Randomly assigning participants to an experimental condition for returning participants

URL of experiment: still in development

Description of the problem: I have 2 main problems
my experiment is multi steps. i will use prolific to recruit participant
using string query i plan to automatically get their prolific ID.
using their ID i want to assign them to group A and B

  1. I am not sure of to randomly assign them to:
    A will get: a control condition (meaning skip all the pretreatments)
    B will randomly assigned between 4 pretreatments.

  2. this group will enter another session and now
    group B will get: a control condition (meaning skip all the pretreatments)
    group A will randomly assigned between 4 pretreatments.

is there a way my code could check if this participant already participated in the firs test? and the swish the condition?

i have checked https://moryscarter.com/vespr/pavlovia.php
and Pavlovia by @wakecarter but this issue is still unclear to me. my JS skills are as poor as it gets.

i hope i am clear
thank you!

If you want the same participant to get different conditions in different sessions then you need to send a pre assigned participant code to my web page and then you will get a incremental value of session.

However for half of your participants to get AB and the other half get BA then you would need to use a numerical value for participant and then assign conditions based on (int(expInfo[‘participant’])+int(expInfo[‘session’]))%2

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thank you @wakecarter
ihave 2 question :slight_smile:

  1. i am not sure how exactly to use your web page in my experiment and how to sent it a pre assigned participant code. i tried reading the crib sheet several times but was still confused where should i implement it in my experiment.

  2. it is not that they will get BA in the same experiment.
    they will get B in the first entry. and when they return (with allow list in prolific) they will get A.
    i thought of assigning them to B and A according to their ID number like
    if ((int(expInfo[‘participant’]%2):
    group A
    group B

once they are selected as group B i need a code to randomly assign them to different treatment.
i notice that in your demo the group are assigned and the get to choose a treatment.
and was wondering if i could use this script to randomly assign them

what i tried changing my experiment name in the builder to a/ and your webpage still wont open.do i need to change the name in the JS file on the experiment?

Changing experiment names doesn’t sound like the right approach.

When I said AB and BA that was referring to two sessions by the same participant. If each participant only does the experiment once then you can use the participant field generated by my web app.

Please send me a PM if you’d like to hire me to sort this out for you.

Best wishes,


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its actually a great idea
ill ask my PI (its part of my Thesis and I am getting kind of lost) and PM you if it is fine with him.
thank you!

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