On the simultaneous relationship between the SF-6D index and satisfaction with life

Abstract

This paper aims to examine whether life satisfaction and health-related quality of life (HRQoL) are simultaneously related, as well as to quantify the bias that occurs if simultaneity is not accounted for. The study sample consisted of 870 respondents, representative of the Spanish adult general population. Using a simultaneous equations system —with the satisfaction with life scale (SWLS) and the SF-6D index as outcome variables—, we found a simultaneous association between life satisfaction and HRQoL, although this relationship is heterogeneous in individual characteristics such as age and sex. More important, the fact of estimating the relationship between life satisfaction and HRQoL under a unidirectional approach severely underestimates the effect of life satisfaction on HRQoL and, to a lesser degree, the reverse direction effect. In consequence, policy decisions intended to improve satisfaction with life or HRQoL can be wrong if they rely on unidirectional estimates. Another relevant implication of this research is that, as a result of the simultaneous relationship between life satisfaction and HRQoL, not only health interventions may increase satisfaction with life, but also policies that improve life satisfaction can lead to positive side effects on HRQoL.