Table 2.
Multivariable analysis
| Low-volume vs mid-volume | High-volume vs mid-volume | |||
|---|---|---|---|---|
| Characteristic | aOR (95% CI) | P-value | aOR (95% CI) | P-value |
| Age (year) | ||||
| <37 | 1.00 (reference) | 1.00 (reference) | ||
| ≥37 | 0.92 (0.87–0.98) | 0.008 | 0.96 (0.92–1.01) | 0.150 |
| Primary payer | ||||
| Private | 1.00 (reference) | 1.00 (reference) | ||
| Self | 1.04 (0.97–1.11) | 0.277 | 1.00 (0.94–1.06) | 0.920 |
| Other | 1.10 (1.00–1.20) | 0.051 | 1.01 (0.93–1.09) | 0.786 |
| Unknown | 0.85 (0.73–0.99) | 0.049 | 0.81 (0.71–0.91) | <0.001 |
| Household income | ||||
| QT1 (lowest) | 0.99 (0.88–1.11) | 0.831 | 1.16 (1.05–1.27) | 0.004 |
| QT2 | 1.03 (0.93–1.15) | 0.527 | 1.14 (1.04–1.24) | 0.004 |
| QT3 | 0.96 (0.89–1.04) | 0.327 | 0.98 (0.91–1.05) | 0.615 |
| QT4 (highest) | 1.00 (reference) | 1.00 (reference) | ||
| Unknown | 0.96 (0.64–1.43) | 0.832 | 0.96 (0.67–1.37) | 0.817 |
| Patient location | ||||
| Large central metropolitan | 1.00 (reference) | 1.00 (reference) | ||
| Large fringe metropolitan | 1.02 (0.94–1.10) | 0.714 | 1.07 (1.00–1.14) | 0.064 |
| Medium metropolitan | 0.98 (0.88–1.09) | 0.695 | 1.01 (0.92–1.12) | 0.773 |
| Small metropolitan | 1.04 (0.90–1.20) | 0.604 | 0.99 (0.87–1.13) | 0.879 |
| Micropolitan | 0.82 (0.68–0.99) | 0.035 | 0.84 (0.71–0.99) | 0.040 |
| Not metropolitan/micropolitan | 1.13 (0.90–1.41) | 0.287 | 1.02 (0.83–1.25) | 0.884 |
| Unknown | 1.20 (0.71–2.04) | 0.497 | 1.43 (0.90–2.27) | 0.128 |
| Infertility | ||||
| No | 1.00 (reference) | 1.00 (reference) | ||
| Yes | 0.91 (0.85–0.97) | 0.003 | 0.98 (0.92–1.03) | 0.384 |
| Charlson comorbidity | ||||
| 0 | 1.00 (reference) | 1.00 (reference) | ||
| ≥1 | 0.83 (0.69–0.98) | 0.029 | 0.91 (0.78–1.06) | 0.224 |
| Polycystic ovary syndrome | ||||
| No | 1.00 (reference) | 1.00 (reference) | ||
| Yes | 1.12 (0.92–1.38) | 0.265 | 1.14 (0.94–1.38) | 0.179 |
| Region | ||||
| Northeast | 0.73 (0.67–0.79) | <0.001 | 1.12 (1.05–1.20) | 0.001 |
| Midwest | 0.97 (0.88–1.06) | 0.501 | 0.83 (0.76–0.90) | <0.001 |
| South | 0.89 (0.79–1.01) | 0.062 | 0.87 (0.78–0.96) | 0.009 |
| West | 1.00 (reference) | 1.00 (reference) | ||
| Hosp teaching | ||||
| Urban non-teaching | 1.00 (reference) | 1.00 (reference) | ||
| Urban teaching | 0.91 (0.60–1.38) | 0.659 | 1.63 (1.08–2.46) | 0.020 |
| Hosp bed capacity | ||||
| Small | 1.00 (reference) | 1.00 (reference) | ||
| Mid | 1.51 (1.05–2.17) | 0.026 | 1.18 (0.86–1.61) | 0.315 |
| Large | 1.19 (0.84–1.68) | 0.329 | 1.03 (0.76–1.39) | 0.856 |
A multinomial regression model for multivariable analysis. Mid-volume months (2nd/3rd quartiles) served as the referent group. aOR adjusted-odds ratio, CI confidence interval, QT quartile