Dear Stata community,

Many thanks for all your help so far. Firstly I have found these forums so useful for my work.... I hope that I can contribute eventually (but for now I am still at a novice stage).

I have long panel data for multiple participant IDs. I would like to work out the number of days (or months) between each exam date (date_exam) for each participant (id). Time Zero is the first date for each participant (id).

My data is as follows:

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Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input int(observation id) float(date_exam date_diff advanced_cuff)
 3 1 15753 0 1
 4 1 16117 . 0
 5 1 16481 . 2
 6 1 16519 . .
 7 1 16705 . 1
 8 1 17050 . 1
 9 1 17090 . .
10 1 17286 . 1
11 1 17454 . 2
12 1 17636 . 1
13 1 17825 . .
14 1 18189 . 1
15 1 18546 . 1
16 1 18910 . 2
17 1 19099 . 2
18 1 19540 . 0
19 1 19988 . 1
20 1 20849 . .
21 1 21327 . 1
22 1 21622 . 2
24 3 14321 0 1
25 3 15263 . 0
26 3 15766 . 0
27 3 16362 . 0
28 3 17100 . 0
29 3 17461 . 0
30 3 17827 . 0
31 3 18191 . 1
32 3 18968 . 1
33 3 19472 . 0
34 3 20298 . 0
35 3 20886 . 2
37 3 21142 . 2
38 3 21369 . 2
44 4 20828 0 1
45 4 21314 . 1
47 5 17023 0 1
48 5 17349 . 0
49 5 17720 . 2
50 5 18084 . 2
end
format %tdDD/NN/CCYY date_exam
I've tried searching the internet and stata youtube.... but can't find any codes/ formulas specific to my queries.

Very many thanks once again,

Best wishes,

Roshani