xtreg y x1 x2, fe

Random Effects assumes that individual-specific effects are uncorrelated with the regressors.

xtreg y x1 x2, re

| Command | Purpose | |---------|---------| | xtset | Declare panel structure | | xtreg, fe | Fixed effects | | xtreg, re | Random effects | | xtivreg | IV/2SLS for panels | | xtabond2 | Dynamic GMM | | reghdfe | Multi-way FE (fast) | | xtmixed | Multilevel models | | csdid | DiD with staggered treatments | | xttest3 | Groupwise heteroskedasticity | | xtserial | Serial correlation in panels |

gen L1_x = L.x
gen F1_x = F.x
gen D_x  = D.x          // first difference

These respect panel boundaries (no cross‑unit contamination) only after xtset.

While most researchers are comfortable with standard pooled OLS or basic Fixed Effects models, Stata’s true power lies in its suite of exclusive, advanced commands designed to tackle the specific complexities of panel data. "Exclusive" in this context refers to methods that move beyond the baseline to address issues like endogeneity, dynamic relationships, and complex error structures.

This piece explores the advanced toolkit available in Stata for panel data analysis, moving from robust standard errors to dynamic modeling.

| Command | Purpose | Exclusive Feature | | :--- | :--- | :--- | | xtset | Declare Panel | Enables time-series operators for panels. | | xtreg, fe | Fixed Effects | Absorbs time-invariant unobservables. | | xtreg, be | Between Effects | Uses cross-sectional variation only. | | xtabond | Dynamic Panel | GMM estimation to fix Nickell bias. | | xtpcse | Prais-Winsten | Corrects for panel-corrected standard errors (PCSE). | | xtunitroot | Stationarity | Panel-specific unit root testing. | | xtreg, re | Random Effects | GLS estimator assuming exogeneity. |