I would like to generate a count variable of the unique no. of individuals in the sample. Is CPSIDP the same for the same respondent appearing in two different years of the CPS october supplement data?
Is CPSIDP same for the same individual appearing in October of two different years? (October supplement of CPS)
CPSIDP is an IPUMS-CPS defined variable that uniquely identifies individuals across CPS samples. The first six digits of CPSIDP index the four-digit year and two-digit month that the household was first in the CPS. CPSIDP allows you to link a respondent appearing with a designated household roster line number (LINENO) across samples, based on the 4-8-4 rotation pattern, by assigning a unique CPSIDP value to this line number.
Technically, yes, CPSIDP should be the same for same individual appearing in October in two different years. However, we recommend that you verify CPSIDP linkages with AGE, SEX, and RACE. In some cases CPSIDP will result in erroneous links, which are due to errors in the source data. Cases with the same CPSIDP value may also have inconsistent responses across samples due to errors on the part of the respondent or in recording the response. Ultimately, it is up to you to determine the acceptability of the linkages made using CPSIDP.
More detailed information about linking households and individuals across CPS samples is available in this paper.