| Fourth Wave (2012) | Fifth Wave (2015) | ||||
---|---|---|---|---|---|---|
Low income | High income | P value | Low income | High income | P value | |
(32–650 USD) | (650–5966 USD) | (37–694 USD) | (694–6125 USD) | |||
N | 661,473 | 1,983,195 | Â | 633,181 | 1,905,065 | Â |
Place of residence | ||||||
 Urban | 407,621 (61.6%) | 1,192,881 (60.1%) | <.001 | 388,749 (61.4%) | 1,141,552 (59.9%) | <.001 |
 Suburban | 209,417 (31.7%) | 592,433 (29.9%) | 201,148 (31.8%) | 576,237 (30.2%) | ||
 Rural | 44,435 (6.7%) | 197,881 (10.0%) | 43,284 (6.8%) | 187,276 (9.8%) | ||
Occupation categorya | ||||||
 1 | 141,949 (21.5%) | 344,832 (17.4%) | <.001 | 146,710 (23.2%) | 394,423 (20.7%) | <.001 |
 2 | 154,881 (23.4%) | 803,378 (40.5%) | 135,848 (21.5%) | 763,839 (40.1%) | ||
 3 | 15,196 (2.3%) | 445,780 (22.5%) | 10,742 (1.7%) | 389,919 (20.5%) | ||
 4 | 3676 (0.6%) | 384,836 (19.4%) | 3134 (0.5%) | 354,372 (18.6%) | ||
 5 | 23,255 (3.5%) | 22 (0.0%) | 25,266 (4.0%) | 8 (0.0%) | ||
 6 | 322,516 (48.8%) | 4347 (0.2%) | 311,481 (49.2%) | 2504 (0.1%) | ||
Elixhauser comorbidity index | ||||||
 0 | 436,629 (66.0%) | 1,405,986 (70.9%) | <.001 | 406,967 (64.3%) | 1,333,529 (70.0%) | <.001 |
 1–3 | 221,470 (33.5%) | 572,353 (28.9%) | 223,665 (35.3%) | 567,905 (29.8%) | ||
  ≥ 4 | 3374 (0.5%) | 4856 (0.2%) | 2549 (0.4%) | 3631 (0.2%) | ||
 Outpatient visitsb | 12.30 (12.27–12.33) | 11.59 (11.57–11.60) | <.001 | 12.43 (12.41–12.46) | 11.61 (11.60–11.62) | <.001 |
 Inpatient staysb | 0.126 (0.125–0.127) | 0.099 (0.098–0.099) | <.001 | 0.121 (0.121–0.122) | 0.097 (0.096–0.097) | <.001 |
 Physician density of residenceb | 1.901 (1.897–1.904) | 1.955 (1.952–1.957) | <.001 | 1.976 (1.972–1.980) | 2.018 (2.015–2.020) | <.001 |