Table 2.
First-Stage Relationship between Merged Share and Premerge Share
| Without Hospital Referral Region Trends | With Hospital Referral Region Trends | |||||||
|---|---|---|---|---|---|---|---|---|
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | |
| Premerge share | 0.839 (0.020)*** | 0.838 (0.020)*** | 0.834 (0.021)*** | 0.835 (0.021)*** | ||||
| Premerge share × year 1 (post) | 0.823 (0.022)*** | 0.822 (0.021)*** | 0.819 (0.022)*** | 0.818 (0.022)*** | ||||
| Premerge share × year 2 (post) | 0.807 (0.023)*** | 0.805 (0.022)*** | 0.802 (0.024)*** | 0.801 (0.023)*** | ||||
| Premerge share × year 3 (post) | 0.817 (0.022)*** | 0.815 (0.022)*** | 0.812 (0.023)*** | 0.811 (0.023)*** | ||||
| Premerge share × year 4 (post) | 0.807 (0.021)*** | 0.806 (0.021)*** | 0.803 (0.022)*** | 0.802 (0.022)*** | ||||
| Premerge share × year 5+ (post) | 0.794 (0.023)*** | 0.793 (0.023)*** | 0.781 (0.025)*** | 0.782 (0.025)*** | ||||
| R2 | 0.92 | 0.92 | 0.92 | 0.92 | 0.93 | 0.93 | 0.92 | 0.92 |
| F-statistic for instrument(s) | 1730.85 | 1761.39 | 323.86 | 331.03 | 1575.2 | 1600.73 | 296.07 | 301.49 |
| Control variables | X | X | X | X | ||||
| Observations | 47,396 | 47,396 | 47,396 | 47,396 | 47,396 | 47,396 | 47,396 | 47,396 |
Notes. Robust standard errors in parentheses.
*
Significant at 10%;
**
Significant at 5%;
***
Significant at 1%.
Zip codes are only included if they have 15 or more discharges in every quarter. All regressions include quarter and zip code fixed effects and are weighted by the number of heart disease discharges. Standard errors are clustered by zip code. Control variables include the percentage of discharges with demographic characteristics such as race, gender, and age categories; with expected payer such as Medicare and private insurance; with comorbidities such as hypertension, diabetes, and heart failure; admission through the ER; and a constant.