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The March CPS has two person ID variables. Which one should a user interested in merging husbands with wives or parents with children use?
The relevant variables from the March 1998 CPS are described below:
|PH-SEQ||Household seq number||2||5||00001:99999|
Trailer portion of unique household
|A-PARENT||Parent’s line number||2||11||00:39|
|A-SPOUSE||Spouse’s line number||2||18||00:39|
Expanded relationship code
01 Reference person with relatives
02 Reference person without relatives
05 Own child
10 Other relative
11 Foster child
12 Nonrelative with relatives
14 Nonrelative without relatives
1 Married – civilian spouse present
2 Married – AF spouse present
3 Married – Spouse absent
7 Never married
The following are selected person records from the March 1998 CPS. It is clear that parent’s line number (A-PARENT) and spouse’s line number (A-SPOUSE) are referring to line number (A-LINENO) rather than the trailer portion of the unique household ID (PPPOS).
For the most part, the difference between A-LINENO and PPPOS is "40." However, one should not create a new variable:
PERSONID = PPPOS – 40;
This is because, on occasion, the difference between A-LINENO and PPPOS is not "40." See the following records from these data:
An explanation for the difference between PPPOS and A-LINENO is provided by Greg Weyland of the Census Bureau:
In many cases it is true that a person's line number and their PPPOS value are identical, but they are not always so. This is because these variables come from different sources and have somewhat different uses. The PPPOS variable is only found on the March files. It is a strict count of the number of person records within a household and is assigned in an order consistent with a certain predetermined structure of the household. A-LINENO, on the other hand, is a variable that appears on all CPS files. It is a number that is consistent with the household roster of individuals provided at the time of interview. It does not change throughout a household's time in the CPS sample.
For example, a household may have 5 individuals listed on the roster at the time of the first interview. These individuals would have line numbers of 1-5 assigned to them. If say line number 3 moves out after the second month interview, Line numbers 4 and 5 retain their values and the household will appear on CPS files without a line number 3. For the same household, if March occurred during the first month interview, PPPOS 1-5 would be used. If, however, the March interview occurred in the third month interview, only PPPOS values of 1-4 would be found for the household. Moves into and out of the household can also cause the PPPOS values to be assigned in a manner that is not consistent with the order of line numbers in a household.