Mechanical Turk Concepts
This section describes the concepts and terminology that you must understand to use Amazon Mechanical Turk effectively.
A Requester creates tasks on Mechanical Turk for Workers to work on. As a Requester, you use the Requester User Interface (RUI) to create tasks, check the status of your tasks, and accept or reject work performed on tasks. Workers see your account name (specified by your Amazon.com account) when they view and accept your tasks.
Human Intelligence Tasks (HITs)
A Human Intelligence Task (HIT) is a single, self-contained task a Requester creates on Mechanical Turk, for example, "Identify the color of the car in the photo."
You can assign many Workers to work on the same HIT, which is useful way of getting consensus on a subject by many workers giving the same answer. A Worker can only accept a HIT once and can only submit one assignment per HIT. This guarantees that multiple Workers must complete a HIT that has multiple assignments.
If a Worker fails to complete an assignment before the time frame specified (i.e., the Worker abandons the HIT), or if the Worker chooses not to complete it after accepting it (i.e., the Worker returns the HIT), the assignment becomes available for other Workers to work on.
A Worker is a person who completes assignments. Workers use the Mechanical Turk website (http://mturk.amazon.com/) to find assignments to work on, submit responses, and manage their account.
Master Workers are Workers who have demonstrated the ability to provide successful results for specific types of tasks across multiple Requesters on the Mechanical Turk Marketplace. Mechanical Turk offers Master Workers in Photo Moderation and Categorization, but you can ask them to do any type of HIT.
Approval and Payment
Workers submit responses for assignments. If you approve their work, Mechanical Turk transfers the HIT reward from your Mechanical Turk account to their Amazon Payments accounts. Workers don't get paid if you reject their work.
When you post a batch of HITs, you agree to approve or reject work by a specified deadline. If that deadline passes, Mechanical Turk approves the assignments and pays the Workers who submitted work.
Amazon Mechanical Turk processes payment of the reward to the Worker after you approve the assignment. Amazon Mechanical Turk transfers the reward from your Amazon.com account to the Worker's Amazon.com account. Before you can post your batch of HITs, you must have enough money in your account to pay for all of the work. You can deposit or withdraw funds from your Mechanical Turk account at any time using the Requester website (http://requester.mturk.amazon.com/).
It is important to note that anyone can register to work in the Mechanical Turk Marketplace. To control who can work on your HITs, you can require that Workers have specific “Qualifications” before they can work on your HITs. You can create your own custom Qualification Types and assign them to Workers. Or, you can use the Qualification Types provided by Mechanical Turk.
Mechanical Turk provides several Qualification Types including Approval Rate, which is the percentage of assignments submitted that have been approved, and Assignments Approved, which is the number of Assignments that were approved for the Worker. The Approval Rate and Assignments Approve Qualification Types are automatically calculated based on a Worker's account statistics and history. If you don't want to use Workers who just registered this morning and have no work history, we recommend that you require Workers to have a 95% Approval Rate and 1,000 Approved Assignments to work on your project.
The Master Qualification Types give you easy access to Master Workers who have demonstrated the ability to provide successful results for specific types of tasks across multiple Requesters on the Mechanical Turk Marketplace. Mechanical Turk offers Master Workers in Photo Moderation and Categorization, but you can ask them to do any type of HIT.