I am working on a project that is looking at migration, and one graph I’d be interested in replicating is the one here “Who’s Leaving California…” titled ‘California is losing household at all income levels.’ I’ve reached out to the authors, but haven’t heard back from them yet.
My question is this, I understand that when running an analysis looking at poverty levels, you would want to measure families. I’ve never worked with POVERTY/FAMUNIT before, so I’m wondering if there is some guidance about whether I should restrict any calculation to FAMUNIT==1, like you might do with RELATE and household weights, or if you just run an analysis and only exclude individuals not part of a family unit. Basically I’m just not sure how to properly calculate the POVERTY/FAMUNIT estimate.
Generally speaking, you can measure poverty levels on the individual, household, family, or any other level depending on which is of most interest to you. POVERTY expresses the ratio of the sum of incomes of all family members over the poverty threshold established by the Social Security Administration for the specific family size and type (see these tables for specific threshold values). For example, if a family unit consists of three people (including one related child under 18), their poverty threshold would be $23,556 in 2022. Suppose the combined incomes of all family members was $50,000. Then the value of POVERTY for each individual in that family would be $50,000/$23,556 * 100 percent, or 212. Each member of the family will have the same value for POVERTY regardless of their individual income.
While determining where an individual is relative to the poverty line requires knowledge of family size and income, this does not mean that the family must be the level of analysis used. In fact, it appears that individuals are the unit of analysis in the shared table based on the subtitle net interstate migration among adults ages 18-64. Therefore, to recreate the table, you would need to identify individuals who migrated in and out of California using MIGPLAC1 and STATEFIP and subdivide them into groups using POVERTY. In this case, no filtering by PERNUM/FAMUNIT is required; you should then weight your estimates using PERWT.
If you wanted to generate an estimate on the family level (i.e. net number of families migrating to/from California), you would restrict your analysis to one respondent in each family. Restricting to FAMUNIT = 1 does not accomplish this for two reasons. First, since FAMUNIT indicates which family within the housing unit each person belongs to, all individuals in the first family in a housing unit will have FAMUNIT = 1. Therefore, this would include all members of the first family. Second, this restriction will omit members of any second, third, or subsequent families within the same housing unit. It’s therefore necessarily to restrict the sample to one individual each with a unique combination of FAMUNIT and SERIAL (and SAMPLE if you are including multiple years in your analysis). In this case, you would also need to create a family-level migration variable. Since there is no specific weight associated with families, you will also need to decide yourself how to proceed based on the literature. According to Chapter 11 of the ACS Methodology page, the Census Bureau uses housing unit weights for family-level estimates. You can also run this analysis on the household level. However, households may contain multiple families with differing values of POVERTY. Whether to drop these secondary families and restrict the analysis to individuals with PERNUM = 1 or not is up to the individual researcher.
Thank you Ivan, I really appreciate the response! Very clear.