Table 1 The estimation results of the first stage of the two-stage Heckman model (probit model)

1

Constant

-0.442927

1.099755

-0.4

0.687

2

Sex

0.559064

0.6733877

0.83

0.406

3

Marital status

0.5864231

0.3669433

1.6

0.11

4

Residence

-0.315015

0.8064054

-0.39

0.696

5

Health insurance status

-0.285952

0.8120848

-0.35

0.725

6

Income status

1.351659

0.2943545

4.59

0

7

History of cataract surgery

-0.034654

0.3161874

-0.11

0.913

8

Employment status

farmer (1)

ref.

day-laborer (2)

0.4270107

0.3586724

1.19

0.234

employee (3)

0.1115752

0.5810532

0.19

0.848

unemployment/retired (4)

0.7058779

0.5838559

1.21

0.227

9

Educational status

0.4306897

0.2637001

1.63

0.102

10

Family size

-0.10075

0.0522524

-1.93

0.05

11

Family head

0.0173702

0.3665863

0.05

0.962

12

Familiarity with cataract

-0.004938

0.2705899

-0.02

0.985

13

Type of treatment center

0.4459119

0.4201671

1.06

0.289

14

Eye affected by cataract

right (1)

ref.

left (2)

0.0993777

0.2696921

0.37

0.713

both (3)

0.2109893

0.3586127

0.59

0.556

15

Time spent with cataract

-0.280168

0.2940173

-0.95

0.341

16

Preoperative visual acuity

-0.020275

0.6476432

-0.03

0.975

17

Self-reported eye complications

0.3423426

0.2627849

1.3

0.193

18

Self-reported systemic eye disease

0.1761758

0.2563241

0.69

0.492

19

Number of observations

217

20

Logarithm of probability

-78.78961

21

Pseudo R2

0.261

22

LR chi2 (21)

55.66

23

Prob > chi2

0