Answers to questions missed on quiz three
Question one:
Given the following scenarios, in which case is the error of prediction
highest?
Scenario A: Among the population of one year old babies, 80% who have above average
weight also have above average height and 80% who have below average weight also
have below average height.
This is a positive correlation; pretty high. There is some
error of prediction.
Scenario B: For women in the 7080 year age range, 70% of the women who have below
average bone density have above average osteoporosis and 70% who have above average
bone density have below average osteoporosis.
This is negative correlation, pretty
high. There is some error of prediction.
Scenario C. In the population of adults as the size of the wrist increases, anxiety level
does not change.
This is zero correlation. Error of prediction is highest.
Scenario D. Keeping volume constant, 100% of the metals that have above average
density also have above average mass and 100% that have below average density also
have below average mass.
This is perfect positive correlation r = 1 . There is no error
of prediction
Hint: Before picking the right answer, draw the scatterplot corresponding to each
scenario.
Question two
What is the mean of the error in the following scenarios?
Scenario A: There are 30 bothers and sisters and in all cases the age of the brother is half
of the age of the sister.
Perfect correlation mean of error = 0
Scenario B: SAT quantitative and verbal scores for 30 students.
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 Fall '11
 Gould
 Correlation, Normal Distribution, Regression Analysis, Standard Deviation, Errors and residuals in statistics

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