It can be very expensive to develop a test to measure these kinds of characteristics. For this reason alone, many employers purchase exiting tests from a variety of sources. There are literally hundreds of published tests from which to choose and some of the more useful tests cost as little as $1 per applicant. Anyone interested in selecting attest for use in personnel selection can begin with the Mental Measurement Yearbook, which summarizes many of the tests and includes a brief evaluation of their effectiveness.