A cluster-randomised, controlled trial to assess the impact of a workplace osteoporosis prevention intervention on the dietary and physical activity behaviours of working women: study protocol

Table 1 Summary of parameters used in the sample size calculation

Outcome measures and mediators	Effect size	ICC used in sample size calculation	Standard deviation used in sample size calculation	Design effect	Number of clusters	Total subjects to be recruited
						Before factoring in 30%attrition	After factoring in 30%attrition
Calcium intake (milligrams per day)	250 milligrams	0.5*	290 milligrams***	10.5	14.7	294	480
Physical activity duration (minutes per week)	60 minutes	0.05**	150 minutes****	1.95	13	255	420

*Calculated using standard deviation from National Nutrition Survey 1998 and based on conservative estimates of inter- and intra-cluster variance [23].
**Based on estimates from published studies [30, 31].
***Estimate from National Nutrition Survey 1998 [32].
****Based on estimates from published studies [33, 34].

ISSN: 1471-2458