Linear probability model | (1) | (2) | (3) | (4) | (5) |
Delivery volume | 0.003*** (0.003 to 0.004) | 0.000 (0.000 to 0.000) | −0.025*** (−0.026 to –0.024) | 0.003 (−0.003 to 0.009) | −0.021*** (−0.022 to –0.020) |
Patient characteristics | √ | √ | |||
Institutional characteristics | √ | √ | |||
Regional characteristics | √ | √ | |||
Year | √ | √ | √ | √ | |
Logistic regression model | (6) | (7) | (8) | (9) | (10) |
Delivery volume | 0.003*** (0.003 to 0.004) | 0.001 (−0.001 to 0.001) | −0.021*** (−0.022 to –0.020) | 0.001*** (0.001 to 0.002) | −0.015*** (−0.016 to –0.014) |
Patient characteristics | √ | √ | |||
Institutional characteristics | √ | √ | |||
Regional characteristics | √ | √ | |||
Year | √ | √ | √ | √ | |
Ordinary IV model | (11) | (12) | (13) | (14) | (15) |
Delivery volume | −0.027*** (−0.029 to –0.026) | −0.054*** (−0.056 to –0.052) | −0.153*** (−0.158 to –0.148) | −0.091*** (−0.095 to –0.087) | −0.133*** (−0.139 to –0.127) |
Patient characteristics | √ | √ | |||
Institutional characteristics | √ | √ | |||
Regional characteristics | √ | √ | |||
Year | √ | √ | √ | √ | |
First-stage F statistic | 48 654 | 39 989 | 27 459 | 16 590 | 20 966 |
First-stage adjusted R 2 | 0.129 | 0.155 | 0.732 | 0.293 | 0.747 |
Test for endogeneity (p value) | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 |
IV-logistic model | (16) | (17) | (18) | (19) | (20) |
Delivery volume | −0.032*** (−0.033 to –0.030) | −0.066*** (−0.068 to –0.063) | −0.198*** (−0.204 to –0.192) | −0.122*** (−0.126 to –0.117) | −0.162*** (−0.169 to –0.155) |
Patient characteristics | √ | √ | |||
Institutional characteristics | √ | √ | |||
Regional characteristics | √ | √ | |||
Year | √ | √ | √ | √ | |
First-stage F statistic | 48 654 | 39 989 | 27 459 | 16 590 | 20 966 |
First-stage adjusted R 2 | 0.129 | 0.155 | 0.732 | 0.293 | 0.747 |
Test for endogeneity (P value) | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 |
95% CIs in parentheses.
The average marginal effects of logistic regression models and IV-logistic models were reported.
Significant: ‘***’p<0.001, ‘**’ p<0.01, ‘*’ p<0.05.
IV, instrumental variable.