sentence: Multiple linear regression ( MLR ) analysis was used to regress the APSs ( dependent variable ) using the following explanatory factors : age groups ( reference category : 65 – 69 ) , females ( reference category : males ) , civil status ( reference category : single ) , education ( reference category : elementary school ) , annual income , pain intensity , pain frequency ( reference category : seldom ) , total score of GWBS , EQ-5D-VAS , and overall life satisfaction .