Unique Turker is a service that allows requesters on Amazon Mechanical Turk to limit the number of times that a single worker may work on a group of HITs. This service may be useful for:
The preferred way to ensure unique workers is with Qualifications. Compared to other solutions, Qualifications create a better experience for workers and is more robust (harder for workers to circumvent).
Instructions are provided here: https://myleott.com/uniqueturker_via_quals.pdf
Use the form to the right to generate a custom script that you can copy and paste into the HTML of one or more of your HITs. The script will enforce a "Max # HITs / worker" constraint across all HITs where it appears.
Note: Be sure to use the same "unique identifier" across your multiple HITs. Scripts with different identifiers will use different databases.
Not sure where to paste the script? Try clicking "Edit HTML" in the "Design Layout" section of your HIT. Then, paste the script at the top of your HIT's HTML.
Limitations: Some workers are able to circumvent this script, so please double check submissions for duplicate Worker IDs.