Hi,

I have the following dataset in a long format with 6 records per patient_id corresponding to 3 timepoints and 2 jaws:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input int patient_id byte timepoint long(jaw retainer) double irreg_index
1 1 2 1  4.2
1 1 1 2    .
1 2 2 1 1.71
1 2 1 2  .97
1 3 2 1  .58
1 3 1 2  .22
3 1 1 3 1.18
3 1 2 1 9.83
3 2 2 1  .66
3 2 1 3  .85
3 3 1 3  .51
3 3 2 1  .98
end
I would like to calculate the difference of the irreg_index variable between timepoint3-timepoint1 per jaw separately.

I have tried to reshape my data wide in order to generate the difference :

. gen id=_n

. reshape wide irreg_index ,i( id) j(timepoint)
(note: j = 1 2 3)

Data long -> wide
-----------------------------------------------------------------------------
Number of obs. 450 -> 450
Number of variables 6 -> 7
j variable (3 values) timepoint -> (dropped)
xij variables:
irreg_index -> irreg_index1 irreg_index2 irreg_index3
-----------------------------------------------------------------------------
but as the number of rows is maintained I get many empty cells and I cannot calculate the difference as further data manipulation is needed.
Any advice would be appreciated.

Thank you,

Nikos