Chapter 5: Problem 2
Is the following statement correct? Explain why or why not. A correlation coefficient of 0 implies that no relationship exists between the two variables under study.
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Chapter 5: Problem 2
Is the following statement correct? Explain why or why not. A correlation coefficient of 0 implies that no relationship exists between the two variables under study.
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The article "The Epiphytic Lichen Hypogymnia physodes as a Bioindicator of Atmospheric Nitrogen and Sulphur Deposition in Norway" (Environmental Monitoring and Assessment [1993]: \(27-47\) ) gives the following data (read from a graph in the paper) on \(x=\mathrm{NO}_{3}\) wet deposition (in grams per cubic meter) and \(y=\) lichen (\% dry weight): a. What is the equation of the least-squares regression line? \(\quad \hat{y}=0.3651+0.9668 \mathrm{x}\) b. Predict lichen dry weight percentage for an \(\mathrm{NO}_{3}\) depo sition of \(0.5 \mathrm{~g} / \mathrm{m}^{3}\).
The following data on \(x=\) soil depth (in centimeters) and \(y=\) percentage of montmorillonite in the soil were taken from a scatterplot in the paper "Ancient Maya Drained Field Agriculture: Its Possible Application Today in the New River Floodplain, Belize, C.A." (Agricultural Ecosystems and Environment \([1984]: 67-84)\) : $$ \begin{array}{lllllllr} x & 40 & 50 & 60 & 70 & 80 & 90 & 100 \\ y & 58 & 34 & 32 & 30 & 28 & 27 & 22 \end{array} $$ a. Draw a scatterplot of \(y\) versus \(x\). b. The equation of the least-squares line is \(\hat{y}=64.50-\) \(0.45 x\). Draw this line on your scatterplot. Do there appear to be any large residuals? c. Compute the residuals, and construct a residual plot. Are there any unusual features in the plot?
For each of the following pairs of variables, indicate whether you would expect a positive correlation, a negative correlation, or a correlation close to \(0 .\) Explain your choice. a. Maximum daily temperature and cooling costs b. Interest rate and number of loan applications c. Incomes of husbands and wives when both have fulltime jobs d. Height and IQ e. Height and shoe size f. Score on the math section of the SAT exam and score on the verbal section of the same test g. Time spent on homework and time spent watching television during the same day by elementary school children h. Amount of fertilizer used per acre and crop yield (Hint: As the amount of fertilizer is increased, yield tends to increase for a while but then tends to start decreasing.)
The accompanying data represent \(x=\) the amount of catalyst added to accelerate a chemical reaction and \(y=\) the resulting reaction time: $$ \begin{array}{rrrrrr} x & 1 & 2 & 3 & 4 & 5 \\ y & 49 & 46 & 41 & 34 & 25 \end{array} $$ a. Calculate \(r\). Does the value of \(r\) suggest a strong linear relationship? b. Construct a scatterplot. From the plot, does the word linear really provide the most effective description of the relationship between \(x\) and \(y\) ? Explain.
A sample of automobiles traversing a certain stretch of 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 traverse this segment of highway. Would the sample correlation coefficient be closest to \(.9, .3,-.3\), or \(-.9 ?\) Explain.
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