Background: Outcomes selected for systematic reviews (SRs) should address clinical uncertainties to help make treatment decisions. However, when reviewers select outcomes by specifying the outcome’s 5 elements (domain, measurement, method of aggregation, metric, and time point) these may not match outcomes reported in trials included in SRs.

Objectives: To examine from a selected Cochrane SR outcomes reported from eligible trials not meeting the review-outcome definition.

Methods: We selected a Cochrane SR comparing classes of medications given after cataract surgery, which had no trials contributing to meta-analyses of the primary outcome. Clinician authors of the SR defined the primary outcome as the proportion of participants with grade >1 on the Standardisation of Uveitis Nomenclature (SUN) scale at 1-week follow-up (dichotomous). The SUN scale ranges from 0-4 and indicates the amount of cells and flare in the anterior chamber of the eye; higher grades indicate worse inflammation. Cell and flare can be measured by a slit-lamp or a cell and flare meter, and are recorded as the number of cells, amount of flare, or a combination. We compared the number of studies providing inflammation data per the SR outcome definition with the number of studies providing inflammation data using other outcome definitions.

Results: Of 48 studies included in the SR, none reported dichotomous inflammation data. Eighteen studies reported inflammation as a continuous outcome; however, there was variation in outcome elements. Replacing the review outcomes with mean inflammation at 1-week follow-up, we were able to include data from 7 studies (n=484 participants) in meta-analysis. Extending follow-up to 1-month postoperatively would have added data from 4 more studies.

Conclusions: The choice to use a dichotomous rather than continuous outcome for inflammation scores resulted in a potential missed opportunity to use available data from trials. Additionally, dichotomization of continuous outcomes at arbitrary cut-points runs the risk of losing valuable information. Our results underscore the importance for core outcomes sets to address all 5 outcome elements.