Obesity Epidemiology

236 EPIDEMIOLOGIC STUDIES OF CONSEQUENCES OF OBESITYMeasurement of HRQOLMeasures in Adult PopulationsA variety of instruments have been used to assess the relationship between obesity andHRQOL. In this section, we describe some of the most commonly applied instruments,as well as their psychometric properties.The Short-Form 36 (SF-36) is a widely used 36-item questionnaire originally appliedin the RAND Medical Outcomes Study. 17 The SF-36 taps into eight core domains: physicalfunctioning (PF), role limitations due to physical health problems (RP), bodily pain(BP), general health (GH), vitality (VT), social functioning (SF), role limitations due toemotional health (RE), and mental health (MH). Each scale is scored from 0 to 100, withhigher scores indicating higher HRQOL. The PF, RP, BP, and GH scales can be used inturn to construct a Physical Component Summary (PCS) score, while the VT, SF, RE,and MH scales are used to calculate a Mental Component Summary (MCS) score. Theoriginal English version of the SF-36 has been translated into other languages, includingSpanish, Swedish, and Chinese. Good internal consistency reliability, test-retest reliability,and construct validity have been documented for the SF-36 in both clinical andgeneral population samples across multiple countries. 18-22The Short-Form 12 (SF-12) and Health Status Questionnaire (HSQ-12) are both12-item shortened versions of the SF-36, which measure the same eight domains as theSF-36, and which likewise enable PCS and MCS scores to be calculated. Like the SF-36,psychometric studies have demonstrated the reliability and validity of these measures ingeneral population samples, including in older age groups. 23-25The Obesity Specific Quality of Life (OSQOL) scale is an 11-item scale that encompassesfour dimensions of self-rated health: physical state, vitality, relations with otherpeople, and psychological state. In a random sample of 500 obese and 500 nonobeseindividuals in the general population, the scale exhibited acceptable internal consistencyreliability (Cronbach’s alpha = 0.77) as well as content and construct validity. 26Four items comprise the Centers for Disease Control and Prevention HRQOL-4instrument, 27 corresponding to general health status, recent physical health status based onthe number of physically unhealthy days during the past month, recent mental health status,and recent number of days of activity limitation during the past month. In both healthyand disabled populations, each of these items has been shown to possess good constructand criterion validity, 28-30 as well as moderate-to-high 2-week test-retest reliability. 31The Quality of Well-Being (QWB) scale quantifies HRQOL by combining preferenceweightedvalues for symptoms and functioning, and yields a numerical expression ofwell-being, ranging from 0 for death to 1 for optimal functioning. 32 Internal consistencyreliability, test-retest reliability, along with content, construct, and criterion validity haveall been demonstrated in general population and clinical samples. 33-35The World Health Organization Quality of Life Questionnaire abbreviated version(WHOQOL-BREF) is a 26-item instrument comprised of four domains (physical, psychological,social relations, and the environment) that can also be used to assess HRQOL.Each of the domains has a possible score ranging from 0 (poor HRQOL) to 20 (excellentHRQOL). Cross-cultural surveys of adult respondents in 23 countries have shown theWHOQOL-BREF to possess good to excellent psychometric properties of reliability aswell as validity in both general population and clinical samples. 36The EuroQol EQ-5D categorizes a respondent’s health according to the followingdimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression.37 This measure can be used to provide a self-rating of health status based on a visual