How to calculate the overall mean of a repeated measure with different data points across participants

[Giulia Gaggioni]

How to calculate the overall mean (over all IDs) of a repeated measure (LifeQuality).
Caveat: the number of data points across ID is different (e.g.; ID 1 has 5 entries for LifeQuality; ID 2 has 3 entries for LifeQuality etc.)

clear
input byte(ID LifeQuality)
1 2
1 6
1 8
1 7
1 9
2 2
2 2
2 1
3 5
3 6
3 3
3 4
3 5
3 6
3 7
end

[Rich Goldstein]

you seem to believe that the number of measures/ID matters but you don't tell us why it matters (e.g., more measures means "more important" in some sense (or less important) or all are supposed to have the same number but there are missing values or there may be a trend and more measures means a better measure of that trend and that needs to be accounted for or ...); of course, if the number does not matter you can just use -summ- as in:

su LifeQuality