Page 14 - Drug Class Review

Final Report Update 1 Drug Effectiveness Review Project

statistical analyses. We included recent pooled analyses of RCTs if they covered all published trials and
their methods were sound. We checked our database to ensure that our literature search had identified

trials included in any meta-analyses that we discarded; we then obtained any missing articles so that all
constituent studies would be represented in this review.

If we could not find sufficient evidence of efficacy or effectiveness from at least one randomized, double-
blinded, head-to-head trial, we reviewed placebo-controlled trials and randomized, controlled, open-label

trials. For comparing different drugs, however, the strength of evidence must be rated lower for these
results than for results from the preferred type of trial. Findings of placebo-controlled trials are hard to
compare across studies because disparate populations may respond differently.

Overall, we reviewed 1,167 article abstracts and retrieved 206 of those as full text articles for background

information or to be reviewed for inclusion into the evidence report.

C. Data abstraction

We designed and used a structured data abstraction form to ensure consistency in appraising each study.
Trained reviewers abstracted data from each study and assigned an initial quality rating; a senior reviewer

read each abstracted article, evaluated the completeness of the data abstraction, and confirmed the quality
rating. We abstracted the following data from included trials: study design, eligibility criteria,
intervention (drugs, dose, duration), additional medications allowed, methods of outcome assessment,

population characteristics, sample size, loss to follow-up, withdrawals attributed to adverse events,
results, and adverse events reported. We recorded intention-to-treat (ITT) results if available.

D. Quality assessment

We assessed the internal validity (quality) of trials based on predefined criteria (Appendix C). These
criteria are based on those developed by the US Preventive Services Task Force (ratings: good, fair, or
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poor) and the National Health Service Centre for Reviews and Dissemination. We assessed external
validity (generalizability) and reported on it, but these assessments did not influence our quality ratings.

Two independent reviewers assigned quality ratings; they resolved any disagreements by discussion and
consensus or by consulting a third independent party. Elements of internal validity assessment included,

among others, randomization and allocation concealment, similarity of compared groups at baseline, use
of ITT analysis, and overall and differential loss to follow-up.

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