Table 1 Assignment of independent variables

Age

60–74 = 1, 75–89 = 2, 90 or older = 3

Educational level

Primary and below = 1, Middle school = 2, Tertiary education = 3, Undergraduate and above = 4

Type of work

Mental labor = 1, Physical labor = 2, Both = 3

Marital status

Married(H1 = 0,H2 = 0,H3 = 0), Singlehood(H1 = 1,H2 = 0,H3 = 0)

Widowed(H1 = 0,H2 = 1,H3 = 0), Divorce(H1 = 0,H2 = 0,H3 = 1)

Habitation

Solitude(J1 = 0,J2 = 0,J3 = 0), Living with spouse only(J1 = 1,J2 = 0,J3 = 0)

Living with children and spouse(J1 = 0,J2 = 1,J3 = 0), Others ( such as pension institutions)(J1 = 0,J2 = 0,J3 = 1)

Family relations

Not harmony = 1, Normal harmony = 2, More harmonious = 3, Very harmonious = 4

Daily exercise

No = 0, Yes = 1

Sleep quality

Good = 1, Normal = 2, Poor = 3

Chronic disease

Less than 1 kind = 1, Greater than or equal to two = 2

Personal income

Income is greater than expenditure = 1, Income approximately equal to expenditure = 2, Income less than expenditure = 3, No income = 4

Medical burden

No burden = 1, Some burdens = 2, Burden heavier = 3

Total score of loneliness

Initial value