I’m using the ACS NCHILD and YNGCH variables to identify couples living with their own children under age 18. My understanding is that when one partner is the household head, IPUMS constructs these variables using household relationship data (RELATE). However, in cases where neither partner is the household head, are NCHILD and YNGCH constructed based on the presence of children in the couple’s subfamily? If so, is it possible that some of the children counted as “own children” could actually be grandchildren or otherwise not the biological, adopted, or stepchildren of either partner? I’m trying to confirm whether this could introduce misclassification for couples who aren’t household heads. Thanks!
IPUMS constructs indicators of the number of children (NCHILD, YNGCH and NCHLT5) linked to an individual by the following pointer variables: MOMLOC, MOMLOC2, POPLOC, and POPLOC2. These pointer variables use the values in RELATE, along with age, sex, and marital status to assign a person to their probable coresident spouse and/or parent(s). These variables apply to parents in both same-sex and different-sex couples.
The NCHILD variable reports the number of person records in a household that list a focal person’s PERNUM value as another household member’s MOMLOC or POPLOC value; YNGCH is the age of the youngest person in the household whose MOMLOC/POPLOC value indicates that the person is their probable parent. In cases of straightforward relationship pairings (e.g., householder/spouse/child; householder/parent), there is little ambiguity. However, in some cases the algorithm may identify the wrong person. The most common structure of incorrect parental linkages is for households with multiple adult children and multiple grandchildren of the householder; the grandchildren may be assigned to the incorrect adult child as their parent in a small percentage of cases. We detail our decision making process, logic edit tree and other details in our working paper on Family Interrelationship Variables.
I would recommend a read of both our Family Interrelationships User Guide and our Overview of Subfamilies and Family Interrelationships. In this linked Subfamilies documentation, there are data examples similar to your question. I find it unlikely that grandchildren or otherwise non-biological/adopted/step-children would be classified as children to household heads because their parents are not the heads. Here is some further clarification on what are and how subfamilies are classified:
What are subfamilies, and how does the IPUMS measure them?
Subfamilies are simply families that live in the household of someone else. The Census Bureau defines two main types of subfamilies. Married-couple subfamilies comprise two spouses living with or without children. Parent-child subfamilies comprise an unmarried parent living with one or more of their own, never-married children under 18 years of age. Subfamilies can be further divided into related subfamilies (whose members are related to the household head by birth, marriage, or adoption) and unrelated subfamilies (whose members are not related to the household head). Unrelated subfamilies (which used to be called secondary families) are no longer measured by the Census Bureau, but the IPUMS includes them for users’ convenience.