Instrumental Variable Estimates of the Difference of In-Patient Mortality Between Urban and Rural Hospitals
| Tests for Instrumental Variables | IV Estimates of Hospital Type (Urban vs Rural) | ||||
|---|---|---|---|---|---|
| Instrumental Variable Model | Number of Groups for Instrumental Variable | Instrument F Statistic* | PValue for Overidentifying Restrictions Tests† | Coefficient β | PValue |
| IV = instrumental variable; APR-DRG = All Patient Refined Diagnosis-Related Group. | |||||
| * If an F statistic is less than 10, the instrumental variables are weak, given that instrumental variables have small partial correlation with the variable of interest. | |||||
| † If P <.05, one of the instrumental variables correlated with unmeasured confounders. | |||||
| Unadjusted | 2 | 1,540.16 | – | −0.02 | .34 |
| 4 | 642.65 | .65 | −0.03 | .16 | |
| 8 | 294.02 | .20 | −0.03 | .14 | |
| 12 | 184.31 | .13 | −0.03 | .13 | |
| Adjusted for demographic characteristics (age, sex, race, admission type, payer) | 2 | 1,568.24 | – | 0.013 | .58 |
| 4 | 652.86 | .80 | 0.0081 | .69 | |
| 8 | 289.74 | .22 | 0.0084 | .68 | |
| 12 | 187.14 | .10 | 0.0065 | .75 | |
| Adjusted for demographic characteristics and Charlson Comorbidity Index | 2 | 1,539.90 | – | 0.0090 | .69 |
| 4 | 642.51 | .92 | 0.0053 | .80 | |
| 8 | 289.72 | .25 | 0.0060 | .77 | |
| 12 | 184.29 | .12 | 0.0040 | .84 | |
| Adjusted for demographic characteristics and APR-DRG risk index | 2 | 1,694.27 | – | −0.0034 | .87 |
| 4 | 640.61 | .92 | −0.0069 | .72 | |
| 8 | 318.20 | .17 | −0.0032 | .87 | |
| 12 | 202.50 | .01 | −0.0063 | .74 | |