Question 1. Jason is a 33-year-old man who was administered the fourth edition of the Peabody Picture Vocabulary Test (PPVT-IV), a test of receptive vocabulary. The PPVT-IV is a test where Jason was told a word and asked to indicate which of four pictures best represented that word. He was able to correctly associate pictures with words on a total of 214 items and obtained a Standard Score of 107. The reliability of the PPVT-IV for someone of Jason’s age is .94. (4 marks)
| a. What is the percentile rank that corresponds to his Standard Score of 107 (rounded to the nearest whole number) | ||
| b. Compute the 90% confidence interval for his Standard Score of 107 (rounded to the nearest whole number) | ||
| c. Jason obtained a Scaled Score of 8 on the Vocabulary subtest of the fourth edition of the Wechsler Adult Intelligence Scale (WAIS-IV), a test of expressive vocabulary. What is the percentile rank that corresponds to his Scaled Score of 8 (rounded to the nearest whole number)? | ||
| d. You would like to compare his performance on the PPVT-IV with the Vocabulary test but they are on different scales. Using the z score you computed in (1a) to determine the percentile rank, convert his PPVT score to the equivalent Scaled Score (rounded to the nearest whole number). |
Question 2. Annette is a 54-year-old woman who was administered the National Adult Reading Test (NART). She incorrectly pronounced 39 of the 50 words giving her a total raw score of 39 errors. For a woman of her age and level of education, the sample error mean was 25.0 and the standard deviation was 11.67. The reliability of the NART is .93. (3 marks)
| a. What is the percentile rank that corresponds to her score of 39 (rounded to the nearest whole number) | ||
| b. Compute the 90% confidence interval for her score of 39 (rounded to the nearest whole number) | ||
| c. Using the z score you computed in (2a) to determine the percentile rank, convert this to the equivalent Standard Score. |
Question 3. Edward is a 72-year-old man who has been experiencing memory lapses and has become increasingly concerned about his cognitive abilities. You assess him with the second edition of the Dementia Rating Scale (DRS2) and he obtains a total score of 135 out of 144 (the higher the score the better the performance). The reliability for the DRS2 is .84, the mean is 138.2, and the standard deviation is 8.0. (4 marks)
| a. What is the percentile rank that corresponds to his total score of 135 (rounded to the nearest whole number) | ||
| b. Compute the 90% confidence interval for his total score of 135 (rounded to the nearest whole number) |
A year later, Edward returns concerned that his memory has continued to decline. You again test him with the DRS and this time he obtains a total score of 102.
| c. Using his initial score of 135 compute a 90% retest confidence interval. | |||
| d. Comparing his current score of 102 with the retest confidence interval, does the evidence suggest that Edward’s memory has declined? Why? | |||
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Question 4. Jorge is applying for a position on an assembly line where it will be important for him to be able to work quickly and efficiently. You have been hired as a psychologist to screen applicants for their speed and manual dexterity and to do this you administer the Lafayette Grooved Pegboard, a test where the applicant must quickly rotate grooved pegs in order to fit them into similarly shaped holes. You measure how long it takes for the applicant to successfully put 10 pegs into 10 holes. Jorge completes the task in 43.6 seconds. The mean time for completing the task for workers in the job for which he is applying is 22.4 seconds with a standard deviation of 9.4 seconds. The reliability for the test is .72. (3 marks)
| a. What is the percentile rank that corresponds to Jorge’s completion time of 43.6 seconds (rounded to the nearest whole number) | |||
| b. Compute the 90% confidence interval for his time of 43.6 seconds (rounded to the nearest whole number) | |||
| c. Based on these findings would you consider that Jorge is likely to have the required skills to perform the job for which he has applied? Why? | |||
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Question 5. Annalise was 23-years-old when she sustained a head injury in a motor-vehicle accident three years ago. Since then she has experienced ongoing difficulties with her memory and concentration. You assessed her one year after her accident with the fourth edition of the Wechsler Memory Scale (WMS-IV) and she obtained a Standard Score of 75 on the Immediate Memory Index. The reliability of the WMS-IV Immediate Memory Index is .95 (6 marks)
| a. What is the percentile rank that corresponds to Annalise’s Immediate Memory Index score (rounded to the nearest whole number) | ||
| b. Compute the 95% confidence interval for her score on the Immediate Memory Index (rounded to the nearest whole number) |
It is now two-years later and you have reassessed Annalise to determine if her memory has improved in the intervening time. On this occasion she obtains a Standard Scores of 92 on the Immediate Memory Index.
| c. What is the percentile rank that corresponds to Annalise’s Immediate Memory Index score from this assessment (rounded to the nearest whole number) | |||
| d. Compute the 95% confidence interval for her current score on the Immediate Memory Index (rounded to the nearest whole number) | |||
| e. Using the Immediate Memory Index score from the first assessment compute a 95% retest confidence interval for Immediate Memory. | |||
| f. Compare Annalise’s current Immediate Memory Score with the retest confidence interval? Does it indicate that the change in Annalise’s score constitutes real improvement or just variation associated with the psychometric properties of the test? Why? | |||
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