TO THE EDITOR

The authors of the manuscript entitled "The psychometric properties of four quality of life instruments used in cardiovascular populations" have made an admirable effort to review the literature on the psychometric properties of four health-related quality of life (HRQL) questionnaires. 1 As the developers of the Quality of Life after Myocardial Infarction (QLMI) and the modified version, the MacNew Heart Disease Health-related Quality of Life questionnaire, we would like to point out limitations of the authors' discussion of the MacNew.

We originally developed and tested the QLMI in a randomized controlled trial of cardiac rehabilitation in patients surviving an acute myocardial infarction. 2,3 Lim and colleagues later modified the QLMI to be self-administered and tested the modified instrument. 4 Its current name, MacNew, acknowledges the roles of researchers at McMaster University, Ontario, Canada and the University of Newcastle, New South Wales, Australia.

DeVon and Ferrans define the psychometric properties of interest in this review as validity, reliability, and responsiveness. 1 DeVon and Ferrans suggest that correlations with the six measures in the original validation study by Hillers and colleagues were too low to support the validity of the QLMI. To support validity, they suggest that correlations should be as high as 0.70 to 0.75. However, they do not use this criterion consistently across instruments-indeed, only 4/30 of the correlations they report for the other three instruments they reviewed, the SF-36, the Seattle Angina Questionnaire, and their own Quality of Life Index, Cardiac Version III, meet this criterion. The authors also neglect to point out that the Hillers validation study of the MacNew used the strongest validation methodology available, the use of a priori predictions of how the instrument should behave if it were really measuring the intended constructs. We deliberately chose a wide variety of measures to compare to the QLMI, 3 anticipating weak (eg, QLMI physical restrictions and Beck depression), moderate (eg, QLMI emotions and Beck depression), or strong correlations (eg, QLMI symptoms and exercise tolerance) between the QLMI and specific instruments; although, when no criterion standard is available, correlations greater than 0.5 are seldom observed and not expected. The results were consistent with our predictions and, together with substantial correlations between the QLMI and the other emotional function measures (eg, QLMI emotions and POMS depression, QLMI confidence and state anxiety, QLMI self-esteem and Beck depression), we interpret these data as providing strong support for the instrument's discriminative validity and moderate support for evaluative validity.

Support for the validity and reliability of the MacNew, the modified QLMI, come from six published studies that DeVon and Ferrans have ignored. 5-10 There is one more recently published study 11 and four manuscripts in press or submitted about which DeVon and Ferrans could not have known without direct contact with the authors. The original MacNew factor analysis by Lim and colleagues 4 is substantiated in the English 5 and Spanish MacNew, 7 in three submitted manuscripts on the Dutch, German, and Farsi translations of the MacNew in patients with myocardial infarction, and in a more recently published manuscript on the German MacNew in patients with angina. 11 The correlations between the MacNew physical and emotional domains and the SF-36 physical and mental component scales of the SF-36 are 0.67 and 0.75, respectively, 9 and poor MacNew scores are associated with patients who are at high risk for poor outcomes. 4-6,8,9 One or more of the MacNew scales discriminates between patients with and without a previous myocardial infarction, with and without rehospitalization, and with and without surgery 4,5 while the global score and each scale discriminate between patients with heart failure and patients with either myocardial infraction or angina. 8 A recently published manuscript shows that MacNew differentiates between patients with angina who improve or deteriorate on the SF-36 health state question, patients with different levels of anginal severity, and patients treated conservatively from those with angioplasty or bypass surgery. A prospective cohort study published in 1998 provides evidence of the predictive validity of the MacNew with an odds ratio of 2.66 (95% confidence limits = 1.2 to 5.8) for an adverse event (death and rehospitalization) over 24 months among those patients in the lowest tertile compared to those in the highest tertile for baseline global MacNew HRQL. 6

DeVon and Ferrans also challenge the responsiveness of MacNew, which they defined as sensitivity or the ability to detect change over time. In the Hillers study, the MacNew is as or more responsive than a wide variety of other reference measures over a period of 12 months with effect sizes (eg, global score = 1.22) consistently greater than for the comparison questionnaires. 3 Evidence of responsiveness comes from comparisons of patients medically and invasively treated, 8 a more recently published prospective cohort study of patients with angina, 11 and from patients referred to cardiac rehabilitation after an acute myocardial infarction. 2 Moreover, DeVon and Ferrans have incorrectly interpreted the Lim study as examining responsiveness as the MacNew was completed by the patients in that study only at 6 months after discharge from the hospital. 4 Finally, data from two published studies suggest that the minimal important difference on the MacNew is 0.50 points on the 7-point scale. 8-10

Contrary to DeVon and Ferrans' conclusions, the published data provide substantial evidence for the reliability, validity, and responsiveness of the MacNew Heart Disease Health-related Quality of Life questionnaire in patients with myocardial infarction and in patients with angina. The MacNew is a useful instrument for investigators seeking a single disease specific HRQL instrument for comparing outcomes in patients with myocardial infarction and angina.

Neil Oldridge, PhD

L. Lim, PhD

G. Guyatt, MD

References