Frederick strongly believes that the tax system in the U. S. needs to be reformed; he chose to join a local Tea Party group so they could protest a county tax increase. Frederick has type of incentive for joining this specific interest group.

Purposive

Explanation:

  A purposive incentive is one of the type of incentive that is join specifically for the group interest and the principle.

The main purpose of the purposive incentive is that it dos not provide any type of personal benefit as it serving a main cause and also the principle.

According to the given question, Frederick has the purposive incentive type that helps him to choose the specific party group on the basis of specific interest.

  Therefore, Purposive incentive is the correct answer.