Table 4. Mixed effects spline regression models (risk ratio with 95% confidence interval) for severe morbidity and failure to rescue.
| Severe Morbidity Model | Failure to Rescue model | |
|---|---|---|
| Annualized delivery volume | See figure 1-a | See figure 1-b |
| Age | ||
| <20 | 0.98 (0.96-0.99) | 0.81 (0.67-0.99) |
| 20-24 | 1.00 (Referent) | |
| 25-29 | 1.14 (1.13-1.16) | 1.15 (1.02-1.29)) |
| 30-34 | 1.32 (1.30-1.33) | 1.34 (1.19-1.52) |
| ≥35 | 0.89 (0.88-0.90) | 1.75 (1.55-1.98) |
| Year | ||
| 1998 | 1.00 (Referent) | 1.00 (Referent) |
| 1999 | 1.05 (1.02-1.07) | 1.36 (1.06-1.73) |
| 2000 | 1.02 (0.99-1.05) | 1.16 (0.89-1.50) |
| 2001 | 1.06 (1.04-1.09) | 1.07 (0.82-1.40) |
| 2002 | 1.11 (1.08-1.14) | 1.09 (0.85-1.40) |
| 2003 | 1.11 (1.08-1.14) | 0.91 (0.71-1.18) |
| 2004 | 1.13 (1.10-1.16) | 0.79 (0.61-1.01) |
| 2005 | 1.11 (1.08-1.14) | 0.93 (0.72-1.20) |
| 2006 | 1.19 (1.16-1.22) | 0.58 (0.44-0.76) |
| 2007 | 1.14 (1.12-1.17) | 0.57 (0.43-0.74) |
| 2008 | 1.33 (1.29-1.36) | 0.73 (0.56-0.94) |
| 2009 | 1.32 (1.29-1.36) | 0.81 (0.63-1.05) |
| 2010 | 1.28 (1.25-1.32) | 0.81 (0.63-1.05) |
| Household income | ||
| Lowest quartile | 1.00 (Referent) | 1.00 (Referent) |
| Second quartile | 1.02 (1.01-1.03) | 1.21 (1.08-1.36) |
| Third quartile | 1.00 (0.99-1.01) | 0.93 (0.81-1.06) |
| Highest quartile | 0.96 (0.95-0.97) | 0.89 (0.77-1.04) |
| Unknown | 1.02 (0.99-1.05) | 1.08 (0.79-1.47) |
| Insurance status | ||
| Medicare | 1.62 (1.56-1.68) | 1.20 (0.83-1.72) |
| Medicaid | 1.17 (1.16-1.18) | 1.34 (1.21-1.47) |
| Private | 1.00 (Referent) | 1.00 (Referent) |
| Self pay | 1.09 (1.07-1.12) | 1.43 (1.17-1.73) |
| Other | 1.20 (1.17-1.22) | 1.48 (1.19-1.85) |
| Unknown | 1.22 (1.13-1.32) | 0.78 (0.31-1.96) |
| Race | ||
| White | 1.00 (Referent) | 1.00 (Referent) |
| Black | 1.19 (1.18-1.21) | 1.77 (1.56-2.00) |
| Hispanic | 0.90 (0.88-0.91) | 1.34 (1.17-1.54) |
| Other/unknown | 1.15 (1.13-1.16) | 1.10 (0.96-1.27) |
| Hospital bed size | ||
| Small (<400) | 1.00 (Referent) | 1.00 (Referent) |
| Medium (400-600) | 1.03 (1.00-1.07) | 1.25 (0.89-1.76) |
| Large (>600) | 1.14 (1.10-1.18) | 1.66 (1.15-2.39) |
| Hospital Location | ||
| Rural | 1.00 (Referent) | 1.00 (Referent) |
| Urban | 1.08 (1.03-1.13) | 1.11 (0.65-1.90) |
| Hospital Region | ||
| Northeast | 1.00 (Referent) | 1.00 (Referent) |
| Midwest | 0.88 (0.80-0.96) | 0.79 (0.37-1.72) |
| South | 1.23 (1.12-1.35) | 2.18 (1.03-4.58) |
| West | 1.01 (0.91-1.11) | 2.19 (1.01-4.77) |
| Hospital Teaching | ||
| Non-teaching | 1.00 (Referent) | 1.00 (Referent) |
| Teaching | 0.96 (0.92-0.99) | 0.99 (0.67-1.46) |
| Unknown | 0.90 (0.86-0.95) | 2.18 (1.40-3.39) |
| Hospital Owner | ||
| Government | 1.00 (Referent) | |
| Private non-profit | 1.03 (0.98-1.08) | 1.00 (Referent) 0.58 (0.34-0.98) |
| Private investor | 0.95 (0.89-1.01) | 0.71 (0.39-1.31) |
| Unknown/other | 1.17 (1.11-1.24) | 1.11 (0.60-2.04) |
| Comorbidity Index | 1.56 (1.56-1.56) | 1.07 (1.05-1.09) |
For severe morbidity, annualized delivery volume was modeled based on a 5-piece restricted cubic spline transformation with knot locations at 377, 1252, 2170, 3437, and 7163. For failure to rescue annualized delivery volume was modeled based on a 5-piece restricted cubic spline transformation with knot locations at 432, 1478, 2378, 3600, and 7433.