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Table 1 Summary of parameters used in the sample size calculation

From: 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

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