# Number of observations in different panel data regressions

Given a balanced two-period panel data, with lets say 1000 observations on 500 individuals.

When you estimate a pooled OLS regression and first-differences regression is there a standard in the economics literature on how you should report number of observations.

It seems most natural for me to report 500 observations in the case of first-differences.

This might seem trivial. But better follow any standard if it exists.

• I don't see how this could be reported as anything other than 500 observations. If you ran a fixed effects regression it would be 1,000 observations but would also have 500 more parameters. – BKay Mar 9 '17 at 16:33

There is the row Observations, and the row Countries. The latter is the unit of analysis. As the data is a longitudinal panel, there are multiple observations per country. As the panel is unbalanced, the number of observations is generally not a multiple of the number of countries (e.g. for Pooled OLS (column 1), $945/150=6.3$).