CAN I ADD A VARIABLE TO AN ALREADY DOWNLOADED DATA SET FOR STATA?

I ALREADY DOWNLOADED A CENSUS IPUMS DATA IN STATA. I HAVE STARTED CLEANING THE DATA. CAN I ADD A VARIABLE TO AN ALREADY DOWNLOADED DATA SET?

It is possible to attach new variables to an already downloaded dataset using the variables YEAR, DATANUM, SERIAL, and PERNUM to uniquely identify each record (all of these variables are automatically selected for each extract). Simply create a new extract with the variables you would like to attach to your previous extract, and then merge the two files using YEAR, DATANUM, SERIAL, and PERNUM.

I hope this helps.