PMD16 Implication of Preventing Disease on Life Years Gained (LYG)

While prevention of disease may lead to increased survival, appropriate estimation of LYG from shorter-term clinical trials has been controversial, with some arguing that only the gain actually observed during the trial is correct. The disagreement arises from a misunderstanding of the methods used. OBJECTIVE: To examine this misunderstanding using the estimation of LYG by preventing cardiovascular disease (CVD) with pravastatin in hypercholesterolemic subjects without pre-existing disease, based on the West of Scotland Coronary Prevention Study. METHODS: In WOSCOPS, there were 29 additional survivors among treated patients accumulating 71.05 years during the trial. But what happens at the end of the trial? Should one assume they all die immediately? A more reasonable presumption is that they attain their age and gender appropriate life expectancy. Although hypercholesterolemic, they have been successfully treated, and other trial selection criteria imply that they tend to be healthier than their peers. A more difficult issue concerns the non-fatal events prevented. Assigning no gain in life expectancy to the 76 additional survivors in the pravastatin group who remained free of cardiovascular disease (CVD) is tantamount to dismissing the impact of CVD on survival—a clinically untenable position. Instead, we estimated it using data from the Scottish Record Linkage System on 460,000 residents who had suffered a first CVD. CONCLUSION: As LYG has become the predominant denominator in cost-effectiveness ratios, their proper estimation is crucial. Over- or under-estimation can lead to erroneous conclusions by decision makers about the economic efficiency of therapeutic interventions.