I am using ACS 2021 1-year file on the SDA tool. When I cross CBHHTYPE (Census bureau household type (with cohabiting)) with YNGCH (Age of youngest own child in household) and filter for PERNUM = 1, I see a small number of cases where the respondent’s youngest child is under 18 (YNGCH < 18) but the value for CBHHTYPE is 4 (Cohabiting couple household, NO own children <18) or 7 (Female householder, no spouse/partner present, with relatives, NO own children) or 11 (Male householder, no spouse/partner present, with relatives, NO own children <18).
The example below uses PERWT but the results are similar using HHWT.
Unlike CBHHTYPE, which is provided by the Census Bureau, YNGCH is created using IPUMS family interrelationship links in MOMLOC and POPLOC. These links are not reported in the original data but are constructed by IPUMS based on a protocol that uses information from other variables and contextual information to determine probable family relationships; notably, they identify a householder and their unmarried partner as a couple and therefore both as parents to children assigned to either the householder or their partner via the protocol. The majority of cases where CBHHTYPE is inconsistent with YNGCH is with CBHHTYPE = 4 (Cohabiting couple household, NO own children <18), which makes sense given that the ACS definition of an own child does not explicitly include the child of an unmarried cohabiting partner whereas the IPUMS protocol is to link such cases.
Thank you, @Ivan_Strahof, for the explanation. It is very helpful.