Table 3 The estimation results of the second stage of the two-stage Heckman model (linear regression model)

1

Constant

0.146226

1.028661

0.14

0.887

2

Sex

0.4842669

0.63862

0.76

0.448

3

Marital status

0.5029652

0.3447849

1.46

0.145

4

Residence

-0.2201143

0.7845788

-0.28

0.779

5

Health insurance status

-0.2850529

0.7873446

-0.36

0.717

6

Income status

1.28558

0.2818277

4.56

0.000

7

Employment status

farmer (1)

Ref.

day laborer (2)

0.3342178

0.3499275

0.96

0.34

employee (3)

0.05269

0.5651545

0.09

0.926

Unemployed / Retired (4)

0.5117448

0.5564928

0.92

0.358

8

Educational status

0.3194747

0.2490572

1.28

0.2

9

Family size

-0.1002315

0.0501733

-2

0.046

10

Family head

0.0102589

0.3485236

0.03

0.977

11

Type of treatment center

0.2871371

0.3974957

0.72

0.47

12

Time spent with cataract

-0.2276048

0.2528077

-0.9

0.368

15

Number of observations

176

16

Inverse of mills ratio

-3,113,127

1,231,399

-2.53

0.011

17

Rho

-0.87078

18

Sigma

3,575,121

19

Wald chi2 (10)

46.21

20

Prob > chi2

0.0000