Exclude participants from previous studies filter not working

“Exclude participants from previous studies” filter not working? I already submitted a help request but was wondering if anyone else has noticed this recently. Details: I have an ongoing study over zoom. I run a prescreen study every week or two and recruit batches of participants. In the most recent prescreen, 5 (out of 30) participants had already completed the prescreen in the past despite the filter. I just launched another prescreen and again I see at least one repeat participant.

EDIT: There was a question in the prolific participant redit about this—seems like participants have noticed repeat studies as well.

Thank you David

This is important. Have you posted a support request?

In other words, please may I confirm, the custom blacklist, in a duplicated study or added by yourself manually, was there but participants whose ID were in the custom blacklist were allowed to take the survey?

The custom blacklist will be generated if a study is duplicated via the duplicate study option in the Action menu on the study page.

If so, or in any event, I think we need the help of @Jon on this one m(._.)m

Having a look on Reddit I see that there is a thread from a year ago

but not more recently.


I duplicated my prescreen and checked that the previous studies were in there (though I didn’t check every single one, just eyeballed to see that the filter was behaving as it has in the past).

This reddit thread is from three days ago: https://www.reddit.com/r/ProlificAc/comments/uzioxv/studies_i_have_done_in_the_past_are_showing_up_on/?utm_source=share&utm_medium=web2x&context=3

Can’t help but wonder if it has anything to do with “empting the queue” from a few days ago:

Dear David

Thank you very much indeed. @Jon I think this is urgent!


I think our engineering team would agree with you @timtak! They’re on the case already, so I’ll follow along and relay any further updates when I know more.

In the mean time, it’s probably best to assume the Exclude Participants from Previous Study feature is out of service for the moment - either in being entirely unavailable or not returning desired results if you are seeing it in your app. You should still be able to build a custom blocklist to exclude previous study participants, albeit in a bit more labour-intensive way.

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I’ve had the same problem, 6 participants from a previous study have been able to return and start the study again. No new data was collected, because they were blocked in Qualtrics, but they still marked the survey as completed with NOCODE.

What should I do? I don’t want to have to pay these participants again for no contribution, and if I reject their work, they will get marked down for a mistake by Prolific.

It’s much worse than I thought, at least 40 participants were allowed to start the survey and Qualtrics did not block all of them. I will therefore have to delete all their data.

Can someone please advise on how I should proceed in terms of approving or rejecting participants that completed the same survey TWICE because Prolific’s filter was not working properly? That’s a lot of money wasted and lost data that I cannot afford.

Sorry to hear about that @Leo_C, I appreciate the annoyance and extra hassle on this one! Rest assured though a fix is hopefully not far off :crossed_fingers:

Our support team can help you with rejecting the duplicate participants from your study in a way that won’t penalise them for their double participation. To do so, raise a support ticket and share the study IDs of your current study with the duplicate entries and the previous one you had attempted to duplicate from. If you can share the participant IDs you’ve so far identified as duplicate as well, that’ll help greatly.

Updating on this, our engineers have released a fix for the blocklist issue, so the exclude participants from previous studies feature should begin to start excluding participants from previous studies again.

NB on my use of “should” above - if your study is live and a participant who should be excluded already has access to it, this fix will not automatically remove them from the study.

For new studies, this feature is now switched back on, so you should now again be able to exclude previous participants with a few clicks (though worth doublechecking, just in case!)

Apologies again for the inconvenience this caused, hopefully though it should be back up and trouble free from now on.

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Do other researchers know of this issue? Will there be any communication of this issue? I only knew about repeat participants because I message participants to invite them to the full study and I can see our message history.

Our Support team is leading on getting the message out, so hopefully all who are affected should be notified in due course (if not already). My understanding is it’s a relatively small number of studies who had experienced this issue.

Generally speaking when there’s a major outage, planned downtime, or otherwise, we’ll get the message out via email, on Twitter, and here in the community as well.


I’m still having problems with the exclude list function. I just released a new study, excluding the previous version in the criteria, and just noticed that 11 out of 20 participants actually took part in the previous version. Is it possible to be refunded for this if the exclusion feature is not working properly? I can’t use the repeat data in my analysis.



Dear Agnes

Welcome back.

I am sorry to hear that. I have no idea how that could have happened. When something goes wrong like that I guess that the only way forward is to contact support. I hope they give you are refund since it sounds like something went wrong with the system.


I am having the same problem too.

I created a preliminary study and then duplicated it (because I want to increase the payment a little) before increasing the number of places and there is no exclude list

  1. neither in the Participation on Prolific screener section (participation in prior studies) as I think it should be,
  2. nor in the Custom Block list (with the list of IDs) which I think would be strange anyway.

I also can not add to the duplicate my own prescreener
3) Participation on Prolific screener section (participation in prior studies - the preliminary)
4) A custom block list (“must be Prolific IDs” message. I have had this before and I forget how I solved it)

I think that (2) is irrelevant and (4) because I am doing something wrong (perhaps the coding of the characters or spaces, or perhaps one of the Prolific IDs is incorrect).

But with regard to (1) The lack of the prior study being blocked in the duplicate and (3) my inability to select the prior study to be blocked in the duplicate, I think that this may be because the prior preliminary study is still “Active” (because one of the participants failed all three attendance
checks on a 2 minute study and I am asking that participant to return their submission before attempting to reject them. It is an insignificant amount of money but I wanted their to be a moral hazard, or maybe I am just a curmudgeon).

Does anyone know if my presumption is correct: Duplicates of Active studies do NOT contain re-participation prevention?

I see that when it comes to representative samples it is necessary to Manually select either
Exclude participants with a block list
Exclude participants from previous studies

I am not sure whether it is now necessary to do this manually on NON representative samples but these buttons are not displayed and in the past duplicates automatically included a re-participant block.


Aha. The wayward participant kindly returned their submission so as soon as the last submission is complete, and they a little while longer, the study will be complete and I will be able to test the hypothesis.

But I can’t wait so I just increased places on the preliminary study, which means it will be a while before I can complete a study.