Using all 12 months of the 2011 basic CPS datafiles downloaded from NBER, I run a frequency of the variable PRCHLD for the population ages 16 to 24 and get 3,666,839.
Using all 12 months of the 2011 basic CPS datafiles from IPUMS, I run a frequency of the variable NCHILD for the population ages 16 to 24 and get 2,863,036.
Incidentally, I do get the same number of total population age 16 to 24.
I am not sure why I get different frequencies, and think that it must have something to do with the variable construction. Any thoughts? Thank you!
The NBER CPS variable PRCHLD indicates the age group of own children in the household. Instead, you should calculate the frequency for number of own children using the variable PRNMCHLD. Then you should compare this frequency to the IPUMS-CPS variable NCHILD.
Note that PRNMCHLD will still differ from NCHILD. While PRNMCHLD is self-reported and only counts unmarried children 18 or younger, NCHILD is constructed by IPUMS using the Family Interrelationship logic and has no age/marital status restrictions on identifying children. If you prefer to use the PRNMCHLD variable, then you can link your IPUMS data extract to its matching NBER basic monthly file using the IPUMS variables HRHHID, HRHHID2, LINENO, SEX, RACE, and AGE (with corresponding NBER variables) to identify unique CPS respondents.
Hope this helps.