Table 4:
DiD Regression Analyses: Effect of Damage Caps on Outpatient Laboratory and Radiology Spending
| No |
Patient * Zip |
Physician * Zip |
|||||||
|---|---|---|---|---|---|---|---|---|---|
| Patient or Physician FE |
(1) |
(2) |
(3) |
(4) |
(5) |
(6) |
(7) |
(8) |
(9) |
| Variables | Lab | Radiology | Both | Lab | Radiology | Both | Lab | Radiology | Both |
| Panel A: Simple DiD | |||||||||
| Damage cap dummy | 3.58 | 10.63*** | 14.21** | 5.13 | 12.36*** | 17.53** | 0.43 | 3.47*** | 3.90** |
| (4.04) | (2.93) | (5.92) | (4.32) | (3.34) | (6.654) | (1.11) | (0.94) | (1.84) | |
| R2 | 0.20 | 0.12 | 0.19 | 0.61 | 0.50 | 0.59 | 0.21 | 0.12 | 0.19 |
| Observations | 13,524,405 | 13,524,405 | 13,524,405 | 10,748,076 | 10,748,076 | 10,748,076 | 64,462,133 | 64,462,133 | 64,462,133 |
| Panel B: Distributed Lags | |||||||||
| Cap year adoption and after | 1.43 | 4.08* | 5.506 | 1.00 | 4.56* | 5.57 | −0.44 | −2.05*** | −2.49 |
| (2.30) | (2.21) | (3.93) | (2.16) | (2.43) | (4.14) | (1.01) | (0.68) | (1.54) | |
| Cap Year 1 or after | −0.75 | 6.39** | 5.636 | 0.61 | 7.05** | 7.66* | 0.27 | 5.27*** | 5.54** |
| (1.40) | (3.03) | (3.34) | (1.48) | (3.13) | (3.83) | (1.27) | (1.41) | (2.44) | |
| Cap year 2 or after | 2.24 | 2.53 | 4.771 | 2.68 | 2.87 | 5.55 | 0.71 | 1.35** | 2.05* |
| (2.27) | (2.43) | (3.95) | (2.28) | (2.93) | (4.65) | (0.56) | (0.64) | (1.00) | |
| Cap Year 3 or after | 2.54 | 2.749** | 5.29 | 1.25 | 2.63 | 3.88 | 0.62 | 1 24*** | 1.86** |
| (2.42) | (1.25) | (3.44) | (2.62) | (1.63) | (3.86) | (0.55) | (0.41) | (0.90) | |
| Cap Year 4 or after | −1.08 | −5.905 | −6.98 | 0.59 | −4.88 | −4.28 | 0.23 | −0.80 | −0.57 |
| (3.26) | (3.59) | (6.19) | (2.16) | (3.89) | (4.67) | (0.52) | (0.99) | (1.234) | |
| Sum of coefficients | 4.37 | 9.85*** | 14.22** | 6.14 | 12.23*** | 18.37** | 1.39 | 5.01*** | 6.41** |
| (5.50) | (3.49) | (6.49) | (6.63) | (3.82) | (7.37) | (1.78) | (1.32) | (2.53) | |
| R2 | 0.20 | 0.12 | 0.19 | 0.61 | 0.49 | 0.59 | 0.21 | 0.12 | 0.19 |
| Observations | 13,039,123 | 13,039,123 | 13,039,123 | 11,209,653 | 11,209,653 | 11,209,653 | 64,462,133 | 64,462,133 | 64,462,133 |
| Percentage change | +2.0% | +5.1% | +3.4% | +2.8% | +6.3% | +4.4% | +2.4% | +10.3% | +6.0% |
Notes: Panel A: Difference-in-differences regressions for indicated outpatient Medicare spending categories per enrollee, per calendar year, on damage cap dummy and covariates. Coefficient on damage cap dummy are multiplied by 4, so coefficients provide estimated effect of cap on annual spending per patient. Coefficients on covariates are suppressed, but presented in the Supporting Information (Table App 3).
Panel B: Distributed lag regressions for indicated Medicare spending categories per enrollee, per year. Distributed lag analysis in a given year. Coefficients on covariates are suppressed.
Both panels: Column (1): laboratory spending; Column (2): radiology spending; Column (3): combined laboratory and radiology spending. Sample, main variables, covariates, and fixed effects are same as corresponding specifications (using patient * zip FE, physician * zip FE, or neither) in Table 2; coefficients on covariates are suppressed. Amounts in 1999 $s. Standard errors, clustered on state, in parentheses.
indicates statistical significance at the 10 percent, 5 percent, and 1 percent level, respectively. Significant results, at 5 percent level or better, in boldface. Percentage change is relative to base rate in 2002 for New-Cap states.