Chapter 4: Problem 40
Briefly explain why a small value of \(s_{e}\) is desirable in a regression setting.
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Chapter 4: Problem 40
Briefly explain why a small value of \(s_{e}\) is desirable in a regression setting.
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It may seem odd, but biologists can tell how old a lobster is by measuring the concentration of pigment in the lobster's eye. The authors of the paper "Neurolipofuscin Is a Measure of Age in Panulirus argus, the Caribbean Spiny Lobster, in Florida" (Biological Bulletin [2007]: 55-66) wondered if it was sufficient to measure the pigment in just one eye, which would be the case if there is a strong relationship between the concentration in the right eye and the concentration in the left eye. Pigment concentration (as a percentage of tissue sample) was measured in both eyes for 39 lobsters, resulting in the following summary quantities (based on data from a graph in the paper): $$ \begin{array}{cll} n=39 & \sum_{x}=88.8 & \sum y=86.1 \\ \sum x y=281.1 & \sum x^{2}=288.0 & \sum y^{2}=286.6 \end{array} $$ An alternative formula for calculating the correlation coefficient that doesn't involve calculating the z-scores is $$ r=\frac{\sum_{x y}-\frac{\left(\sum x\right)\left(\sum y\right)}{n}}{\sqrt{\sum x^{2}-\frac{\left(\sum x\right)^{2}}{n}} \sqrt{\sum y^{2}-\frac{\left(\sum y\right)^{2}}{n}}} $$ Use this formula to calculate the value of the correlation coefficient, and interpret this value.
For a given data set, the sum of squared deviations from the line \(y=40+6 x\) is \(529.5 .\) For this same data set, which of the following could be the sum of squared deviations from the least squares regression line? Explain your choice. i. 308.6 ii. 529.6 iii. 617.4
Briefly explain why it is important to consider the value of \(s\) in addition to the value of \(r^{2}\) when evaluating the usefulness of the least squares regression line.
Data on \(y=\) time to complete a task (in minutes) and \(x=\) number of hours of sleep on previous night were used to find the least squares regression line. The equation of the line was \(\hat{y}=12-0.36 x .\) For this data set, would the sum of squared deviations from the line \(y=12.5-0.5 x\) be larger or smaller than the sum of squared deviations from the least squares regression line? Explain your choice. (Hint: Think about the definition of the least- squares regression line.)
A sample of automobiles traveling on a particular segment of a highway is selected. Each one travels at roughly a constant rate of speed, although speed does vary from auto to auto. Let \(x=\) speed and \(y=\) time needed to travel this segment. Would the sample correlation coefficient be closest to \(0.9,0.3,-0.3,\) or \(-0.9 ?\) Explain.
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