What miss option means in gunique ?

[Lucrecia Lei]

Deat Stata user,
I found this gunique function, and using the same variable list I got different total observations and unique observations by adding or not add

miss

option.

gunique id name_first name_last
N = 19,632,203; 4,678,062 unbalanced groups of sizes 1 to 6,026

gunique id name_first name_last, miss
N = 19,632,557; 4,678,416 unbalanced groups of sizes 1 to 6,026

Does anyone knows why the N and number of unbalanced groups are different in these 2 cases? And what means size 1 to 6026?

Thanks a lot!

[Clyde Schechter]

When you specify the -miss- option, -gunique- includes missing values as distinct values; without that option -gunique- skips over observations with missing values. So that's why with -miss- you get a bigger total N and a larger number of groups. The sizes refer to how many observations are associated with a given distinct value. So, in your case, there is some combination of id, name_first, and name_list that appears only once in the data set. And there is some combination that appears 6,026 times. All other combinations appear some number of times between those limits.

[Lucrecia Lei]

When you specify the -miss- option, -gunique- includes missing values as distinct values; without that option -gunique- skips over observations with missing values. So that's why with -miss- you get a bigger total N and a larger number of groups. The sizes refer to how many observations are associated with a given distinct value. So, in your case, there is some combination of id, name_first, and name_list that appears only once in the data set. And there is some combination that appears 6,026 times. All other combinations appear some number of times between those limits.

Hi Clyde, Thank you so much!