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English language studies were identified by searching Medline (1966–2001) and the Cochrane Library, and by reviewing bibliographies of retrieved articles.
Studies were selected if they were randomised controlled trials (RCTs) or observational cohort controlled trials.
Data were extracted on study design, intervention, and outcomes.
34 studies met the selection criteria. Meta-analysis was not done because of study variations in the diagnostic …
Sources of funding: Department of Veterans Affairs and National Institutes of Health.
For correspondence: Dr H R Collard, Division of Pulmonary Sciences and Critical Care Medicine, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO, USA.