I have noticed a big discrepancy( which only increased post covid) in the fertility rate and births reported when compraring the ACS data with the CDC data, 3.6M births in cdc and 4M in the acs for 2023 for example.
Why is the difference so big? It certainly cannot be justified solely based on the acs being for the mid point of the year and so for births for 2022M7 to 2023M6. Even adjusting for the possibility of some women who had a birth in the last 12M having had the baby outside the US the difference is still too big
Thanks in advance
A couple of thoughts
You need to give a specific reference for where you got your numbers. Are you looking at data.census.gov ? If so, what table ID and what geography?
The ACS data is based on self report
In the PAST 12 MONTHS, has this person given birth to any children?
ACS data tables only report age as "Under 5 years" (tables) and "0" less than 1 year in PUMS so you wouldn't be able to figure out if a person was born in a particular based on a table or pums data.
The children may not live with the mother and wouldn't be included in the ACS household count data.
Based on a google search 3.1% of the us population are from a multiple birth. Assuming that you are only looking at twins, this results in a 3.1% increase of the CDC numbers over the count of recent mothers in the ACS question.
The CDC data is based on the
https://www.cdc.gov/nchs/products/databriefs/db507.htm
What count do you get when you analyze this file ?
The CDC uses data from the natality data file from the National Vital Statistics System. The vital statistics natality file is based on information from birth certificates and includes information for all births occurring in the United States. This Data Brief accompanies the release of the 2023 natality public-use file (2)
ftp.cdc.gov/.../Nat2023us.zip
In any case, please provide a reference for your numbers.
Thanks
Dave
For the 3.6 Million it is from the cdc wonder: https://wonder.cdc.gov/controller/datarequest/D149
The 4 Million is from the ACS with the Person weight: https://data.census.gov/app/mdat/ACSPUMS1Y2023/table?cv=FER(1,2)&wt=PWGTP
From what you say the CDC wonder should have 3.1% more births than the ACS but that is not the case.
Will this eventually be corrected so the difference is not so big?
A couple of comments. The PUMS query FER variable is the ACS checkoff "have you given birth within the last 12 months." So it needs the "twins" correction. I emailed the people at the NCHS. There is a recent publication with fertility stats for 2023. https://www.cdc.gov/nchs/data/nvsr/nvsr74/nvsr74-1.pdf It has some comments and a reference comparing the birth certificate (CDC/NCHS data) and the ACS. The reference is "unpublished" so hopefully they will send the reference. Here is a crosstab for a single PUMA where I live. Infant is the PUMS variable AGEP<=1. Birth is the FER variable:
InfantFertility None One Twins Birth 111 844 87 No 28836 1100 50 NA 79844 5891 338
Twins in 2+ persons in household with age <=1. Triplicates + is pretty smaill. The table is counts of individuals
The ACS is combined with CDC data to get variables that do not appear on the birth certificate which contains mother's & father's age sex of baby race & education of parents : US Standard birth certificate: https://www.cdc.gov/nchs/data/dvs/birth11-03final-acc.pdf Most states use the US standard birth certificate or something similar but some states may not.