xtreg y x1 x2 i.year, fe
When variables are highly persistent over time, lagged levels make weak instruments for first-differenced equations. System GMM fixes this by estimating a system of two equations: one in differences (instrumented by lagged levels) and one in levels (instrumented by lagged differences).
* Running a regression with a lagged independent variable xtreg investment L.capital market_value, fe Use code with caution. 2. Exploring Panel Topology: xtsum , xttab , and xtline
* Run RE with cluster-robust standard errors quietly xtreg leverage size profitability tangibility, re cluster(firm_id) xtoverid Use code with caution. A significant stata panel data exclusive
I can provide the exact, production-ready Stata code block for your model. Share public link
xtreg y x1 x2 if group == 1, fe xtreg y x1 x2 if group == 2, fe Use code with caution. Copied to clipboard 4. Critical Diagnostic Tests
Before diving into estimation, Stata offers specialized tools for understanding your panel data structure: xtreg y x1 x2 i
This will estimate a random-effects model of y on x1 and x2 .
If your dataset contains a variable id for subjects and year for time, type: xtset id year Use code with caution.
This clean, production-ready script synthesizes the entire workflow discussed above into a repeatable template for your empirical research. Share public link xtreg y x1 x2 if
where panelvar is the variable that identifies the panel units (e.g., individual ID) and timevar is the variable that identifies the time periods.
xtoverid // after RE estimation (requires ivreg2)
qui xtreg y x1 x2, fe xttest3
After running a model, you must check for common panel‑data violations: heteroskedasticity, autocorrelation, and cross‑sectional dependence.
Note: Time-invariant variables (e.g., gender, country) are dropped in FE models. B. Random Effects (RE) Model