Table 2.
Logistic regression on birth by age, time, and nationality, females ages 15–49, Agincourt health and demographic surveillance system, South Africa
| Model M1 | Model M2 | |||||
|---|---|---|---|---|---|---|
| Odds ratio | 95 % CI | p-value | Odds ratio | 95 % CI | p-value | |
| Mother's age | ||||||
| 15–19 | 1.000 | [1.000, 1.000] | . | 1.000 | [1.000, 1.000] | . |
| 20–24 | 1.276 | [1.177, 1.384] | <0.001 | 1.173 | [1.078, 1.277] | < 0.001 |
| 25–29 | 1.317 | [1.211, 1.433] | < 0.001 | 1.189 | [1.088, 1.299] | < 0.001 |
| 30–34 | 1.228 | [1.123, 1.342] | < 0.001 | 1.128 | [1.027, 1.240] | 0.012 |
| 35–39 | 1.013 | [0.915, 1.121] | 0.809 | 0.926 | [0.831, 1.031] | 0.159 |
| 40–44 | 0.489 | [0.427, 0.562] | < 0.001 | 0.404 | [0.348, 0.469] | < 0.001 |
| 45–49 | 0.230 | [0.184, 0.286] | < 0.001 | 0.140 | [0.107, 0.183] | < 0.001 |
| Time period | ||||||
| 1993–1996 | 1.000 | [1.000, 1.000] | . | 1.000 | [1.000, 1.000] | . |
| 1997–2000 | 0.926 | [0.853, 1.005] | 0.065 | 0.961 | [0.882, 1.046] | 0.357 |
| 2001–2003 | 0.806 | [0.737, 0.882] | < 0.001 | 0.842 | [0.767, 0.924] | < 0.001 |
| 2004–2007 | 0.926 | [0.856, 1.002] | 0.056 | 0.982 | [0.904, 1.067] | 0.674 |
| 2008–2011 | 0.880 | [0.807, 0.958] | 0.003 | 1.001 | [0.914, 1.095] | 0.99 |
| 2012–2013 | 0.786 | [0.701, 0.880] | < 0.001 | 0.890 | [0.789, 1.003] | 0.056 |
| Mother's age X time period | ||||||
| 20–24 X 1997–2000 | 1.004 | [0.895, 1.126] | 0.951 | 1.006 | [0.897, 1.128] | 0.918 |
| 20–24 X 2001–2003 | 1.025 | [0.904, 1.162] | 0.704 | 1.031 | [0.909, 1.168] | 0.636 |
| 20–24 X 2004–2007 | 0.965 | [0.863, 1.078] | 0.523 | 0.982 | [0.879, 1.097] | 0.747 |
| 20–24 X 2008–2011 | 1.030 | [0.916, 1.159] | 0.62 | 1.029 | [0.915, 1.157] | 0.636 |
| 20–24 X 2012–2013 | 1.056 | [0.906, 1.230] | 0.487 | 1.056 | [0.906, 1.230] | 0.488 |
| 25–29 X 1997–2000 | 1.032 | [0.916, 1.162] | 0.604 | 1.046 | [0.929, 1.178] | 0.454 |
| 25–29 X 2001–2003 | 1.018 | [0.894, 1.160] | 0.788 | 1.036 | [0.910, 1.180] | 0.595 |
| 25–29 X 2004–2007 | 0.992 | [0.884, 1.114] | 0.893 | 1.016 | [0.906, 1.140] | 0.782 |
| 25–29 X 2008–2011 | 0.965 | [0.853, 1.092] | 0.573 | 0.983 | [0.869, 1.112] | 0.782 |
| 25–29 X 2012–2013 | 0.899 | [0.766, 1.055] | 0.193 | 0.919 | [0.783, 1.078] | 0.299 |
| 30–34 X 1997–2000 | 1.000 | [0.882, 1.135] | 0.998 | 0.998 | [0.880, 1.132] | 0.974 |
| 30–34 X 2001–2003 | 0.901 | [0.783, 1.037] | 0.147 | 0.902 | [0.784, 1.038] | 0.15 |
| 30–34 X 2004–2007 | 0.927 | [0.819, 1.050] | 0.232 | 0.940 | [0.830, 1.063] | 0.323 |
| 30–34 X 2008–2011 | 0.923 | [0.809, 1.054] | 0.238 | 0.928 | [0.813, 1.059] | 0.267 |
