st: issues with tsset based on more than a time variable and duplicates conflicting results

["Abdalla, Ahmed" <ahmed.abdalla@kcl.ac.uk>]

Dear Statalist
I want to tsset my data based on  permno yr mth:
I tried - tsset permno yr mth  - I get the error message "too many varaibles specified"
I tried - gen firmid= group(permno)
              gen timeid = ym(yr, mth)
               tsset firmid timeid  - I get the error " repeated time values with panel
So I tried to investigate my duplicates :
I run the command:
duplicates report firmid timeid
I get
   copies | observations       surplus
----------+---------------------------
        1 |      2181223             0
        2 |        53712         26856
        3 |        16515         11010
        4 |         9556          7167
        5 |         5510          4408
        6 |         1698          1415
        7 |          196           168
        8 |           48            42
        9 |           18            16

I drop my duplicates and tsset my data, it works properly. But I though to investigate the duplicates again and run this code (of course before dropping my duplicates):
duplicates report permno mth yr, I get:

   copies | observations       surplus
----------+---------------------------
        1 |      2268476             0


Why both duplicates drop based on firmid and timeid versus permno yr mth are different though the firm id groups permno and the timeid groups yr and mth ?
Is there any other way to tsset my data based on permno yr mth rather than the grouping I have done (firmid and timeid) ?


Thanks

  
 
 
 
     
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