Table 1.
Characteristics of the Nurses' Health Study Participant and Medicare Control Cohorts, Before and After Propensity Score Matching
| Covariate | NHS participants | Medicare controls (before matching) | Medicare controls (after matching) | Std. differencea(after matching) |
|---|---|---|---|---|
| N | 47,194 | 2,834,525 | 47,194 | |
| Age as of January 1, 2012, mean (std) | 76.6 (6.8) | 76.1 (8.1) | 76.5 (7.5) | 0.02 |
| Race, N (%) | ||||
| White | 46,036 (97.6) | 2,457,989 (86.7) | 46,242 (98.0) | −0.03 |
| Black | 696 (1.5) | 218,150 (7.7) | 588 (1.3) | 0.03 |
| Other | 438 (0.9) | 111,084 (3.9) | 345 (0.7) | 0.02 |
| Hispanic | 24 (0.1) | 47,302 (1.7) | 19 (0.0) | 0.01 |
| Socioeconomic status | ||||
| Dual eligible, N (%) | 1,187 (2.5) | 490,890 (17.3) | 948 (2.0) | 0.04 |
| Median income,b mean (std) | $66,374 ($24,724) | $57,438 ($23,030) | $66,264 ($25,302) | 0.01 |
| Census region, N (%) | ||||
| Northeast | 22,517 (47.7) | 552,404 (19.5) | 22,118 (46.9) | 0.02 |
| South | 11,832 (25.1) | 1,085,094 (38.3) | 12,253 (26.0) | −0.02 |
| Midwest | 7,044 (14.9) | 695,434 (24.5) | 7,106 (15.1) | 0.00 |
| West | 5,801 (12.3) | 501,593 (17.7) | 5,717 (12.1) | 0.00 |
| Health status | ||||
| Elixhauser comorbidity count = 0, N (%) | 11,962 (25.4) | 780,034 (27.5) | 12,637 (26.8) | −0.03 |
| Elixhauser comorbidity count = 1–2, N (%) | 21,211 (44.9) | 1,174,156 (41.4) | 21,977 (46.6) | −0.03 |
| Elixhauser comorbidity count ≥3, N (%) | 14,021 (29.7) | 880,335 (31.1) | 12,580 (26.7) | 0.07 |
| Overall Elixhauser comorbidity count, mean (std) | 1.98 (2.1) | 2.00 (2.1) | 1.79 (1.8) | 0.05 |
| Comorbidity count if Elixhauser count ≥3 mean (std) | 4.51 (1.9) | 4.52 (1.8) | 4.22 (1.6) | 0.09 |
Demographic and health status data before and after propensity score matching are displayed above.
a
Standardized difference after propensity score matching is calculated as the standardized difference of means between the two groups. Absolute values greater than or equal to 0.10 were interpreted as a statistically significant difference between the two cohorts.
b
Median income is derived from patient zip code, not individual level data.
NHS, Nurses' Health Study.