Table 2 Sample characteristics, second and third waves (no. (%), mean (95% CI))
| Â | Second wave (2006) | Third wave (2009) | ||||
|---|---|---|---|---|---|---|
Low income | High income | P value | Low income | High income | P value | |
(28–580 USD) | (580–4077 USD) | (28–592 USD) | (592–4087 USD) | |||
N | 711,590 | 2,132,744 | Â | 690,034 | 2,063,190 | Â |
Place of residence | ||||||
 Urban | 435,359 (61.2%) | 1,280,870 (60.1%) | <.001 | 429,769 (62.3%) | 1,256,949 (60.9%) | <.001 |
 Suburban | 227,213 (31.9%) | 630,682 (29.6%) | 213,573 (31.0%) | 598,487 (29.0%) | ||
 Rural | 49,018 (6.9%) | 221,192 (10.4%) | 46,692 (6.8%) | 207,754 (10.1%) | ||
Occupation categorya | ||||||
 1 | 146,102 (20.5%) | 357,037 (16.7%) | <.001 | 143,267 (20.8%) | 351,295 (17.0%) | <.001 |
 2 | 181,885 (25.6%) | 887,469 (41.6%) | 159,376 (23.1%) | 846,449 (41.0%) | ||
 3 | 19,462 (2.7%) | 445,932 (20.9%) | 20,309 (2.9%) | 446,322 (21.6%) | ||
 4 | 4097 (0.6%) | 433,736 (20.3%) | 3769 (0.5%) | 412,798 (20.0%) | ||
 5 | 17,015 (2.4%) | 626 (0.0%) | 18,369 (2.7%) | 155 (0.0%) | ||
 6 | 343,029 (48.2%) | 7944 (0.4%) | 344,944 (50.0%) | 6171 (0.3%) | ||
Elixhauser comorbidity index | ||||||
 0 | 501,825 (70.5%) | 1,577,535 (74.0%) | <.001 | 484,908 (70.3%) | 1,533,179 (74.3%) | <.001 |
 1–3 | 204,453 (28.7%) | 546,943 (25.6%) | 201,450 (29.2%) | 524,644 (25.4%) | ||
  ≥ 4 | 5312 (0.7%) | 8266 (0.4%) | 3676 (0.5%) | 5367 (0.3%) | ||
 Outpatient visitsb | 12.24 (12.21–12.27) | 11.63 (11.61–11.64) | <.001 | 12.06 (12.03–12.09) | 11.53 (11.51–11.54) | <.001 |
 Inpatient staysb | 0.137 (0.136–0.138) | 0.104 (0.104–0.105) | <.001 | 0.130 (0.129–0.130) | 0.101 (0.101–0.101) | <.001 |
 Physician density of residenceb | 1.728 (1.725–1.732) | 1.835 (1.832–1.837) | <.001 | 1.820 (1.817–1.824) | 1.894 (1.891–1.896) | <.001 |