Clinical trials make up a much larger body of literature than do randomized trials. Also, authors have a bewildering number of ways of referring to clinical trials, making searching for them a particular challenge. If you wish to included non-randomized trials in your review or analysis, it is best not to limit. If you must, clinical trials will be retrieved as part of the PubMed Clinical Queries sensitive search:
("clinical"[tiab] AND "trial"[tiab]) OR "clinical trials as topic"[mesh] OR "clinical trial"[pt] OR random*[tiab] OR "random allocation"[mesh] OR "therapeutic use"[sh]
A broader strategy, modified slightly from [1], can be used:
"randomized controlled trial"[pt] OR "controlled clinical trial"[pt] OR "clinical trials as topic"[mesh] OR "random allocation"[mesh] OR "double-blind method"[mesh] OR "single-blind method"[mesh] OR "clinical trial"[pt] OR "research design"[mesh:noexp] OR "comparative study"[pt] OR "evaluation studies"[pt] OR "follow-up studies"[mesh] OR "prospective studies"[mesh] OR "cross-over studies"[mesh] OR "clinical trial"[tw] OR ((singl*[tw] OR doubl*[tw] OR trebl*[tw]) AND (mask*[tw] OR blind*[tw])) OR placebo*[tw] OR random*[tw] OR "control"[tw] OR "controls"[tw] OR prospectiv*[tw] OR volunteer*[tw]
This strategy was reported to have greater than 99% sensitivity on a small test set. The precision was not reported, though it must be about 13%, which is approximate precision of the Clinical Queries hedge.
Further Reading:
1. Robinson KA, Dickersin K. Development of a highly sensitive search strategy for the retrieval of reports of controlled trials using PubMed. Int J Epidemiol. 2002 Feb;31(1):150-3. PubMed PMID: 11914311.
