Sudden infant death syndrome: a re-examination of temporal trends

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)

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