Occasionally the results from one of the test cannot be used, either because they were somehow rendered in valid during the administration or because a special handicap of the subject made the administration of that test inadvisable altogether. In such cases, the sun of the scaled scores must of that be prorated to obtain a Verbal or Performance Score the can be used in deriving an IQ. If it is one of the Verbal test that has been omitted, the sum of the scaled scores for the five other Verbal test is multiplied by six fifths (6/5) to yield the Verbal Score. If a Performance test has been omitted, the sun of the scaled scores for the four remaining Performance test is multiplied by five fourths (5/4) to determine the Performance Score. It is possible to prorate four Verbal test by multiplying the sum of their scaled scores by 3/2, and to prorate three Performance test by the factor of 5/3, but this is inadvisable.