Table 1.
Descriptive statistics of all US Medicare fee-for-service beneficiaries (n = 63,009,173) from 2000 through 2016 and in subsets of the study population including only Medicare beneficiaries with low exposure levels a,b.
| Covariate | Category | Full cohort | Low-level PM2.5 | Low-level NO2 | Low-level ozone |
|---|---|---|---|---|---|
|
|
|
|
|
||
| N (%) | N (%) | N (%) | N (%) | ||
|
| |||||
| Number of hospitalizations | CVD | 18,610,833 (29.5) | 3,755,279 (17.6) | 6,860,947 (25.1) | 8,362,303 (29.6) |
| CHD | 6,607,687 (10.5) | 1,323,950 (6.3) | 2,561,172 (9.4) | 2,914,271 (10.7) | |
| CBV | 5,551,735 (8.8) | 985,934 (4.7) | 1,933,203 (7.1) | 2,340,200 (8.7) | |
| Total person years (median per person) | CVD | 401,315,016 (5) | 99,144,014 (3) | 152,544,344 (4) | 146,294,509 (4) |
| CHD | 448,888,035 (6) | 105,830,022 (4) | 167,032,565 (5) | 158,088,646 (4) | |
| CBV | 460,574,345 (6) | 107,822,290 (4) | 171,669,892 (5) | 160,960,817 (4) | |
| Demographic characteristics at study entry | |||||
| Sex | Female | 34,725,534 (55.1) | 11,110,862 (52.1) | 14,518,670 (53.1) | 15,417,275 (54.6) |
| Age entry | 65–74 years | 48,240,802 (76.6) | 18,721,927 (87.8) | 23,089,599 (84.4) | 21,313,724 (75.5) |
| 75–84 years | 10,819,118 (17.2) | 1,850,369 (8.7) | 3,085,751 (11.3) | 4,877,852 (17.3) | |
| 85 + years | 3,949,253 (6.3) | 740,483 (3.5) | 1,183,791 (4.3) | 2,043,443 (7.2) | |
| Race | White | 53,262,938 (84.5) | 18,252,212 (85.6) | 24,220,341 (88.5) | 23,265,492 (82.4) |
| Black | 5,511,612 (8.7) | 1,290,529 (6.1) | 1,849,345 (6.8) | 2,696,881 (9.6) | |
| Other/unknown | 4,234,623 (6.7) | 1,770,038 (8.3) | 1,289,455 (4.7) | 2,272,646 (8.0) | |
| Medicaid eligibility | Not eligible | 55,164,043 (87.5) | 19,003,470 (89.2) | 24,236,200 (88.6) | 24,551,536 (87.0) |
| Eligible | 7,845,130 (12.5) | 2,309,309 (10.8) | 3,122,941 (11.4) | 3,683,483 (13.0) | |
| Region | Midwest | 15,254,270 (24.2) | 3,444,574 (16.1) | 6,238,743 (22.8) | 10,118,066 (35.8) |
| Northeast | 13,880,261 (22.0) | 4,461,736 (20.9) | 3,539,969 (12.9) | 8,319,138 (29.5) | |
| Southeast | 17,454,647 (27.7) | 5,406,735 (25.4) | 10,923,504 (39.9) | 4,437,350 (15.7) | |
| Southwest | 6,616,448 (10.5) | 2,566,482 (12.0) | 3,428,315 (12.5) | 1,625,681 (5.8) | |
| West | 9,803,547 (15.6) | 5,433,252 (25.5) | 3,228,610 (11.8) | 3,734,784 (13.2) | |
For PM2.5, Medicare beneficiaries with exposure levels always below 10 μg/m3 PM2.5 were included (for CVD n = 21,312,779; for CHD n = 21,099,651; for CBV n = 21,045,932). For NO2, Medicare beneficiaries with exposure levels always below 20 ppb NO2 were included (for CVD n = 27,359,141; for CHD n = 27,123,026; for CBV n = 27,073,535). For ozone, Medicare beneficiaries with exposure levels always below 40 ppb ozone were included (for CVD n = 28,235,019; for CHD n = 27,220,654; for CBV n = 26,992,359).
Demographic characteristics in subsets of the study population including only Medicare beneficiaries with low exposure levels are given for the CVD subsets.