Covariates Additional items addressing demographic and disease characteristics were developed based on clinical experience and literature review, and were collected at study entry via patient interviews and medical records. Demographic data included sex, age, marital status, education level, religion, household status, monthly income, and certain lifestyle factors, such as smoking, exercise habits, and presence of sleep disturbances. Smoking status was recorded as "non-smoker" or "current or ex-smoker." Those who exercised regularly (i.e., weekly) were classified as having "exercise habits." Sleep disturbances were defined as waking up at night more than twice without external factors during the week before the interview. Disease characteristics included the presence of chronic disease (i.e., stroke, hypertension, heart disease, renal disease, or cancer), medication regimen, and duration of diabetes.