Age at onset of dementia was determined for the sample of adults between ages of 60 and 75. For 15 subjects, the results were EX=1008, and E(X-M)^2 = 140.4. Employ this information to answer the following:
A) Determine the mean and SD for this data?
B) Based upon the data you've and the Normal Curve Tables, what percentage of people may start to show signs of dementia at or before age 62?
C) If we suggest 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?