Comparative vs global self-rated health: associations with age and functional ability

Abstract

This study examined the relationship of age and functional ability with comparative (age-referential) and global self-rated health (SRH), and the possible effect of selection bias. The focus is on differences between these questions and on the consequences which these differences have in research. The data came from the second wave of the Tampere Longitudinal Study on Ageing (TamELSA), consisting of 830 persons aged 60-99 years. The associations of both self-rated health measures with age and functional ability were examined using multinomial regression analyses. People with increasing age, particularly over 80-year-old, are inclined to rate their health better than that of their age peers. The association of older age with better comparative SRH became even stronger after adjustment for functional ability, chronic diseases and sociodemographic factors. The relation of older age with global SRH was weaker than that with age-referential SRH. By contrast, functional ability was more strongly associated with global than with comparative SRH. Our results suggest that comparative and global self-rated health cannot be used interchangeably. The comparative measure is more strongly "calibrated" by age. Therefore, when SRH is used as a measure in survey studies or in clinical settings, the global question should be preferred.