Excluding participants from active study

Hi all,

I’m running a study with two groups at the same time. We want a representative sample in both, but also we need to exclude people for the second group if they already participated in the first. I would like to run them at the same time, since we also have a follow-up after one week - but is not necessary if required for the settings.

Since combining Representative sampling and Pre-screening options (such as exclude participants from a previous study) don’t work together (and would require the study with the first group to be closed), how do I make sure people don’t participate in both groups?

Suggestions are very welcome!

Best, Winnifred

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@Community_Leaders any thoughts? :slight_smile:

Dear Winnifred

Can you do some sort of Branching in the survey such that half the participants go to one group and the other half go to the other? Qualtrics has this functionality I believe.

Other than that you could create your own representative sample using lots of studies differing by age, gender and race. That would be very time consuming though.

Also you could just tell participants that they can only take part in one of the two groups both in the description and in the first pages of the survey and ask whether they have taken a survey on XYZ recently or with XYZ questions recently, and then direct them to a page which instructs them to return their submission if they took the other study. I think (though I am not sure) that it would be permissible to reject their submission if they proceeded with the second study even though they had taken the first since this is close to rejecting someone for not responding in conformance with their prescreening information which we are allowed to do if we use exactly the same wording. Would that be fair @Josh (when you are well – Josh is feeling under the weather right now)?

I tried my best,


Thank you, Tim!
The branching is indeed a good idea (am using Qualtrics). I was worried about how to match the follow-up survey, but since the representative sampling then has already been taken care of in the first survey, I can just use the Prolific ID numbers for sending invites for the two separate follow-up surveys with the prescreening option.

Thanks for helping!
(and get well soon, Josh)