The original data source for the benefit of statins is an HTA monograph: A systematic review and economic evaluation of statins for the prevention of coronary events. S Ward, M Lloyd Jones, A Pandor, M Holmes, R Ara, A Ryan, W Yeo and N Payne. Health Technology Assessment 2007; Vol. 11: No. 14. It can be found at www.ncchta.org/fullmono/mon1114.pdf.
This monograph informed the recent NICE guidelines on lipid modification. I have used the primary prevention analysis from Figure 13 on page 34. This shows the benefit of Simvastatin in primary prevention from the HPS study subgroup in terms of the impact of treatment on CHD death, non-fatal MI, total stroke and coronary revascularisations. For convenience the Relative Risk of 0.77 with its confidence interval of 0.70 to 0.85 has been adopted (with a rounding down of the Relative Risk to 0.75 to match the figures used by the National Prescribing Centre).
There are many assumptions in the use of this data with a 10 year CVD risk. In the trials the baseline risk is much lower than 20% and we have to assume that the Relative Risk is both stable over time and different baseline risks. These assumptions are not currently tested, but the magnitude of benefit in secondary prevention trials (which have much higher baseline risks) is of the same order as the Relative Risk used above.
The calculations should therefore be regarded as being a rough guide for illustrative purposes, particularly as the benefit of treatment for any one individual will always be unknown. Visual Rx can only demonstrate what we expect to happen to 100 patients with a specified baseline risk if are all given statins over a 10 year period.