Once you have your web experiment up and running at a public URL, you'll enter your study URL into Prolific for distribution to participants. Prolific will send out your study URL to the requested number of participants who meet your pre-screening criteria.
Using Qualtrics as an example, your web experiment may have a URL that looks like this:
https://northwestern.az1.qualtrics.com/jfe/form/SV_37ZsJox1kU5FypE
Log in to Prolific, select your study or create a new study. Scroll down to the "What is the URL of study" text input field and enter your study URL.
Next, select "I'll use URL parameters". Notice the additional text that's now appended to the study URL.
When a participant clicks on your web study link, the {{%PROLIFIC_PID%}} portion will be replaced with the participant's unique Prolific ID. Each participant will effectively be clicking on a URL that is unique to them.
On the receiving end, Qualtrics is able to read and store the URL parameters from each participant. The stored responses are now linked to to a specific participant. While this isn't typically needed for analysis purposes, it is often times useful when resolving technical problems or to help determine if a specific participant has (or has not ) fully completed the study.
The same concept of capturing the participant's ID URL parameter applies to other study platforms such as PCIBex or if you're building your own experiment platform with VueJS and Firebase.
While the variable name "PROLIFIC_PID" is automatically inserted by Prolific, it is arbitrary and could be manually replaced with some other label. You may use any other variable name but generally speaking, URL parameters work best with letters and numbers. Avoid using spaces and punctuations in your variable names.
| variable name |
acceptable? |
| pid |
yes |
| participantID |
yes |
| participantId |
yes |
| participant_id |
yes |
| participant ID |
no (contains spaces) |
| participant.id |
no (contains punctuation) |
| PROLIFIC_PID |
yes |
| prolific_pid |
yes |
| prolific PID |
no (contains spaces) |