Adjusted logistic model on frequency of twinning in different postal code areas of South Hesse (20 425 mothers, 275 mothers of twins)
| n | df | p | Odds ratio | 95% CI | ||
|---|---|---|---|---|---|---|
| Lower | Upper | |||||
| Postal code area | 4 | 0.042 | ||||
| PCA (5+6) | 5316 | reference | ||||
| PCA (1) | 3892 | 1 | 0.005 | 1.889 | 1.208 | 2.953 |
| PCA (2) | 6627 | 1 | 0.003 | 2.032 | 1.282 | 3.220 |
| PCA (3) | 1200 | 1 | 0.011 | 1.767 | 1.141 | 2.737 |
| PCA (4) | 3390 | 1 | 0.101 | 1.689 | 0.902 | 3.162 |
| Mother’s age (years) | 20425 | 1 | 0.007 | 1.037 | 1.010 | 1.065 |
| Parity | 2 | 0.033 | ||||
| Nulliparae | 9933 | reference | ||||
| Primiparae | 7358 | 1 | 0.065 | 0.778 | 0.595 | 1.016 |
| Multiparae | 3134 | 1 | 0.019 | 0.621 | 0.417 | 0.926 |
| Nationality | ||||||
| German | 15299 | reference | ||||
| Not German | 5126 | 1 | 0.748 | 1.050 | 0.781 | 1.412 |
| Constant | 1 | 1 | 0.000 | 0.003 | ||