The effectiveness and cost-effectiveness of the Green Prescription physical activity intervention: a cluster randomised controlled trial in primary health care

Abstract

This thesis assesses the effectiveness and cost-effectiveness of the 'Green Prescription' physical activity intervention amongst less-active adults in primary care, using the Auckland Heart Study (AHS) questionnaire to assess change in activity. The validity of two physical-activity questionnaires, the AHS and the GSS questionnaires, was assessed initially, comparing their performance with 7-day activity diaries and pedometers amongst less-active adults in primary care. A cluster randomised controlled trial was then conducted in the waikato region of New Zealand, with 42 general practices randomised to give the Green Prescription or 'usual care'. A systematic screening process identified less-active 40-79 year-old patients. Main outcome measures included change in physical activity, quality of life (SF-36), coronary risk, and blood pressure, over a twelve-month period. Costs of the programme and offset costs of primary and secondary health care utilisation, productivity, and exercising, were collected prospectively for cost-effectiveness analysis from a societal perspective. The AHS questionnaire was found to have adequate reliability and validity, and to be the most appropriate measurement tool for use in primary care research. In the Green Prescription trial, 74% of general practitioners (n=117) and 66% of screened eligible patients (n=878) participated. Follow-up rate, at one year, was 85% (n=750). Mean total energy expenditure increased by 9.4 kcal/kg/week (p=0.001) and leisure exercise by 2.7.kcal/kg/week (p=0.02) or 34 minutes/week more in the intervention group than the control group (p=0.04). The proportion of the intervention group undertaking 21/2 hours/week of leisure exercise increased by 9.72% (p=0.003) more than in the control group (NNT=10.3). SF-36 measures of 'general health', 'role-physical', 'vitality', and ‘bodily pain' improved significantly more in the intervention group (p<0.05), as a result of the Green Prescription intervention. There was a trend towards decreasing blood Pressure, no increase in adverse events, and no statistically significant difference in four-year risk of coronary heart disease. The cost of delivering the Green prescription was $170.45 per participant from a funder's perspective and $37.16 (95%CI:-$945.21,$1019.53) from a societal perspective. To increase leisure-time exercise by one hour per week cost $25.36 per month from a programme funder's perspective and $5.47 (95%CI:-$138.90,$149.84)per month from a societal perspective. The AHS questionnaire was considered reliable and valid. The Green Prescription intervention is effective in increasing physical activity and improving quality of life over 12 months without evidence of adverse effects. The intervention is more cost-effective than other physical activity interventions reported in the literature and may be cost-saving in terms of long-term health gains.