Table 2.
Characteristics of the study cohort by volume category after removal of excluded data
| All n (%) | Volume category (cases/year within time period [TP])
|
|||||||
|---|---|---|---|---|---|---|---|---|
| Small (10–99) n (%) | Medium (100–199) n (%) | Large (> 200) n (%) | ||||||
| Center × TPs | 158 | (100) | 40 | (25.3) | 72 | (45.6) | 46 | (29.1) |
| Operations | 85,023 | (100) | 7,162 | (8.4) | 33,740 | (39.7) | 44,121 | (51.9) |
| Females | 39,197 | (46.1) | 3,331 | (46.5)a,b | 15,571 | (46.1)a,c | 20,295 | (46.0)b,c |
| Males | 45,826 | (53.9) | 3,831 | (53.5)a,b | 18,169 | (53.9)a,c | 23,826 | (54.0)b,c |
| Neonates | 14,986 | (17.6) | 1,121 | (15.7) | 5,894 | (17.5)c | 7,971 | (18.1)c |
| Infants | 28,783 | (33.9) | 2,285 | (31.9)a | 11,111 | (32.9)a | 15,387 | (34.9) |
| Children | 41,254 | (48.5) | 3,756 | (52.4) | 16,735 | (49.6) | 20,763 | (47.1) |
| Risk category | ||||||||
| 1 | 17,935 | (21.1) | 1,822 | (25.4) | 7,592 | (22.5) | 8,521 | (19.3) |
| 2 | 28,389 | (33.4) | 2,488 | (34.7)a,b | 11,322 | (33.6)a,c | 14,579 | (33.0)b,c |
| 3 | 29,434 | (34.6) | 2,246 | (31.4) | 11,505 | (34.1) | 15,683 | (35.5) |
| 4 | 6,563 | (7.7) | 480 | (6.7)a | 2,442 | (7.2)a | 3,641 | (8.3) |
| 5&6 | 2,702 | (3.2) | 126 | (1.8) | 879 | (2.6) | 1,697 | (3.8) |
| Outcome | ||||||||
| Discharge | 79,786 | (93.8) | 6,717 | (93.8) | 31,398 | (93.1) | 41,671 | (94.4) |
| Death | 5,237 | (6.2) | 445 | (6.2) | 2,342 | (6.9) | 2,450 | (5.6) |
The proportion of each variable differs significantly (Bonferroni-corrected p < 0.002) between volume categories except as indicated
a
No difference between small and medium centers
b
No difference between small and large centers
c
No difference between medium and large centers