“…The primary predictors of the aforementioned dependent variables were the follow-up measures at two, four, and six months and each follow-up measure was compared with baseline measure to determine the effects of hyaluronic acid. In all of the mixed effects models, gender, marital status, comorbidities (hypertension, diabetes mellitus, heart disease, depression, and cancer), and age were controlled because these factors may be confounders in patient-reported outcomes (Chang et al, 2017, Huang et al, 2018, Lee et al, 2017a, Lee et al, 2017b, Lee et al, 2018). Specifically, linear effect was estimated for age, and categorical effects were estimated for other independent variables.…”