“…Several time-invariant covariates (TICs) were considered, which have been recognized as important to the elder’s QoL in previous studies [ 10 , 11 , 13 ]. All covariates were collected in 2002, the first wave of data collection, which included 6 basic variables (age, gender - “male = 1, female = 0”; ethnicity - “Han = 1, non-Han = 0”; financial source - “enough = 1, not enough = 0”; smoking status - “current smoker = 1, not current smoker = 0”; drinking status - “current drinker = 1, not current drinker = 0”), 5 dietary variables (eat fresh fruit, eat meat, eat fish, eat egg, drink tea), 6 functional variables (bathing disability, dressing disability, toileting disability, transferring disability, continence disability, feeding disability) and 5 behavioral variables (do physical labor regularly, do housework, read newspapers/books, watch TV or listen to the radio, take part in some social activities).…”