Thanks for your reply. I’m talking specifically about the longitudinally linking weights, e.g. LNKFW1MWT.
The documentation on IPUMS defines the universe for this variable “Those individuals who are eligible to link to the next month.” The vast majority (97% from 1976-present) of people who are in MIS 8 (and therefore not eligible to link to the next month due to survey design) receive a code of zero (0), rather than missing (.). If the universe statement was correct, all of these individuals would have received a missing code (.). Further, the documentation doesn’t define values of zero (0).
The remaining 3% receive a missing code. The missing codes, from looking at the data, appear to be concentrated in “unlinkable samples”, which is consistent with the statement “Users should note that availability of these variables in a given sample is contingent on the availability of the samples required to make the given type of link” from the FAQs on weighting linked samples.
Another area where the documentation could be clarified is to be clear what is meant by adjacent months (specifically calendar MONTH vs MISH). My first assumption for interpreting LNKFW1MWT was that for someone in MISH 4, this would be the weight for MISH 5. It clearly isn’t, as everyone receives a value of 0 or ., as for MISH = 8. Instead, it looks like the relevant weight for that comparison is LNKFWMIS45WT – and adding a note in the documentation might be helpful…
I think this could be further clarified by saying “two adjacent calendar months” rather than two adjacent months and being clear in the documentation about how to interpret the weight for those in MISH 4 and 8 (who are not eligible to link to the next calendar month, yet are included in the universe for this variable).
Likewise clarifying the universe statement for LNKFW1MWT to be specific to calendar month might also help: “Individuals interviewed in a calendar month that is linkable to the next calendar month.”
Also, it would be nice to have clarity on the meaning of zero.
The reason this matters to me is that I was hoping to use these weights to identify linkable samples for analysis, rather than simply to use the weights. So, having missing codes (.) identify unlinkable samples is really helpful to me and I hope you would keep this feature.
I’m a former IPUMS staffer, so I’m happy to follow up directly with Jose or others on CPS.
And thanks to the IPUMS-CPS staff … I was delighted to learn that these weight variables (hopefully) identify unlinkable samples.