I am working with survey data. Respondents are given the option to respond in different units for some questions. For example, take weight: respondents may choose to either respond in kgs, or lbs. Thus, I have two separate variables that measure the same concept (i.e. variable 1 is weight_kgs, and variable 2 is weight_lbs), but each unique ID will have an observation either recorded in kgs, or in lbs.

After converting the observations to the same unit (i.e. both will be in kgs), I would like to create one variable that contains both the observations originally recorded as kgs (weight_kgs), as well as those just converted from lbs.

I tried to merge the variables, but that did not work. Any way to do this on Stata?