A comparison of four approaches to measuring health outcome

Objectives. To compare four diverse approaches to measuring patient perceptions about health outcomes; the SF-36 Health Survey; clinically derived condition specific instruments; daily time trade-off (DTTO); patient generated index (PGI). The relationship between the instruments and their responsiveness to changes in Health Related Quality of Life (HRQL) was assessed. Results. The response rate exceeded 75% (1327 respondents). The SF-36 had Cronbach's Alpha values above the criterion of 0.7. Test-retest estimates were above 0.7 for al but the role-limitations scales which were above the criterion of 0.5. The specific instruments produced Alpha values and test-retest estimates above 0.7. The DTTO and PGI produced estimates of reliability above 0.5. Evidence for the construct validity of the SF-36 was demonstrated by the differences in scale scores between the general population and four condition-specific groups. Evidence for the construct validity of the specific instruments and PGI was demonstrated by the significant moderate levels of correlation with the SF-36. Evidence for the validity of all four approaches was demonstrated by patient scores behaving as predicted in relation to condition-specific and sociodemographic variables. Comparisons of the four approaches show that the relationship between them is condition dependent. Score changes for the SF-36, specific instruments and PGI were significantly related to self reported health transition. The SRMs for the specific instruments were significantly greater than those for the SF-36. Conclusions. These results demonstrate that the SF-36 has similar properties in United Kingdom patient populations as those in the United States and is satisfactory for comparisons of groups. The clinically derived approach is recommended for constructing instruments where no suitable condition-specific instrument exists. These two approaches are recommended for use as part of a package of instruments for assessing health outcomes.