Sample size determination for external pilot cluster randomised trials with binary feasibility outcomes: a tutorial

Hemming, K.; Taljaard, M.; Gkini, E.; Bishop, J.

doi:10.1186/s40814-023-01384-1

Pilot and Feasibility Studies

Table 2 Estimates of intra-cluster correlation coefficients for feasibility outcomes from a convenience sample of trials

From: Sample size determination for external pilot cluster randomised trials with binary feasibility outcomes: a tutorial

Trial	Feasibility outcome description	Design	Setting	No. of clusters	TSS	Proportion	ICC	SE	LCI	UCI
KG SEAR	Agree to be randomised out of those eligible	RCT	Secondary care UK	19	760	0.34	0.08	0.04	0.03	0.20
INTERVAL	Availability of primary outcome: bleeding gums	RCT	Dentistry UK	51	2374	0.68	0.09	0.02	0.05	0.14
	Availability of secondary outcome: patient-reported outcome	RCT	Dentistry UK	51	2374	0.72	0.11	0.03	0.07	0.18
IQuaD	Availability of primary outcome: bleeding gums	CRT	Dentistry UK	63	2021	0.66	0.07	0.02	0.04	0.12
	Availability of secondary outcome: patient self-efficacy	CRT	Dentistry UK	63	2021	0.72	0.05	0.01	0.03	0.09
VUE	Availability of outcome: patient-reported prolapse symptoms (POP-SS)	RCT	Women’s Health UK	46	781	0.82	0.01	0.01	0.00	0.15
	Availability of outcome: quality of life^a	RCT	Women’s Health UK	46	781	0.83	0.00	0.01	0.00	0.03
Trigger	Adherence to transfusion policy	CRT	UK Transplant	6	935	0.70	0.12	0.07	0.04	0.33
	Received at least 1 RBC transfusion	CRT	UK Transplant	6	935	0.41	0.04	0.03	0.01	0.16
Will	Availability of primary outcome 1: severe composite maternal morbidity	RCT	Maternity care UK	45	403	0.96	0.14	0.06	0.06	0.28
	Availability of co-primary outcome: neonatal NICU admission	RCT	Maternity care UK	45	403	0.96	0.23	0.07	0.12	0.39
ROCSS	Availability of primary outcome: hernia within 2 years	RCT	Surgery Europe	37	390	0.82	0.03	0.02	0.01	0.11
ABA-feed	Availability of primary outcome which is breastfeeding at 8 weeks^a	RCT	Maternity care UK	102	357	0.92	0.00	0.05	0.00	0.9
APPEAL 2	Questionnaire return	CRT (pilot)	Maternity care UK	17	997	0.18	0.04	0.02	0.01	0.11
GBS2	Receipt of antibiotics	CRT	Maternity care UK	20	1622	0.39	0.06	0.02	0.03	0.13
WAVES	BMI availability (baseline)	CRT	Schools UK	54	1467	0.95	0.01	0.01	0.00	0.08
	BMI availability (first follow-up)	CRT	Schools UK	54	1467	0.85	0.12	0.03	0.07	0.19
	BMI availability (second follow-up)	CRT	Schools UK	54	1467	0.78	0.08	0.02	0.04	0.13
						Median	0.07	0.02	0.03	0.14
						UQR	0.11	0.04	0.05	0.18

TSS total sample size, no. of clusters number of clusters/centres, SE standard error (of ICC), ICC intra-cluster correlation coefficient for the feasibility outcome, LCI lower 95% confidence interval, UCI upper 95% confidence interval, UQR upper quartile
^aUse loneway and reported ICC truncated at zero. Information on trial sources is available in the supplementary material B

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ISSN: 2055-5784

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