I am not part of unipark.
According to the pdf-manual from 2016 (yeah, quite a bit outdated but cant find anything about this in the online manual) its NOT. Page 280, headline 6.2.2 clearly says “Bitte beachten Sie: Es handelt sich um eine Zufallsauswahl, nicht um eine Gleichverteilung.” – roughly translated as “Please note: This is a random selection, not an uniform distribution”
I would suggest using a user defined variable filled by a random trigger (execution position: direct, execute trigger in preview: yes, execute trigger multiple times: no, values from 1 to 4). Then you have to create four filters using the user defined variable and adding a page to each filter. A random trigger has to option to aim for uniform distribution. But it is unlikely that you’ll get exactly 250 participants for each bucket. You could end up with something like 248/249/253/250.
Why? Lets assume we have just two buckets and want three participants per bucket. From what I know the number is added to the bucket when the participant finishes the questionnaire. Two people start the questionnaire and both get the number “1” from the random trigger (random number generator or rng). Another two people start the questionnaire and get “2” from rng. None of those four has finished the questionnaire and now three participants entering the questionnaire. So the rng could assign them 1/1/2 and if all 7 participants finish the questionnaire, you’ll end up with 4/3. But it could also happend that one of those with the number “2” doesnt finish the questionnaire and you’ll have 4/2 at the end.
Also have a look at
checking the last paragraph “Uniform distribution”.
Would be great for you (and me) if Unipark could confirm that.