Length of time periods in treatment effect descriptions and willingness to initiate preventive therapy : a randomised survey experiment
Background Common measures used to describe preventive treatment effects today are proportional, i.e. they compare the proportions of events in relative or absolute terms, however they are not easily interpreted from the patient's perspective and different magnitudes do not seem to clearly discriminate between levels of effect presented to people. Methods In this randomised cross-sectional survey experiment, performed in a Swedish population-based sample (n=1041, response rate 58.6%), the respondents, aged between 40 and 75years were given information on a hypothetical preventive cardiovascular treatment. Respondents were randomised into groups in which the treatment was described as having the effect of delaying a heart attack for different periods of time (Delay of Event,DoE): 1month, 6months or 18months. Respondents were thereafter asked about their willingness to initiate such therapy, as well as questions about how they valued the proposed therapy. ResultsLonger DoE:s were associated with comparatively greater willingness to initiate treatment. The proportions accepting treatment were 81, 71 and 46% when postponement was 18months, 6months and 1month respectively. In adjusted binary logistic regression models the odds ratio for being willing to take therapy was 4.45 (95% CI 2.72-7.30) for a DoE of 6months, and 6.08 (95% CI 3.61-10.23) for a DoE of 18months compared with a DoE of 1month. Greater belief in the necessity of medical treatment increased the odds of being willing to initiate therapy. ConclusionsLay people's willingness to initiate preventive therapy was sensitive to the magnitude of the effect presented as DoE. The results indicate that DoE is a comprehensible effect measure, of potential value in shared clinical decision-making.