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

Table 4 Approach to multiplicity due to subgroup analyses

a) Review: multiplicity approach taken
	Formal adjustment	Hierarchical testing	Other approach	None
Subgroup analyses	8/85^a (9%)	0/85 (0%)	0/85 (0%)	77/85^b (91%)
b) Survey: responses to posed scenarios
		Yes	No	Unsure
Would you consider adjusting for multiplicity arising from performing multiple subgroup analyses?		6/27 (22%)	17/27 (63%)	4/27 (15%)
Consider a parallel group trial with multiple subgroup analyses performed. Would you adjust for multiplicity in the following scenarios?
Subgroup analyses pre-specified in the study protocol?		3/27 (11%)	22/27 (81%)	2/27 (7%)
Subgroup analyses determined post-hoc?		4/27 (15%)	22/27 (81%)	1/27 (4%)
Subgroup analyses specified for the following reasons: a) to confirm biological plausibility, b) to confirm existing hypotheses, AND c) to show subgroup effects for supporting decision making in target populations.		3/27 (11%)	19/27 (70%)	5/27 (19%)
Would you be more likely to adjust for multiplicity if the number of subgroup analyses was increased?		5/27 (19%)	21/27 (78%)	1/27 (4%)

Notes: ^a One trial performed a Bonferroni correction, two a Holm correction and five studies used a threshold of 1% for significance
^b Of these, five studies stated that results from secondary outcomes were exploratory/hypothesis generating

ISSN: 1471-2288