Question

Only one participant can access my survey at a time, despite hundreds of available Prolific slots: possibly caused by my Randomizer configuration (?)
My survey uses a Randomizer question to draw 10 tickets per interview from an urn with 10 categories (each containing 3 items, so 30 items total). I have set the drawing type to 'Gleichverteilte Ziehung' (equal distribution, drawing without replacement), since it is essential for my study design that every participant receives exactly 10 distinct scenarios and that the distribution stays balanced across conditions.

Since launching my study on Prolific, I have received multiple reports from participants stating that they cannot access the survey, with the page indicating the study is full or unavailable — even though hundreds of places remain open on Prolific. When I checked, it appeared as though only one participant could access the survey at any given time, with others being blocked until the first participant's session had finished or advanced.

I suspect this may be related to how the Randomizer handles simultaneous draws when using the 'Gleichverteilte Ziehung' or 'Systematische Ziehung' modes, since these require the system to track what has already been drawn across all currently active interviews in order to maintain equal distribution. I assume this may create a bottleneck or locking mechanism when many participants try to access the survey and draw tickets at the same time.

Since drawing with replacement is not an option for my design (each scenario must be presented exactly once per participant), I would like to ask:

1. Is it correct that the equal-distribution or systematic drawing modes require serialized access when multiple participants draw simultaneously?
2. If so, is there a way to configure the Randomizer (e.g., a different drawing mode, or a server-side setting) that would allow multiple participants to access the survey and draw tickets concurrently, without compromising the requirement that each participant receives 10 distinct, non-repeating scenarios?
3. Alternatively, is there a known issue or limitation regarding concurrent access to surveys using this Randomizer configuration, and if so, is there a recommended workaround?

My study has already collected data, so I would prefer not to change the ticket-to-code assignment, but a change in the drawing mode itself (not the codes) should, to my understanding, not affect data comparability. I would appreciate your assessment of whether such a change is advisable given my ongoing data collection.

Thank you very much for your help.

Answer 1

Only one participant can access my survey at a time, despite hundreds of available Prolific slots: possibly caused by my Randomizer configuration (?)

Probably the issue is caused by a different problem. Most likely a participatio code or anything that is interpreted as such.

1) How does "inaccessible" look like? Can you ask a respondent for the exact wording? Maybe even for a screenshot? What you write looks like a message from Prolific, not from SoSci Survey.

2) What is the URL you gave to Prolific?

3) Have you set anything in the project settings -> specials -> variables in the questionnaire link

To answer your questions:

Is it correct that the equal-distribution or systematic drawing modes require serialized access when multiple participants draw simultaneously?

No, that is not correct. But the same value may be drawn simutaneusly, causing more respondents in one group, which SoSci Survey counter-weights in subsequent interviews.

Alternatively, is there a known issue or limitation regarding concurrent access to surveys using this Randomizer configuration, and if so, is there a recommended workaround?

No, there is no limitation, unless you explicitly add one via PHP code. Therefore, I assume that the issue lies somewhere else.

Comments

Thank you for your answer!
The URL given in Prolific is:https://www.soscisurvey.de/badetrauma2026/
There are no variables in the questionnaire link set.

Unfortunately, participants only wrote "it is throwing error/inaccessible"

Thank you for your help!

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When you open the URL a few times in different browser tabs, each should be a separate interview (unless you explicitly enabled the cookie feature in the privacy settings). You can do so to test whether concurrent interviews work correctly. I just startet 3 cases and saw no error messages.

Sometimes it also occurs that www.soscisurvey.de is unavailable for a few minuted due to system maintenance. However, that is usually only few minutes and only in the evening hours.

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Ah, yes it's the same for me. So I conclude this issue shoud lie on Prolifics side.
Thank you for checking and your help!