I want to use maternal age distribution by race and by year to predict number of children with Down syndrome born (absent terminations), as there is a direct link between maternal age and chance on a child with DS. I would think that the age distribution of mothers with children of 0 year of age in 1970, gives an indication of maternal age distribution at birth in 1970; age distribution of mother of children of 1 year of age in 1970 would then yield maternal age distribution (at birth) in 1969; 2 yrs of age for 1968, etc. However, maternal age distribution in the USA census IPUM-data constructed in this way does not match the information in the USA natality files. Well it does more or less for 1970 and 1969 (but seems to be shifted 1.5 years), but start to be reaaly different if you go down to 1968, 1967,…1961. Why? Is it a result of recoding ages for privacy reasons? Cause if that is so, I just should not use the IPUM data for this topic.
So, the question to IPUM is: has there been such a recoding of age that maternal age distribution are not very precise?