Sampling methods IIIBMJ 2011; 342 doi: http://dx.doi.org/10.1136/bmj.d1537 (Published 17 March 2011) Cite this as: BMJ 2011;342:d1537
- Philip Sedgwick, senior lecturer in medical statistics
A randomised controlled trial investigated whether physical activity in preschool children (under 5 years) reduced obesity. The active intervention was an enhanced physical activity programme plus health education, whereas the control treatment was no intervention. All preschool nurseries in Glasgow were invited to participate.1
Each nursery was categorised by three characteristics thought to affect the intervention and the study outcomes. These characteristics were type of nursery (school, class, extended day, private sector), size of nursery (area and number of children), and socioeconomic status of the area. For each set of preschool nurseries with the same characteristics, two were randomly selected from those that agreed to participate, one of which was randomly allocated to active intervention and the other to control. In total, the trial investigated 36 preschool nurseries. …
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