. Age at onset of dementia was determined for a sample of adults between the ages of 60 and 75. For 15 subjects, the results were ΣX = 1008, and Σ (X-M)2 = 140.4. Use this information to answer the following:
a. What is the mean and SD for this data
M = 1008 /15 M = 67.2 SD= 140.4
b. Based on the data you have and the Normal Curve Tables, what percentage of people might start to show signs of dementia at or before age 62?
(62-67.2)
0.037
c. If we consider the normal range of onset in this population to be +/-1
Z-score from the mean, what two ages correspond to this?
d. A neuropsychologist is interested only in studying the most deviant portion of this population, that is, those individuals who fall within the top 10% and the bottom 10% of the distribution. She must determine the ages that mark these boundaries. What are these ages?
