Table 3.
Relative contribution of changes in the gestational age distribution and in gestational age-specific SIDS rates to the overall reduction in SIDS rates by plurality and gestation, United States, 2004-05 vs. 1995–96
|
Kitagawa decomposition – traditional method (per 10,000 live births) | ||||||
|---|---|---|---|---|---|---|
| Plurality and gestational age (weeks) | Contribution of changes in gestational age distribution | Contribution of changes in gestational age-specific SIDS rate | Sum of both components (overall decline) | Relative contribution of changes in gestational age distribution (%) | Relative contribution of changes in gestational age- specific SIDS rate (%) | Sum of both components (%) |
| Singletons | ||||||
| 22-36 weeks |
+0.18 |
−0.63 |
−0.45 |
+40.0 |
−140.0 |
100 |
| ≥37 weeks |
+0.19 |
−2.46 |
−2.27 |
+8.4 |
−108.4 |
100 |
| Total |
+0.37 |
−3.09 |
−2.72 |
+13.6 |
−113.6 |
100 |
| Twins | ||||||
| 22-36 weeks |
+1.29 |
−3.09 |
−1.81 |
+71.3 |
−171.3 |
100 |
| ≥37 weeks |
−0.98 |
−0.82 |
−1.80 |
−54.3 |
−45.7 |
100 |
| Total |
+0.31 |
−3.92 |
−3.61 |
+8.6 |
−108.6 |
100 |
|
Modified Kitagawa decomposition (per 10,000 fetuses-at-risk) | ||||||
| Singletons | ||||||
| 22-36 weeks |
<0.01 |
−0.44 |
−0.44 |
<0.0 |
−100.0 |
100 |
| ≥37 weeks |
−1.22 |
−1.04 |
−2.26 |
−54.0 |
−46.0 |
100 |
| Total |
−1.22 |
−1.48 |
−2.70 |
−45.2 |
−54.8 |
100 |
| Twins | ||||||
| 22-36 weeks |
−0.35 |
−1.42 |
−1.77 |
−19.7 |
−80.3 |
100 |
| ≥37 weeks |
−1.90 |
+0.13 |
−1.77 |
−107.2 |
+7.2 |
100 |
| Total | −2.25 | −1.29 | −3.54 | −63.5 | −36.5 | 100 |
Explanatory note: Between 1995–96 and 2004–05, singletons experienced a decrease in SIDS (−2.72 SIDS per 10,000 live births; 100% decrease). Under the traditional model, changes in gestational age distribution among singletons increased SIDS rates (+0.37 cases per 10,000 live births; 13.6% increase), whereas changes in gestational age-specific SIDS rates decreased SIDS rates (−3.09 cases per 10,000 live births; 113.6% decrease)