Deficits in Schizophrenia Patients With Comorbid Diabetes
Dickinson et al.
Psychosomatics 2008;49:123-131.
ABSTRACT | FULL TEXT  

Galantamine for the Treatment of Cognitive Impairments in People With Schizophrenia
Buchanan et al.
Am. J. Psychiatry 2008;165:82-89.
ABSTRACT | FULL TEXT  

Cognitive Neuroscience-Based Approaches to Measuring and Improving Treatment Effects on Cognition in Schizophrenia: The CNTRICS Initiative
Carter and Barch
Schizophr Bull 2007;33:1131-1137.
ABSTRACT | FULL TEXT