Design of the Month

Incentives for physical activity

The following quotation is taken from a report by Andrew Garratt in the December 2007 issue of RSS News. It refers to the 2007 Beveridge lecture, which was given by Julian Le Grand.

As an example, he noted a study of the effectiveness of three alternative combinations of methods to promote physical activity in Newcastle. In this, 523 adults were randomised to one control group and four intervention groups that consisted of either a brief (one interview) or intensive (six interviews over 12 weeks) motivational interviewing, with or without financial incentives (30 vouchers entitling free access to leisure facilities). `The most effective intervention was the one involving six motivational interviews and a financial incentive: 55 percent of these participants had increased physical activity scores, compared with 35 per cent in the group that only received intense motivational interviewing'.

  1. What were the observational units and how many of them were there?
  2. What were the experimental units?
  3. What were the treatments and how many of them were there?
  4. Draw the Hasse diagram for the factors on the treatments.
  5. Draw the Hasse diagram showing all models defined by these treatment factors.

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