Approaches to multiplicity in publicly funded pragmatic randomised controlled trials: a survey of clinical trials units and a rapid review of published trials

Table 5 Approach to multiplicity due to interim analyses

a) Review: approach taken to multiplicity
	Formal adjustment	Hierarchical testing	Other approach	None
Interim analyses	26/41^a (63%)	0/41 (0%)	2/41^b (5%)	13/41^c (32%)
b) Survey: responses to posed scenarios
	Always	Sometimes	Never	Unsure
Would you adjust for multiplicity if interim analysis(es) were pre-specified in the study protocol?	8/27 (30%)	12/27 (44%)	3/27 (11%)	4/27 (15%)

Notes: ^a Eight trials used the Haybittle-Peto procedure, eight used O’Brien-Fleming, seven partitioned the significance level between final and interim analyses (with no further details given), one used Pocock, one used Lan DeMets and one did not give details.
^bOne trial used a group sequential design and one used a conditional rejection probability approach.
^cOf these, three trials stated a pre-specified significance level for stopping the trial.

ISSN: 1471-2288