Comparison between different instruments for measuring health-related quality of life in a population sample, the WHO MONICA Project, Gothenburg, Sweden: an observational, cross-sectional study

OBJECTIVE: The general aim was to meet the need for empirical comparative studies of health-related quality of life (HRQoL) assessment instruments, by evaluating and comparing the psychometric properties and results of three different, widely used, generic HRQoL instruments in a population sample. The specific aims were to evaluate the subscales of the different instruments that measure the same domain and to assess the association between the HRQoL measures and a single-item self-rated health scale. DESIGN: An observational cross-sectional study. SETTING: A population-based sample from Gothenburg, Sweden, was studied in 2008 in the WHO MONItoring of trends and determinants for CArdiovascular disease. PARTICIPANTS: A total of 414 subjects were included, 77% women, age range 39–78 years. INTERVENTIONS: The Nottingham Health Profile (NHP), the Short Form-36 questionnaire (SF-36), the Psychological General Well-Being Index (PGWB) and a self-rated health scale were used. OUTCOME MEASURES: Scores were analysed for their psychometric properties, internal consistency (Cronbach’s α), construct validity (Spearman’s rank correlations and R(2) coefficients) and discriminative ability for the presence of self-rated ill-health. RESULTS: PGWB and SF-36 had higher Cronbach’s α scores than NHP. All correlations calculated between the subscales that were conceptually similar were significant (p<0.01). All subscales could differentiate the presence of self-rated ill-health according to the self-rated health scale (p<0.001). The self-rated health scale correlated strongly with all of the three HRQoL instruments used. CONCLUSIONS: There was a high concordance between the instruments within each domain that was conceptually similar. All three HRQoL instruments (PGWB, SF-36 and NHP) could discriminate the presence of self-rated ill-health. The simple and quick self-rated health scale correlated strongly with the more time-consuming PGWB, SF-36 and NHP. The result supports the existence of a strong association between the self-rated health scale and HRQoL in the general population.