MLP Linkage File Does Not Work Out of the Box When Linking to 1940


I am a “new” user of the MLP linkage infrastructure MLP Linked Data and using the free script that IPUMS provides for linking Decennials:

For linking 1920 to 1940, the script does not work on my Mac machine. On the line:

quietly joinby histid_year_b' using "path’/extract_2'_to_merge.dta", unmatched(both) _merge(link_year_a’_`year_b’)

I get the error:

variable histid_1940 not found

I haven’t seen much on Census linkages in the forum so I thought I would document this. The error appears to be in the creation of the linkage file:


which is in fact missing the hist_1940 variable.

I’m sorry that you’re having issues with this do-file. In order to avoid issues like this in the future and make the MLP linkage process easier, IPUMS USA will soon be integrating the MLP links into the core extract system. The release of this feature has been delayed but is likely to be ready next spring.

In the meantime, I suggest coding the process yourself as described on the MLP User Guide. The included do-file just implements this procedure in a flexible way that can be easily adapted for any combination of samples. However, the flexibility increases the complexity, which means troubleshooting issues with that file can be difficult.