| 30–34 X 2012–2013 | 0.875 | [0.737, 1.039] | 0.127 | 0.877 | [0.739, 1.041] | 0.135 |
| 35–39 X 1997–2000 | 0.882 | [0.764, 1.018] | 0.087 | 0.897 | [0.777, 1.036] | 0.141 |
| 35–39 X 2001–2003 | 0.871 | [0.744, 1.020] | 0.086 | 0.891 | [0.761, 1.043] | 0.151 |
| 35–39 X 2004–2007 | 0.819 | [0.711, 0.943] | 0.005 | 0.836 | [0.726, 0.962] | 0.012 |
| 35–39 X 2008–2011 | 0.779 | [0.669, 0.908] | 0.001 | 0.795 | [0.682, 0.926] | 0.003 |
| 35–39 X 2012–2013 | 0.749 | [0.612, 0.916] | 0.005 | 0.765 | [0.626, 0.936] | 0.009 |
| 40–44 X 1997–2000 | 0.975 | [0.802, 1.185] | 0.796 | 0.983 | [0.809, 1.196] | 0.866 |
| 40–44 X 2001–2003 | 0.788 | [0.629, 0.987] | 0.038 | 0.795 | [0.635, 0.997] | 0.047 |
| 40–44 X 2004–2007 | 0.704 | [0.577, 0.858] | 0.001 | 0.732 | [0.600, 0.892] | 0.002 |
| 40–44 X 2008–2011 | 0.698 | [0.564, 0.865] | 0.001 | 0.719 | [0.580, 0.891] | 0.003 |
| 40–44 X 2012–2013 | 0.583 | [0.435, 0.781] | < 0.001 | 0.603 | [0.450, 0.808] | 0.001 |
| 45–49 X 1997–2000 | 0.658 | [0.472, 0.916] | 0.013 | 0.657 | [0.471, 0.917] | 0.013 |
| 45–49 X 2001–2003 | 0.484 | [0.324, 0.722] | < 0.001 | 0.492 | [0.329, 0.735] | 0.001 |
| 45–49 X 2004–2007 | 0.227 | [0.146, 0.352] | < 0.001 | 0.232 | [0.149, 0.361] | < 0.001 |
| 45–49 X 2008–2011 | 0.279 | [0.180, 0.432] | < 0.001 | 0.298 | [0.192, 0.461] | < 0.001 |
| 45–49 X 2012–2013 | 0.107 | [0.043, 0.266] | < 0.001 | 0.091 | [0.033, 0.250] | < 0.001 |
| Nationality | ||||||
| South African | 1.000 | [1.000, 1.000] | . | |||
| Mozambican | 1.325 | [1.229, 1.429] | < 0.001 | |||
| Mother's age X nationality | ||||||
| 20–24 X Mozambican | 1.285 | [1.191, 1.386] | < 0.001 | |||
| 25–29 X Mozambican | 1.306 | [1.207, 1.414] | < 0.001 | |||
| 30–34 X Mozambican | 1.286 | [1.182, 1.401] | < 0.001 | |||
| 35–39 X Mozambican | 1.245 | [1.130, 1.372] | < 0.001 | |||
| 40–44 X Mozambican | 1.633 | [1.430, 1.866] | < 0.001 | |||
| 45–49 X Mozambican | 3.059 | [2.360, 3.964] | < 0.001 | |||
| Time period X nationality | ||||||
| 1997–2000 X Mozambican | 0.881 | [0.812, 0.955] | 0.002 | |||
| 2001–2003 X Mozambican | 0.859 | [0.785, 0.940] | 0.001 | |||
| 2004–2007 X Mozambican | 0.806 | [0.744, 0.873] | < 0.001 | |||
| 2008–2011 X Mozambican | 0.661 | [0.606, 0.720] | < 0.001 | |||
| 2012–2013 X Mozambican | 0.673 | [0.602, 0.753] | < 0.001 | |||
| Parameter | Parameter | |||||
| σ2 female | 0.03 | 0.00003 | ||||
| ρ | 0.008 | 0.000009 | ||||
| N | 337737 | 337047 | ||||
Unit of analysis is person-year, with variables defined at the beginning of each person-year