Table 4. Average and summary ASD PAFs for PTB, SGA, and CD.

Risk factor(s)	1994 Birth cohort		2000 Birth cohort		Change in PAF (95% CL*)
	No. of cases	Average PAF, % (95% CL*)	No. of cases	Average PAFs, % (95% CL*)
PTB	703	4.2 (0.0† to 8.7)‡	1339	2.0 (0.0 to 4.0)
SGA	703	0.9 (0.0 to 3.5)‡	1339	3.1 (1.0 to 5.0)
CD	703	7.9 (6.2 to 9.5)‡	1339	6.7 (3.0 to 10.0)
PTB or SGA or CD (summary measure)	703	13.0 (7.7 to 19.5)	1339	11.8 (7.5 to 15.9)	1.2 (−9.3 to 5.4)
Subgroup analyses: summary PAFs
ASD with ID	234	12.3 (1.8 to 23.0)	377	17.1 (8.5 to 25.9)	4.8 −9.1 to 18.6)
ASD without ID	305	9.6 (0.8 to 18.6)	680	12.2 (6.2 to 18.5)	2.6 −8.3 to 13.1)
ASD, ID Unknown	164	20.5 (9.0 to 31.7)	282	3.4 (0.0 to 12.7)	−17.1 (−31.3 to −2.3)
Males	580	13.6 (6.9 to 20.2)	1116	10.8 (6.2 to 15.4)	−2.8 (−11.2 to 4.8)
Females	123	10.2 (0.0 to 24.8)	223	16.3 (6.1 to 26.8)	6.1 (−12.0 to 24.3)

^*Bootstrap CLs based on 1000 replications. A 95% CL was estimated as the 2.5 and 97.5 percentiles of the 1000 replica estimates; each resampled data set comprised case-control sets from the original study sample randomly selected with replacement.

^†For average PAF estimates, lower bound of CL is reported as 0.0 for all instances in which lower bound estimate was <0.0.

^‡Bootstrap CL could not be directly estimated due to small sample sizes. A hybrid method was used in which information gleaned from the 2000 birth cohort variance estimation was applied to the 1994 cohort data.