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Re: Overstated cost effectiveness?

Dear Editor,

Huang and colleagues have prepared an estimate of the cost- effectiveness of the Victorian, Active Script Programme, which they conclude indicates a successful program and one suitable for wider adoption. Confidence in a cost effectiveness estimate depends on confidence in the evidence on effectiveness and costs.

The Active Script Program evaluation was designed to determine up- take of the program by GPs. For the crucial evidence on patient physical activity levels, the authors draw on the results of a different physical activity intervention reported in a non-peer reviewed, unpublished conference presentation by Bull (1999), which on inspection appears to indicate a just significant 20% difference in activity levels between control and intervention group at 6 months, which had fallen to a small (<5%) non significant difference in the percent active between intervention and control groups at 12 months. Huang and colleagues assume in the model a 20% increase in physical activity levels associated with Active Script, which is thus likely to be overstated, and is not varied in sensitivity analysis. Fifty percent of this group is presumed to maintain their activity levels long enough to accrue a health benefit, which is unreferenced, and not consistent with the data by Bull, which shows that by 12 months there has been 75% reduction in the difference observed at 6 months.

Another more intensive active script type intervention demonstrated an increase in the proportion of people physically active from baseline of <10% for the intervention group compared to control (Elley et al, 2002), which is considerably less than that assumed in the Huang et al (2004) evaluation.

The key effectiveness figure is likely to be overstated in the Huang et al (2004) model. We find the step taken in the economic analysis from GP awareness, knowledge and behaviour (which was measured) to patient behaviour (which was not rigorously measured) to be beyond the scope of the original data. It is likely that the estimates of cost effectiveness would be higher and less certain than those presented, and that it may have been more useful to highlight gaps in existing data.

References

(1). Bull F. Physical activity and General Practice: overview of the evidence. Prepared for the participants of Active Australia Symposium on Physical Activity in General Practice. Canberra, 1999.