Intra-cluster and inter-period correlation coefficients for cross-sectional cluster randomised controlled trials for type-2 diabetes in UK primary care

Table 7 Summary of systematic search of intra-cluster correlation coefficients (ICCs) used in previous trials

Trial author	Outcome used	ICC used	Standard deviation used	ICC reported
Bellary et al. [47]	HbA1c	0.05	2.1
Dallosso et al. [50]	HbA1c	0.05	1.5
Khunti et al. [14]	HbA1c	0.05	2.0	0.02 (0.00–0.08)
Mathers et al. [49]	HbA1c	0.047	1.5
Smith et al. [39]	HbA1c	0.001	1.6
Smith et al. [51]	HbA1c	0.047	1.5
Sturt et al. [48]	HbA1c	0.047		0.0253
Bebb et al. [38]	BP	0.02	Binary outcome	0.035
Bellary et al. [47]	SBP	0.035	21.25
Smith et al. [39]	SBP	0.001	Binary outcome
Bellary et al. [47]	Cholesterol	0.05	1.1
Smith et al. [39]	Cholesterol	0.06	Binary outcome

Here glycosylated haemoglobin (HbA1c) represents a difference in average HbA1c levels between patients in the control and intervention groups. SBP represents systolic blood pressure, BP represents blood pressure – where a reading of both systolic and diastolic blood pressure was taken, and cholesterol represents total cholesterol level

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