Dear all experts,

I try to calculate the average of some variables for each observation.
My code is:

Code:
egen laporta_ave = mean(con_of_corr rul_of_law reg_qua gov_eff poli_stab voice_acc), by(obsnum) /*The "by(obsnum)" option tells Stata to calculate the average for each observation.*/
I am sure the variables in the mean() exist in my daatset. I am wondering why they turn out :


Code:
.                  egen laporta_ave = mean(con_of_corr rul_of_law reg_qua gov_eff poli_stab voice_acc), by(obsnum) /*The "by(obsnum)" option tells Stata to calculate the average for each observation.*/
con_of_corrrul_of_lawreg_quagov_effpoli_stabvoice_acc invalid name
r(198);
Thank you so much and best regards