Original articles
A new surrogate variable for erectile dysfunction status in the Massachusetts male aging study

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Abstract

Erectile dysfunction (ED) is the subject of a vast clinical literature, but little information has been gathered from random samples of the general public. The Massachusetts Male Aging Study (MMAS) addressed this important aspect of men's health. The MMAS was conducted in two waves, with baseline data collection in 1987–1989 and follow-up in 1995–1997. Subsequent to the baseline MMAS survey, a consensus developed that subjective measures are optimal for defining ED. Unfortunately, the baseline questionnaire did not ask subjects directly about their erectile functioning. Thus, we previously assigned the MMAS subjects a degree of impotence at baseline using a series of related questions, employing a discriminant formula constructed from a separate sample of urology clinic patients. At follow-up the men classified themselves directly in addition to answering the original series of related questions. In the present article, we report the results of a new discriminant function, based on the MMAS men at follow-up. We also compare the two methods and discuss our reasons for preferring the internally calibrated method.

Introduction

Erectile dysfunction (ED) is the subject of a vast clinical literature, but little available information on the epidemiology of the condition is based on random samples of community-dwelling individuals. The Massachusetts Male Aging Study (MMAS) addressed this important aspect of men's health through a population-based sampling frame, conducting in-person interviews in the subjects' homes. The MMAS was a cohort study conducted in two waves, with baseline data collection in 1987–1989 and follow-up in 1995–1997.

The common term “impotence” has been replaced in the last 5 years by “erectile dysfunction” at the urging of a National Institutes of Health consensus panel that convened in 1992, halfway between the two waves of the MMAS. The panel published a working definition of ED [1]—“the persistent inability to attain and maintain a penile erection adequate for satisfactory sexual performance”—and called for “major research efforts” to improve diagnostic classification for epidemiologic purposes. It bears emphasizing that this definition is based on a subjectively identified state for each man that depends on his perception of satisfactory sexual performance.

It was left to the research community to operationalize the NIH consensus definition in further studies. Clinical questionnaires have been developed (e.g. 2, 3), but asking sensitive questions in a primary provider's office, once the patient has sought treatment, is far different from administering a standardized instrument as a stranger in the field.

In this report we describe and compare two techniques by which we have classified the subjects in the MMAS regarding their erectile dysfunction status. These include the original classification technique based on data from a separate clinic sample and a new technique based on data from the follow-up wave of the MMAS. The techniques have been adapted to meet the rapidly evolving views and improved understanding of erectile dysfunction in the clinical community, while maintaining a balance between external and internal validity.

Section snippets

Sampling and data collection

The baseline Massachusetts Male Aging Study was a random sample, cross-sectional, multidisciplinary survey of health and aging in men, conducted in 11 cities and towns in the area of Boston, MA. Communities were randomly selected with probabilities proportional to population within each of six strata defined by community size and median income. Men born between 1917 and 1946 were drawn at random from the annual state census listings. Sampling fractions were adjusted to produce a uniform age

Description of the discriminant functions

As reported by Feldman et al. [8], the clinic method had the following characteristics. It used nine questions, including questions about how often the men had erections, sexual intercourse or activity, whether they had trouble getting or keeping an erection, how frequently they woke from sleep with a full erection, whether their sexual activity was as frequent as they wished, and several questions about their satisfaction with their sex life and relationships. The questions are presented in

Discussion

The fact that the two methods showed different associations with covariates and the fact that the weighted kappa indicated a less-than-substantial agreement between the two methods are evidence that they have different meanings. Presented with these two alternative methods, the natural question is: Which one is preferable? Because we do not know the true ED status of the men at baseline, we cannot determine which method is more valid (i.e., closer to the truth). In other words, we cannot

Summary

The epidemiology of erectile dysfunction is a rapidly developing field of study; it is often the case that rich and valuable data sets do not contain a measure that turns out to be of later interest. In this case, definitions of ED changed during the course of the MMAS. In addition, over time, thinking about the causes of ED has shifted from attributing ED primarily to psychogenic causes to attributing ED to organic causes, and it is now well-accepted that ED can be assessed subjectively.

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