I am trying to compare different variables for different observations within a group - and I am not sure if this is even possible in Stata.

I would like to count the number of alive siblings alive at age 5 (or alternatively the age of the death) of the observed child.

From the data, I have been able to generate the first four columns, but need to construct a column along the lines of column 5 here.

HH Child Age at Survey Age at Death Number of siblings alive at age 5(/at age of death)
1 1 18 4 1
1 2 15 - 1
1 3 11 - 2
1 4 8 - 2
2 1 4
...

Can anyone help?