Income and Oral and General Health-Related Quality of Life: The Modifying Effect of Sense of Coherence, Findings of a Cross-Sectional Study

Objectives To investigate whether a strong sense of coherence (SOC) modifies the association between low-income and oral and general health-related quality of life (OHRQoL and HRQoL, respectively) among a South Australian population sample; and to explore the main and interaction effects of income and SOC on OHRQoL and HRQoL. Methods Baseline data from the Dental Care and Oral Health Study (DCOHS, a South Australian representative study, 2015–2016) were used for cross-sectional analysis (n = 3,786). Four multivariable factorial ANOVA models were applied to assess the effect measure modification, main effects, and interaction of income and SOC on OHRQoL (measured using the OHIP-14) and HRQoL (measured using the EQ-5D-3L). Results Income and SOC had small main effects on OHRQoL. Income had a small effect and SOC had an intermediate effect on HRQoL, meaning that individuals with strong SOC had better OHRQoL and HRQoL in all income categories. Also, high-income participants had better OHRQoL and HRQoL. The interaction between income and SOC was statistically significant on HRQoL. Among participants from low-income group, those with strong SOC had better OHRQoL (mean = 8.8, 95% CI[7.9, 9.7]) and HRQoL (mean = 1.1, 95% CI[1.0, 1.3]) than others with weak SOC (OHIP-14 mean = 12.7, 95% CI[11.7, 13.6]) and (EQ-5D-3L mean = 2.0, 95% CI[1.9, 2.2]). Conclusion The findings showed the main effects and interaction between SOC and income on OHRQoL and HRQoL. Income had different effects on OHRQoL and HRQoL depending on whether SOC was strong or weak. Findings suggested that strong SOC modified the association between low-income and OHRQoL and HRQoL.