Table 2.

Estimates of sample size for primary and secondary outcomes

Outcome	Intra-cluster correlation coefficient	Design effect (30 patients per practice)	Effect size/different proportions	Sample size estimate for each group
Advice on diet	0.051	2.48	25%	170
Advice on physical activity	0.035	2.02	25%	140
Referral/attendance diet	0.026	1.75	25%	115
Referral/attendance physical activity	0.011	1.32	25%	80
Mean health literacy score	0.014	1.41	0.4	140
Mean diet score	0.001	1.03	0.4	115
Mean physical activity score	0.018	1.52	0.4	150
Mean BMI	0.038	2.10	0.5	135