Youssef , A. H., M. R. Abonazel, and E. G. Ahmed. “Robust M Estimation for Poisson Panel Data Model With Fixed Effects: Method, Algorithm, Simulation, and Application”. Statistics, Optimization & Information Computing, Vol. 12, no. 5, June 2024, pp. 1292-05, doi:10.19139/soic-2310-5070-1996.