Participant recruitment and attrition in surgical randomised trials with placebo controls versus non-operative controls: a meta-epidemiological study and meta-analysis.

Median (IQR) attrition rates were lower in placebo trials (12.4% (6.1%–29.8%)) compared with non-operative control trials (20.7% (9.1%–33.3%)); however, these did not reach statistical significance.

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