Hi, when checking whether the coefficients of Poisson FE correspond to those of the Poisson model with unitdummies I noticed that when using the poisson command without constant only the beta_hat of regressors starting from x2 on were identical. When using global constant all estimated coefficients were identical. This script demonstrates the phenomenon of different coefficient estimates in a poisson model w/o constant for identical regressors: <hansl> open "rac3d.gdt" -q smpl 4800 --random # construction of panel matrix mTime = seq(2001,2004)' series time = ones(1200,1)**mTime matrix units = seq(1,1200)' series pid = units**ones(rows(uniq(time)),1) delete SEX AGE AGESQ LEVYPLUS FREEPOOR FREEREPA store "rac3d_Panel.gdt" open "rac3d_Panel.gdt" -q setobs pid time --panel-vars DVISITS += randgen(P,2) # Poisson w constant list X = HSCORE HOSPADMI poisson DVISITS const X -q eval $coeff[2]~$coeff[3] list X = HOSPADMI HSCORE poisson DVISITS const X -q eval $coeff[3]~$coeff[2] # Poisson w/o constant list X = HSCORE HOSPADMI poisson DVISITS X -q eval $coeff[1]~$coeff[2] list X = HOSPADMI HSCORE poisson DVISITS X -q eval $coeff[2]~$coeff[1] <hansl>