Age at onset of dementia was estimated for sample of adults between ages of 60 and 75. For 15 subjects, the results were ?X = 1008, and ?(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 have and the Normal Curve Tables, what percentage of people may start to show signs of dementia at or before age 62?
c. If we consider the normal range of onset in this population to be +/-1 z-score from mean, what two ages correspond to this?
d. A neuropsychologist is interested only in studying most deviant portion of this population, that is, those individuals who fall in the top 10% and bottom 10% of the distribution. She must find out the ages that mark these boundaries. What are these ages?