Testing relationships between clinical and non-clinical variables in xerostomia: a structural equation model of oral health-related quality of life.

OBJECTIVES: The aim of the study was to systematically test Wilson and Cleary's [Wilson IB, Cleary PD. JAMA 1995; 273: 59-65] conceptual model of the direct and mediated pathways between clinical and non-clinical variables in relation to the oral health-related quality of life (OHRQoL) of patients with xerostomia.
METHODS: We collected measures of clinical variables, self-reported symptoms, OHRQoL, global oral health perceptions and subjective well-being from 85 patients attending outpatient clinics.
RESULTS: Structural equation modelling indicated support for the dominant direct pathways between the main levels of the model; more severe clinical signs predicted worse patient reported symptoms; worse symptom perception was associated with a lower functional status as measured by OHRQoL; and lower OHRQoL predicted worse global oral health perceptions. There was no relationship between the final two levels of the model; global oral health perceptions and subjective well-being. Subjective well-being was associated instead with earlier non-adjacent levels; biological variables, symptoms and functional status. These pathways were both direct (salivary flow-well-being, functioning-well-being) and indirect (clinical signs-well being, symptom status-well-being). There were also indirect pathways; most notably, the impact of clinical variables on OHRQoL was mediated by patient reported symptom status.
CONCLUSIONS: The results support Wilson and Cleary's conceptual model of patient outcomes as applied to a chronic oral health condition and highlight the complexity of (inter)relationships between key clinical and non-clinical variables. Further conceptual development of the model is discussed, particularly the role of individual difference factors, and theoretical and methodological issues in OHRQoL research are highlighted.