.  Age at onset of dementia was determined for a sample of adults between the ages of 60 and 75. ...

.  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?