Hello! I am working with ACS data and assigning poverty percentiles based on family income in 2019. My colleague started this work, but is currently out on leave and found an error in how the 2019 FTOINC is calculated. She received this previous instruction from IPUMS staff: “If your analysis requires a consistent family income and poverty measure, you can recalculate FTOTINC by summing INCTOT within each family unit (identified by SERIAL and FAMUNIT), and then recalculating POVERTY by first converting your new family income value to 1999 dollars by multiplying it by CPI99, and then comparing it to the 1999 poverty thresholds.”
When I use the CPI99 value of .652 to convert 2019 dollars to 1999 dollars, the poverty thresholds that are computed do not perfectly match those in the 1999 poverty threshold table: https://usa.ipums.org/usa/volii/poverty.shtml (For example, a family of 5 with 3 children in 2019 has a poverty threshold of $30,510. Converted using CPI99, that threshold in 1999 should be $19,892, but the listed 1999 threshold is $19,882.)
It seems that a small number of households who are under the poverty threshold in 2019 may appear over the 1999 poverty threshold.
Do you know why this conversion error is occurring? Is there another appropriate way to calculate this?