Hi everyone. I have a question on how pooling data in stata. I am working with a repeated cross-section with observations coming from different groups of people and periods. Between subsequent periods I have treatments. Untill now I considered separately each pair of periods (1-2 2-4 4-5 5-6), thus I estimated 4 regression results. Now I would like to pool the results, that is I would like to have one unique regression outcome and not four. I have two problems. First, period 2 for example is post treatment respect period 1, but it is pre-treatment respect period 4. Second, I need to have pre and post treatment for each group. That is for example I can keep group4 in period 5 when I compare it to period 4, but not when I compare with period 6, because group4 is missing in 6. Is there any to pool data. Thanks for the attention.


periods
Group | 1 2 4 5 6 | Total
---------------+-------------------------------------------------------+----------
group 1 | 85 51 291 189 47 | 663
group 2 | 210 195 18 477 360 | 1,260
group 3 | 246 117 14 117 69 | 563
group 4 | 5 194 18 8 0 | 225
group 5 | 102 54 62 111 75 | 404
group 6 | 91 136 88 119 135 | 569
group 7 | 253 289 295 159 164 | 1,160
group 8 | 197 352 259 401 364 | 1,573
group 9 | 123 108 0 0 0 | 231
group 10 | 108 166 300 145 37 | 756
group 11 | 293 298 354 370 373 | 1,688
group 12 | 89 4 0 61 23 | 177
group 13 | 0 185 237 185 87 | 694
group 14 | 0 226 17 0 0 | 243
group 15 | 0 0 0 104 75 | 179
group 16 | 0 0 146 141 150 | 437
group 17 | 0 0 15 205 359 | 579
---------------+-------------------------------------------------------+----------