Title

GRADE guidelines: 7. Rating the quality of evidence - Inconsistency

Date of this Version

12-1-2011

Document Type

Journal Article

Publication Details

Citation only

Guyatt, G. H., Oxman, A. D., Kunz, R., Woodcock, J., et al. (2011). GRADE guidelines: 7. Rating the quality of evidence - Inconsistency. Journal of clinical epidemiology, 64 (12), 1294-1302.

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2011 HERDC submission. FoR code: 111700

© Copyright Elsevier Inc., 2011. All rights reserved.

ISSN

0895-4356

Abstract

This article deals with inconsistency of relative (rather than absolute) treatment effects in binary/dichotomous outcomes. A body of evidence is not rated up in quality if studies yield consistent results, but may be rated down in quality if inconsistent. Criteria for evaluating consistency include similarity of point estimates, extent of overlap of confidence intervals, and statistical criteria including tests of heterogeneity and I2. To explore heterogeneity, systematic review authors should generate and test a small number of a priori hypotheses related to patients, interventions, outcomes, and methodology. When inconsistency is large and unexplained, rating down quality for inconsistency is appropriate, particularly if some studies suggest substantial benefit, and others no effect or harm (rather than only large vs. small effects). Apparent subgroup effects may be spurious. Credibility is increased if subgroup effects are based on a small number of a priori hypotheses with a specified direction; subgroup comparisons come from within rather than between studies; tests of interaction generate low P-values; and have a biological rationale.

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This document has been peer reviewed.