Modifying HITs

Once a HIT has been created in the Amazon Mechanical Turk (Mechanical Turk) marketplace, it's possible to modify it; however, there is an important caveat. Because your HIT is now available to workers, Mechanical Turk will not allow you to make changes that will negatively impact them. For example, Mechanical Turk won't let you delete a HIT on which a worker is actively working. The following are the common operations you can perform to modify HITs.

Modify expiration time

When a HIT is created, the LifetimeInSeconds is used to calculate an ExpiresAt value that tells Mechanical Turk when to remove a HIT from the marketplace if it hasn't been completed yet. You can use the UpdateExpirationForHIT operation to either extend this time further into the future to allow workers more time to complete it or shorten the time if responses are no longer valuable.

A common use of UpdateExpirationForHIT is to call it with a value of 0 or a time in the past to tell Mechanical Turk to immediately expire a HIT. This is useful when you make a mistake in your HIT definition and immediately need to remove the task from the marketplace. Note that this won't prevent workers who have already accepted your HIT from completing and submitting it.

Add additional assignments

When a HIT is created, the MaxAssignments value is provided and informs Mechanical Turk of how many workers can submit responses for the task. If you need to allow additional workers to provide responses, you can call CreateAdditionalAssignmentsForHIT to add additional available assignments.

A common pattern for managing quality in Mechanical Turk is to ask multiple workers to provide responses for a given task and then compare the results. One approach for doing this is to start with a minimal number of assignments and then add additional assignments if there is disagreement among workers. You can use this approach to limit the number of assignments needed for tasks where there is general agreement, while gathering additional data points for tasks that are more ambiguous.

Note that HITs created with fewer than 10 assignments cannot be extended to have 10 or more assignments.

Modify the HIT Type

The HIT Type attributes of a HIT, such as the reward amount, title, or assignment duration, can be modified by changing the HIT Type assigned using the UpdateHITTypeOfHIT operation. While this can allow you to modify any of the HIT Type attribute values on an active HIT, Mechanical Turk prevents you from changing the HIT Type on HITs with assignments that have been accepted or submitted by workers.

Delete

The DeleteHIT operation disposes of HITs that are no longer needed. Calling this operation deletes your HIT from Mechanical Turk. Once deleted, it is no longer available if you call ListHITs, GetHIT, or ListAssignmentsForHIT. HITs must be in a Reviewable state to be disposed and all of the completed assignments must be either approved or rejected. As a result, this operation isn't a solution for removing HITs that you published by mistake, you should instead use the UpdateExpirationForHIT operation to immediately expire your task. HITs are automatically disposed after 120 days.