I have a database of the volume of a certain type of test across time. I want to show how the trend in the volumes of this test have changed at a certain point - around the start of the COIVD pandemic.

Besides showing this in a graph, I was wondering if there is a statistical test i can run to show how the trend changes around that time.

Thinking of using regression with a knot around the timepoint - but I was wondering if there is something better to use.

Thank you in advance good people

Sample data below

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input int date float study
21454 1
21525 1
21335 1
21424 1
21222 1
21405 1
21265 1
21283 1
21515 1
21500 1
21399 1
21328 1
21500 1
21458 1
21234 1
21535 1
21682 1
21899 1
21911 1
21682 1
21885 1
21710 1
21871 1
21895 1
21879 1
21774 1
21860 1
21801 1
21895 1
21818 1
21868 1
22174 1
22055 1
22050 1
22117 1
22141 1
22273 1
22070 1
22105 1
22105 1
22259 1
22196 1
22236 1
22001 1
22075 1
21976 1
21935 1
22271 1
22091 1
22250 1
22127 1
22251 1
21985 1
21942 1
21966 1
22494 1
22501 1
22578 1
22512 1
22445 1
22568 1
22305 1
22561 1
22371 1
22421 1
22589 1
22399 1
22460 1
22476 1
22314 1
22592 1
22404 1
22434 1
22582 1
22561 1
22390 1
22307 1
22462 1
22637 1
22419 1
22452 1
22453 1
22587 1
22368 1
22385 1
22579 1
22606 1
22419 1
22307 1
22351 1
22413 1
22295 1
22481 1
22319 1
22490 1
22725 1
22726 1
22768 1
22652 1
22880 1
end
format %td date