EuroQol values for economic modeling quality of life after infrainguinal bypass grafting surgery: a rectification

Abstract

In the May edition of the Journal of Vascular Surgery , the outcomes of our investigation into the quality of life after infrainguinal bypass grafting surgery were published.1Tangelder MJD McDonnel J Busschbach JJV Buskens E Algra A Lawson JA et al.Quality of life after infrainguinal bypass grafting surgery.J Vasc Surg. 1999; 29: 913-919Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar Unfortunately, the graph that accompanied the article only contained the EuroQol values for the female patients. Fortunately, the error did not jeopardize the main interpretation of the results because we found no evidence of interaction between gender and group variables. We were interested in differences between groups, and these differences were not influenced by the (constant) differences between sex. Because all the results were interpreted as relative values between patient groups, the constant differences between men and women did not play a role in the formulation of the conclusion. Nevertheless, in the judging of the absolute values of quality of life, the graph suggested a lower average quality of life than was actually measured because women, in general, valued their quality of life lower than men. In other words, the values that were presented in the graph underestimated the average quality of life. This error ranged from 4 to 10 points on a scale from 0 to 100. Although the low values in the graph did not affect the interpretation of the results of this particular investigation, the values may lead to erroneous conclusions when they are judged as absolute values. In particular, this situation may arise when these values are used in cost-effectiveness analyses and in the economic modeling of outcomes. In a cost-effectiveness analysis, the outcomes of an intervention are compared with other health care interventions. Obviously, if the low values that were presented in the original graph are used, then the conclusions of such comparisons may be erroneous. This observation applies particularly to the EuroQol data because these values are often used in economic evaluation and modeling. For this reason, we present the EuroQol values for both men and women in Table I. Table IQuality of life after infrainguinal bypass grafting on the basis of the EuroQol questionnaireWomenMenMean score95% CIMean score95% CIEQ-5Dindex Patent graft0.630.59 - 0.660.710.67 - 0.74 Asymptomatic occlusion0.590.50 - 0.680.670.58 - 0.76 Symptomatic occlusion0.520.45 - 0.580.600.53 - 0.66 Revascularization0.530.49 - 0.570.610.57 - 0.65 Primary amputation0.430.33 - 0.530.510.41 - 0.61 Secondary amputation0.330.24 - 0.430.410.32 - 0.51 Cerebrovascular accident0.400.29 - 0.510.480.37 - 0.59 Myocardial infarction0.510.37 - 0.650.590.45 - 0.73EQVAS Patent graft64.4962.08 - 66.9070.0067.59 - 72.41 Asymptomatic occlusion64.9059.12 - 70.6870.4164.63 - 76.19 Symptomatic occlusion57.6253.35 - 61.8963.1358.86 - 67.40 Revascularization61.0658.29 - 63.8366.5763.80 - 69.34 Primary amputation59.7253.37 - 66.0765.2358.88 - 71.58 Secondary amputation55.0948.99 - 61.1960.6054.50 - 66.70 Cerebrovascular accident49.4441.83 - 57.0554.9547.34 - 62.56 Myocardial infarction52.4643.00 - 61.9257.9748.51 - 67.43CI, Confidence interval. Open table in a new tab CI, Confidence interval. Table I presents two different EuroQol scores on the basis of a multilevel analysis.1Tangelder MJD McDonnel J Busschbach JJV Buskens E Algra A Lawson JA et al.Quality of life after infrainguinal bypass grafting surgery.J Vasc Surg. 1999; 29: 913-919Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar The EQ VAS is the value that patients attribute to their own current health state with the placement of a mark on a visual analogue scale, labeled from 0 (worst imaginable health state) to 100 (best imaginable health state). These values represent the patient’s perspective. The EQ-5Dindex is a weighted aggregated score for the five EuroQol dimensions of quality of life. This index score is based on the values of the general public and therefore represents the societal perspective, which is the preferred perspective in the economic evaluation of health care. In this case, the weighing was on the basis of responses from a sample of 3000 households in the United Kingdom.2Dolan P. Modeling valuations for the EuroQol health states.Med Care. 1997; 35: 1095-1108Crossref PubMed Scopus (3193) Google Scholar This EQ-5Dindex has a range from –1.00 to 1.00, in which the value 1.00 represents health without morbidity, 0.00 represents morbidity with the same value as death, and –1.00 is the lowest value for health states with values lower than death. These values are based on time trade-off, which makes them especially suitable for the analysis of quality-adjusted life years. When the EuroQol values are used in a model, the values should be weighed for the proportion of male and female patients. 24/41/102588