Mr. X's Working Memory Index (WMI) is interpretable; the components do not vary significantly, so his WMI score can be interpreted as a single construct. WMI includes three tasks. The first task, Arithmetic, consists of arithmetic problems to be solved without a pencil or paper. The second task, Digit Span, consists of repeating a string of numbers back to the examiner. The third task, Letter-Number Sequencing, consists of repeating a string of numbers and letters back to the examiner in alphanumeric order. Mr. X's WMI score of 133 (99th percentile and in the Very Superior range) may be due to many factors. He was calm, and displayed good attention and concentration throughout the tasks. He reportedly likes math and considers himself good at math. He worked a great deal with number sequences and numeric calculations during his [various jobs]. Mr. X also displayed excellent strategizing on the Digit Span and Letter-Number Sequencing tasks. Because they were not timed, he took a long time before answering each trial. During the time, he would whisper the numbers and/or letters to himself several times, usually chunking them into pairs. In Letter-Number Sequencing, he would memorize the entire string, and then whisper the string quietly to himself several times, each time vocalizing loudly to the examiner the next number or letter in the sequence.
Mr. X's Processing Speed Index (PSI) score of 122 (93rd percentile, Superior) is not interpretable, because his scores on the component tasks varied significantly. The Processing Speed Index is comprised of three tasks-Digit-Symbol Coding, in which one must match symbols to numbers using a key, Symbol Search, in which one must decide whether at least one of a pair of symbols is present in an adjacent 5-symbol set, and Cancellation, in which one must visually scan rows of symbols and identify target symbols. Mr. X's performance on these three tasks differed significantly. He achieved a scaled score of 16 on Digit-Symbol Coding (97.7th percentile or Very Superior) and Cancellation, but a scaled score of 12 on Symbol Search (75th percentile or High Average).
Mr. X exhibited a significant strength-he obtained a scaled score of 19 on the Vocabulary task, which is a non-timed subtest in which individuals are asked for the definition of each word in a list. This score places him in the Very Superior range, with a percentile rank of 99.87. This is consistent with Mr. X's academic level as a first-year graduate student, as well as with his habit of doing crossword puzzles. During the Vocabulary task, Mr. X took his time and thought carefully for each question. Then, he answered eloquently and completely, often giving far more information than necessary for a correct answer.
Mr. X also exhibited a significant weakness-he obtained a scaled score of 12 on the Symbol Search task, in which one must decide whether at least one of a pair of symbols is present in an adjacent 5-symbol set. This score places him in the High Average range, with a percentile rank of 75. Several factors may help explain this lower score: anxiety, attention, concentration, distractibility, motivation level, and work under time pressure. The Symbol Search task was the 12th out of 14 tasks. Therefore, it is possible that Mr. X's attention, concentration, and motivation level had waned. Also, Mr. X indicated some anxiety and concern about working under time pressure-during the task, he repeatedly verbalized distress that there were many items left he had not completed (which may have interfered with his task performance as well).