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. 2014 Oct 16;9(10):e109400.
doi: 10.1371/journal.pone.0109400. eCollection 2014.

Outcomes in Cochrane systematic reviews addressing four common eye conditions: an evaluation of completeness and comparability

Ian J Saldanha  1 , Kay Dickersin  1 , Xue Wang  1 , Tianjing Li  1
Affiliations

Outcomes in Cochrane systematic reviews addressing four common eye conditions: an evaluation of completeness and comparability

Ian J Saldanha et al. PLoS One. .

Abstract

Introduction: Choice of outcomes is critical for clinical trialists and systematic reviewers. It is currently unclear how systematic reviewers choose and pre-specify outcomes for systematic reviews. Our objective was to assess the completeness of pre-specification and comparability of outcomes in all Cochrane reviews addressing four common eye conditions.

Methods: We examined protocols for all Cochrane reviews as of June 2013 that addressed glaucoma, cataract, age-related macular degeneration (AMD), and diabetic retinopathy (DR). We assessed completeness and comparability for each outcome that was named in ≥ 25% of protocols on those topics. We defined a completely-specified outcome as including information about five elements: domain, specific measurement, specific metric, method of aggregation, and time-points. For each domain, we assessed comparability in how individual elements were specified across protocols.

Results: We identified 57 protocols addressing glaucoma (22), cataract (16), AMD (15), and DR (4). We assessed completeness and comparability for five outcome domains: quality-of-life, visual acuity, intraocular pressure, disease progression, and contrast sensitivity. Overall, these five outcome domains appeared 145 times (instances). Only 15/145 instances (10.3%) were completely specified (all five elements) (median = three elements per outcome). Primary outcomes were more completely specified than non-primary (median = four versus two elements). Quality-of-life was least completely specified (median = one element). Due to largely incomplete outcome pre-specification, conclusive assessment of comparability in outcome usage across the various protocols per condition was not possible.

Discussion: Outcome pre-specification was largely incomplete; we encourage systematic reviewers to consider all five elements. This will indicate the importance of complete specification to clinical trialists, on whose work systematic reviewers depend, and will indirectly encourage comparable outcome choice to reviewers undertaking related research questions. Complete pre-specification could improve efficiency and reduce bias in data abstraction and analysis during a systematic review. Ultimately, more completely specified and comparable outcomes could make systematic reviews more useful to decision-makers.

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Conflict of interest statement

Competing Interests: All authors are affiliated with the US Satellite of the Cochrane Eyes and Vision Group (the group responsible for producing the Cochrane Reviews evaluated as part of this work): Drs. Kay Dickersin and Tianjing Li are Faculty members; Dr. Xue Wang is a Methodologist; and Dr. Ian Saldanha is a Research Assistant. Drs. Kay Dickersin, Tianjing Li, and Xue Wang have authored several Cochrane systematic reviews that are assessed as part of this study. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Figures

Figure 1
Figure 1. Examples of extent of overlap of possible outcome domains chosen by clinical trialists and systematic reviewers.
Yellow - Outcomes chosen by clinical trialists. Blue - Outcomes chosen by systematic reviewers. Grey - Outcomes chosen by BOTH clinical trialists and systematic reviewers.
Figure 2
Figure 2. Five elements of a completely specified outcome, with anxiety as an example.
Figure 3
Figure 3. Completeness of specification of outcome elements, by outcome.
Navy blue - Domain. Orange – Specific measurement. Yellow – Specific metric. Green – Method of aggregation. Blue – Time-point(s).
Figure 4
Figure 4. Completeness of specification of outcome elements, by condition.
Navy blue - Domain. Orange – Specific measurement. Yellow – Specific metric. Green – Method of aggregation. Sky blue – Time-point(s).
See this image and copyright information in PMC

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