How to Calculating time difference between visits in a panel data

[humphrey Kimani Wanjiku]

I hope this finds you well.

I kindly need your help to calculate the time difference(Months, Years or Day) in a longitudinal data set where I have patients with recorded visits up to 8 visit. Some patients have up to 3rd visit, 5 visit.. etc. I have date of each visit and I would like to get the time difference between each visit for each patient.

Regards

Humphrey

[Andrew Musau]

You need to provide some example data consisting of the patient identifier and time variable. Assuming that these are named patient_id and date in your data set, you can copy and paste the result of the following:

ssc install dataex
sort patient_id date
dataex patient_id date in 1/10

[humphrey Kimani Wanjiku]

input uniqueidentifier(Patient ID) , DateTested , Visit_order
1 20508 1
1 20508 2
2 20457 1
2 20545 2
3 20456 1
3 20458 2
4 20460 1
4 20468 2
5 20464 1
5 20464 2
6 20879 1
6 21243 2
7 20908 1
7 21135 2
8 20502 1
8 20968 2
9 20746 1
9 20891 2
10 20746 1
10 20891 2
end
format %tdD_m_Y DateTested
[/CODE]

[Andrew Musau]

Thanks for the data example.

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(Patient_ID DateTested Visit_order)
 1 20508 1
 1 20508 2
 2 20457 1
 2 20545 2
 3 20456 1
 3 20458 2
 4 20460 1
 4 20468 2
 5 20464 1
 5 20464 2
 6 20879 1
 6 21243 2
 7 20908 1
 7 21135 2
 8 20502 1
 8 20968 2
 9 20746 1
 9 20891 2
10 20746 1
10 20891 2
end
format %tdD_m_Y DateTested

bys Patient_ID (DateTested): gen time_lapse= DateTested- DateTested[_n-1] if _n>1

Note that the time lapse will be in days.


Result:

. l, sepby(Patient_ID)

     +--------------------------------------------+
     | Patien~D   DateTes~d   Visit_~r   time_l~e |
     |--------------------------------------------|
  1. |        1   24 Feb 16          1          . |
  2. |        1   24 Feb 16          2          0 |
     |--------------------------------------------|
  3. |        2   04 Jan 16          1          . |
  4. |        2   01 Apr 16          2         88 |
     |--------------------------------------------|
  5. |        3   03 Jan 16          1          . |
  6. |        3   05 Jan 16          2          2 |
     |--------------------------------------------|
  7. |        4   07 Jan 16          1          . |
  8. |        4   15 Jan 16          2          8 |
     |--------------------------------------------|
  9. |        5   11 Jan 16          1          . |
 10. |        5   11 Jan 16          2          0 |
     |--------------------------------------------|
 11. |        6   01 Mar 17          1          . |
 12. |        6   28 Feb 18          2        364 |
     |--------------------------------------------|
 13. |        7   30 Mar 17          1          . |
 14. |        7   12 Nov 17          2        227 |
     |--------------------------------------------|
 15. |        8   18 Feb 16          1          . |
 16. |        8   29 May 17          2        466 |
     |--------------------------------------------|
 17. |        9   19 Oct 16          1          . |
 18. |        9   13 Mar 17          2        145 |
     |--------------------------------------------|
 19. |       10   19 Oct 16          1          . |
 20. |       10   13 Mar 17          2        145 |
     +--------------------------------------------+

[humphrey Kimani Wanjiku]

It worked.
Thank you very much