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The purposes of this analysis were to evaluate the construct validity of the EQ-5D and compare responses on the EQ-5D with the Physical Component Summary (PCS-12) and Mental Component Summary (MCS-12) scores of the SF-12 Health Survey.Data were collected via a survey instrument mailed to 4,200 randomly selected subjects in the province of Alberta, Canada. The instrument contained the EQ-5D and SF-12 health surveys, with additional questions eliciting clinical and demographic information from the respondents.1555 respondents returned mailed questionnaires; 606 questionnaires were returned undeliverable. The SF-12 summary scores were calculated for 1,380 respondents. Analysis of the EQ-5D responses by demographic variables found significant differences among categories of age, gender, and self-reported chronic medical conditions. Corresponding dimensions and summary scores were more strongly related (eg, mobility and PCS-12; F ratio = 598.3, P < 0.001) than dissimilar dimensions (eg, mobility and MCS-12; F ratio = 18.8, P < 0.001). The EQ-5D index scores were moderately correlated with SF-12 summary scores (r = 0.41 for MCS-12 and r = 0.68 for PCS-12). For subjects reporting no problems on the EQ-5D, PCS-12 and MCS-12 scores were significantly lower for people reporting medical problems or feelings of depression.The results of this investigation generally supported the validity of the EQ-5D. However, an important ceiling effect was observed for the EQ-5D in this sample. The combination of the EQ-5D and SF-12 provides relatively broad coverage of important health domains and scores for various purposes.