Duplicate participant: What happened?

My Prolific study redirects to Qualtrics. In my Qualtrics data, the same Prolific ID appears twice, with the same Session ID, but that Prolific ID only appears once on my list in Prolific. Furthermore, each person with this Prolific ID completed the study during overlapping times, beginning a few minutes apart, on machines with different screen resolutions. They reported similar background data but different ages. Only one of them matches the Prolific demographics for this Prolific ID?

Does anyone have any idea what happened here? How could two different people have the same Prolific ID and Session ID? Why doesn’t the Prolific ID show up twice in my Prolific list?

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Hey @Brad_Hoot, hope you’ve been well!

Our system is set up such that each participant can have only one submission per study on Prolific. That is, each participant will be listed in your dashboard only once, and can only be paid once.

However, we can’t prevent people from visiting the survey link more than once after they have opened it for the first time. Sometimes, participants revisit a survey link if, for example, they have missed the completion URL. It is important to distinguish between submissions on Prolific (which we guarantee are unique) and submissions to your survey software such as Qualtrics (which we don’t have control over).

To prevent duplicate entries in Qualtrics, or other survey software, enable the “Prevent Ballot Box Stuffing” option, or similar.

If a participant takes your study twice (for whichever reason), then we recommend that you simply delete the second submission from your data set (by checking their participant ID) and judge whether to approve or reject them based on the first submission alone.

I hope this helps! Let me know if you have any other questions :slight_smile:

Thanks for the reply, @Josh! I do understand that Prolific obviously doesn’t control what happens on Qualtrics, and that someone could reload the Qualtrics page or something. What I found odd was that the two completion times overlapped and also had different screen resolutions (which is captured in this Qualtrics study. So it looks like someone used the same Prolific ID to complete the study simultaneously on two different devices, maybe? The two attempts provided coherent (although slightly different) demographic data, so I don’t think it was someone just “clicking through” and imputting nonsense, which you might expect if they were doing the task on two screens at the same time in an attempt to get paid twice, perhaps not understanding how Prolific works.

I guess I’m just trying to figure out what happened so that I can get a sense of whether I should delete both submissions from my data set (I already approved the first, presumably legitimate one on Prolific, assuming that the person at least completed the study once, whether fully cooperatively or not). If this person wasn’t really doing the study in good faith because they were just using two devices to click through without paying much attention, then I’d rather just remove them, which is why I’m trying to figure out what happened.

Any thoughts about what these facts might indicate? I know Prolific keeps each ID unique and can’t control Qualtrics, but I don’t know if I’m taking into account everything that could account for what happened here. Thanks!

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That’s a good point, and you’re right, it does look suspicious.

Could you message the participant to see if they have a valid explanation for what occurred? If they do not, you can get help from our support team, who will investigate the account :slight_smile:

OK, maybe I’ll reach out to the participant, thanks!

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