TY  - RPRT
        AU  - Lechner, Michael
AU  - Rodríguez-Planas, Núria
AU  - Fernández-Kranz, Daniel
        TI  - Difference?in?Difference Estimation by FE and OLS when there is Panel Non?Response
        PY  - 2015/Nov/
        PB  - Institute of Labor Economics (IZA)
        CY  - Bonn
        T2  - IZA Discussion Paper
        IS  - 9490
        UR  - https://www.iza.org/publications/dp9490
        AB  - We show that the OLS and fixed-effects (FE) estimators of the popular difference-in-differences model may deviate when there is time varying panel non-response. If such non-response does not affect the common-trend assumption, then OLS and FE are consistent, but OLS is more precise. However, if non-response is affecting the common-trend assumption, then FE estimation may still be consistent, while OLS will be inconsistent. We provide simulation as well as empirical evidence for this phenomenon to occur. We conclude that in case of unbalanced panels, deviating OLS and FE estimates should be considered as evidence that non-response is not ignorable for the differences-in-differences estimation.
        KW  - attrition
KW  - difference-in-difference estimation
KW  - balanced panel
KW  - panel estimation
KW  - unbalanced panel
        ER  -