Reply

Abstract

The questions Dr. Lee raises are important. Traditionally, standard gambling and time trade-off measures are anchored by death as the worst condition and perfect health as the best condition, as Dr. Lee proposes in his letter. However, when investigators plan to study the adverse effects of a particular disease or status, they often use an alternative to perfect health for the upper anchor point; that is, a disease-free status, which in the field of ophthalmology is usually defined as perfect vision. Although using disease-free status instead of perfect health in cost-utility analyses seems to overestimate the cost-effectiveness of health interventions,1 the influence on the utility values is inconclusive in the literature.2–5 In Lee et al.’s study,2 although it used standard gambling to elicit the utility values, the anchor point of perfect vision underestimated the utility values compared with the anchor point of perfect health. However, in King et al.’s paper,3 the anchor point of perfect vision overestimated the utility values. For time trade-off methods, the effect of the upper anchor point on the utility values is also inconsistent.3–5 No significant difference between the 2 anchor points was reported.5 Moreover, the existing literature compares the effect of the 2 anchor points on the utility value of a certain disease status; however, few studies have reported the effect on the difference of the utility values between different states. The purpose of our current study was to analyze the effect of cataract surgery on the quality of life of the patients with coexisting vision-threatening diabetic retinopathy. The main outcomes measures were the changes in the utility values. Although the present anchor point might overestimate or underestimate the utility value of a certain disease state, the difference between the preoperative and postoperative states might counteract the effect of the anchor point, making the conclusion stable. In addition, we also recommend that future studies describe their anchor points clearly in the methodology and perhaps include both anchor points in the study design.6 In the field of ophthalmology, more studies have used the anchor point of perfect vision2; we used the same anchor point to make it easier to compare our results with those in studies of other ophthalmic diseases. Regarding Dr. Lee’s second question, we sought to make the description of our methodology concise to limit its length for publication purposes. Thus, we described the process of eliciting the utility values without giving a detailed description. During the study, we asked for the number of years to trade by repeatedly questioning until we were sure we reached the longest number of years the patient was actually willing to trade.