a. Find the mean first = sum of scores/number of scores
Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.
Standard deviation = square root of variance
b. Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.
c. Z = (score-mean)/SD
d. Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.10) related to the Z score.
I'll let you do the calculations.
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 SumX=1008, and Sum(X-M)^2=140.4. Use this information to answer the following:
a. What is the mean and SD for this data?
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?
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?
2 answers
I found the mean but i do not know what the scores are. help. thanks