Understanding HIT Types

In many common uses of Amazon Mechanical Turk, you will want to ask many questions of the same kind, such as identifying an object in each of thousands of photos. A single Worker can answer one or many of these questions. To make it easy for Workers to find your HITs, Amazon Mechanical Turk groups similar HITs together, and Workers search and browse the groups. If a Worker qualifies for HITs in the group, the Worker may preview a single HIT, then accept it and begin work. When a Worker completes one HIT in a group, Amazon Mechanical Turk shows the Worker another HIT from the same group. Most Workers will complete many similar HITs in a single session.

Amazon Mechanical Turk groups HITs together based on their HIT type. A HIT type is defined by the values for a set of common properties. Two HITs with identical values for these properties are considered to be of the same HIT type, and appear in the same group on the Amazon Mechanical Turk website.

Your application can use HIT types to manage different kinds of work. Each HIT type has a HIT type ID, which your application can use to query for HITs of a particular type. The HIT type ID may also be used with the CreateHITOperation operation in place of the common property values, to ensure that the new HIT will be assigned the same type as other HITs.

Note

HITs, Hit types, and Qualifications types are available until they are explicitly disposed (using either the DisposeHIT or DisposeQualificationType operations), or until they have been inactive for 120 days. HITs and their related assignment data are disposed 120 days after you approve or reject the assignments. HIT types and Qualification types are disposed 120 days after their last use. If you require access to HIT data for longer than 120 days, we recommend you keep a local copy.

The HIT properties that define a HIT type are the following:

You can explicitly register a new HIT type by calling RegisterHITType. This operation takes values for the common parameters, and returns a HIT type ID for the type that matches the values. You can create HITs using the new type by calling the CreateHITOperation operation with the type ID, and values for the properties specific to the HIT (such as the Question).

You can create a HIT without specifying a HIT type ID by passing values for the common parameters directly to the call to CreateHITOperation . If the values match an existing HIT type, the HIT will be given the existing type. If the values do not match an existing HIT type, a new type is created with those values. In either case, the HIT type ID is returned with the HIT data in the response from the call to CreateHITOperation .

	Tip
	To avoid accidentally passing mismatched values for two HITs that ought to be part of the same type, register the HIT type using RegisterHITType, then create the HITs using the HIT type ID.

Once you have created a HIT, you might want to change the HIT type. Use the ChangeHITTypeOfHITOperation operation to do this.

HITs of the same HIT type can have differing values for the following properties: