Searching literature databases for health care economic evaluations: how systematic can we afford to be?

As the health care economic-evaluation literature continues to grow, a need for sound methods to conduct systematic reviews of the existing evidence is emerging. So far, reviews of economic evaluations have relied upon noncomprehensive sources and have adopted simplistic search methods, both likely to lead to biased results.

To provide evidence of the performance of alternative approaches for identifying published health care economic evaluations and to illustrate what forms of bias may affect systematic reviews of such studies.

The sensitivity and specificity of alternative search strategies were tested for the period January to March 1997, using seven major medical and social science literature databases, one economic evaluation database and a published bibliography. Studies were selected blindly by pairs of reviewers (agreement 94.1%-96.5%), using a two-stage procedure.

By limiting the scope of a review to Medline and by using appropriate search strategies, researchers may significantly reduce the number of nonrelevant references retrieved by their electronic searches (sensitivity 72%, specificity 75%, compared with more extensive strategies), which require exclusion by manual screening. The yield of searches based on specialized bibliographies and databases may be different because of variations in selection criteria, coverage and time lag for inclusion of references.

Medline is the key source for reviews of economic evaluations. Researchers may select from the search strategies proposed in this paper the one that offers an optimal balance between sensitivity and specificity in relation to the aims of their review. Manual searches and searches of databases other than Medline have a limited incremental yield. The sensitivity of all search strategies increases when tighter methodological standards are set, but more research is needed on methods for identifying methodologically sound studies.