Interpretation of a Self-Esteem Subscale for Erectile Dysfunction by Cumulative Logit Model
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Interpretation of a Self-Esteem Subscale for Erectile Dysfunction by Cumulative Logit Model
Joseph C. Cappelleri, MS, PhD, MPH Director—Biostatistics, Pfizer Inc, Global Research & Development, Groton, Connecticut Stephen S. Bell, PhD Senior Partner, Bell, Falla and Associates, Norwalk, Connecticut Richard L. Siegel, MD Senior Medical Director, Sexual Health Team, Pfizer Pharmaceuticals, Pfizer Inc, New York, New York
Key Words Impotence; Self-concept; Cumulative logit model; Quality of life; Psychometrics Correspondence Address Joseph C. Cappelleri, Pfizer Inc, Global Research & Development, Eastern Point Road, MS 8260–2222, Groton, CT 06340 (e-mail: joseph.c.cappelleri@ pfizer.com). This work was supported with funding from Pfizer Inc.
A content-based interpretation of a health status measure uses an item, along with its response choices, internal to the measure to understand the meaning of its scores. We applied a cumulative logit model to content-based interpretation of a validated self-esteem subscale (four items) for men with erectile dysfunction (score range: 0 to 100, where higher scores indicate a more favorable response). Data were obtained from a nontreatment cross-sectional study with 98 men with erectile dysfunction and 94 controls. The ordinal response item “I had good self-esteem” over the past 4 weeks (1 = Almost never/never, 2 = A few times, 3 = Sometimes, 4 = Most times, 5 = Almost always/Al-
INTRODUCTION Measures of health status have been used to define functional capacity or, alternatively, a state of physiological and psychological functioning, or well-being. They tend to include items with ordinal categories of response to patientreported outcomes (including, but not limited to, health-related quality of life, treatment satisfaction, symptoms) and clinician-reported outcomes. Examples of widely used health status measures include the Hamilton Rating Scale for Depression (1), the Hospital Anxiety and Depression Scale (2), the 36-item short form (SF36) (3), the European Organization for the Treatment of Cancer (EORTC) quality-of-life instrument (4), and the International Index of Erectile Function (5), among others. Given the prevalence and influence of health status measures in medical care, especially in chronic diseases, interpretation of scores and changes in scores from validated health status measures have become crucial for understanding the meaning and relevance of these scores for effective decision making. Useful interpretation of such scores can be valuable in designing studies, evaluating interventions, informing
ways) was regressed on the self-esteem subscale score to which the item belongs. The proportional odds assumption was not refuted (P = .085) and supported graphically. At relatively high self-esteem scores (65+), the estimated probability of reporting good self-esteem (ie, good self-esteem most of the time or almost always/always) was 68% or more. For a 10point increase (eg, 65 to 75), the odds of reporting good self-esteem increased slightly more than threefold (
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