Generate an indicator for number of observations by dyad with multiple imputated panel data

[Matthew Campbell]

Dear Statalist,
I would have a basic question and came to no clue after intensive search over the web.

I am using a panel dataset with repeated observations for individuals (and dyads) over several waves. However, I have used multiple imputation (10 imputations) and I cannot create a variable that counts for how many waves the dyads are in the dataset. Obviously, since I have repeated measurements for each of the 10 imputed dataset, I cannot apply something like:

bys dyad: gen nyear=[_N]

Would you have any practical solutions to this problem?



Below you can find an example of my data structure ("_mi_m" is the imputation dataset number)

* Example generated by -dataex-. For more info, type help dataex
clear
input float pid byte(dyad wave _mi_m)
1 1 1  1
1 1 1  2
1 1 1  3
1 1 1  4
1 1 1  5
1 1 1  6
1 1 1  7
1 1 1  8
1 1 1  9
1 1 1 10
1 1 2  1
1 1 2  2
1 1 2  3
1 1 2  4
1 1 2  5
1 1 2  6
1 1 2  7
1 1 2  8
1 1 2  9
1 1 2 10
1 1 4  0
1 1 5  0
1 2 1  1
1 2 1  2
1 2 1  3
1 2 1  4
1 2 1  5
1 2 1  6
1 2 1  7
1 2 1  8
1 2 1  9
1 2 1 10
1 2 2  1
1 2 2  2
1 2 2  3
1 2 2  4
1 2 2  5
1 2 2  6
1 2 2  7
1 2 2  8
1 2 2  9
1 2 2 10
1 2 4  0
1 2 5  0
2 4 1  1
2 4 1  2
2 4 1  3
2 4 1  4
2 4 1  5
2 4 1  6
2 4 1  7
2 4 1  8
2 4 1  9
2 4 1 10
2 4 2  1
2 4 2  2
2 4 2  3
2 4 2  4
2 4 2  5
2 4 2  6
2 4 2  7
2 4 2  8
2 4 2  9
2 4 2 10
2 4 3  1
2 4 3  2
2 4 3  3
2 4 3  4
2 4 3  5
2 4 3  6
2 4 3  7
2 4 3  8
2 4 3  9
2 4 3 10
2 4 4  0
3 3 2  0
3 3 4  0
3 3 5  0
end

[Ali Atia]

bysort dyad (wave): egen wanted = total(wave!=wave[_n-1])

[Matthew Campbell]

Dear Ali Atia,
thank you so much for this! Your solution solved my problem... This was exactly what I was looking for.

[Nick Cox]

An alternative formulation is as the count of distinct values.

egen tag = tag(dyad wave) 
egen wanted = total(tag), by(dyad)

See https://www.stata-journal.com/articl...article=dm0042

[Matthew Campbell]

Dear Nick Cox,
many thanks for this suggestion. Yes, I also think that this formulation is more intuitive. I will check the paper you suggests ("Speaking Stata: Distinct observations") and also the distinct command.