st: Is demeaning variables that cover different time periods, but are used in the same regression, a problem?

[Bertel Teilfeldt Hansen <geilfeldt@gmail.com>]

Dear statalisters!

I am currently writing a thesis about countries' level of democracy
and their economic growth, where democracy is operationalized as a
stock-variable (something that accumulates over time). To eliminate
time-invariant and unit-specific errors I wish to employ country-fixed
effects (time-demean the variables in my regression).

Here's the problem, though: For theoretical reasons, I would like to
demean each country's stock of democracy from 1800 till 2009, whereas
I - because of scarcity of data - can only demean other variables from
1960 till 2009. This means that I want to include a variable that has
been demeaned with regards to a long period of time, and other
variables that have been demeaned with regards to a shorter period of
time in the same regression.

Now, this is no problem to do technically, but what I'm unsure of is
how big of a statistical problem it is. I have a hunch that it is
somewhat of a problem, but how grave it is, I really don't know.

Kind regards

- Bertel Teilfeldt Hansen, University of Copenhagen
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