Recruiting participants to begin study simultaneously


I want to employ participants recruited from Prolific in an interactive situation: a pair of people will communicate with one another in real time or ‘live’, by sending messages to one another.

In order to manage this, I wish to recruit about 240 individuals to begin simultaneously so that they can be randomized into treatment groups, and then further randomized into pairs. The two individuals within a pair will interact with one another.

All these aspects of the study are already programmed in OTree, but I don’t understand how to use Prolific to have them begin all together.

Dear Savreen

Welcome to the forum :slight_smile:
Sorry to be slow.

The most relevant FAQ on this issue is probably this

I think it is going to be very difficult to run all off your 120 pairs at the same time, but rather you are going to have to set up a few time slots and invite participants to say at which ones they are available. To do this you may wish to use


You may wish to prescreen (which will cost you) for those that are available at the time slots or just keep increasing time slots until all your pairs

Please see also the search results for Calendly here for issues that others have had with scheduling live studies


Yamaguchi University

I will echo timtak’s comment that as far as I can think of, there’s no way to ensure people are interacting at the same time unless you have people schedule times in the future. So maybe 100 sign up up on 4/1 and indicate time slots, and then your system randomly assigns people that match on time availability and sends follow-up messages with the required information for how they enter the chat space (I assume you don’t mean using the Prolific chat). For this, you’d probably pay them some small amount for the original sign-up, and then pay the full study fee at the time that they finish their interactive chat. (I guess in theory you could also try to only get people who are all available at the same time so you can manage the randomization in real time at that time, but I can imagine that’s a lot more expensive since you’d have to pay for the screening and probably only a minority of the respondents would be available for the study.)

The one caution I should give is that the problem with this is that people may not show up for the later time slot. A system that sends them a reminder (and, perhaps, also reminds them of the expected compensation) leading up to their scheduled time slot might be helpful.

Hi Savreen,

in addition to what others have suggested, I think perhaps the best option is to match participants into pairs based on their time of arrival in the study. See here: Advanced Grouping — An introduction to oTree

(Note that in this case not all participants have to start at the same time, but only 2 participants in close temporal proximity (depending on how long the participants should wait for a match)).

If participants only need to be matched once, this is likely to be successful because in my experience there is usually at least one other person who is currently participating in the study. The only case where this could become problematic is towards the end of the study (when almost all the slots are filled), because then only a few new participants are joining and thus finding a “free” partner becomes difficult.