Chapter 13: Problem 34
Explain the difference between a confidence interval and a prediction interval. How can a prediction level of \(95 \%\) be interpreted?
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Chapter 13: Problem 34
Explain the difference between a confidence interval and a prediction interval. How can a prediction level of \(95 \%\) be interpreted?
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An investigation of the relationship between traf. fic flow \(x\) (thousands of cars per \(24 \mathrm{hr}\) ) and lead content \(y\) of bark on trees near the highway (mg/g dry weight) yielded the accompanying data. A simple linear regression model was fit, and the resulting estimated regression line was \(\hat{y}=28.7+33.3 x .\) Both residuals and standardized residuals are also given. a. Plot the \((x\), residual \()\) pairs. Does the resulting plot suggest that a simple linear regression model is an appropriate choice? Explain your reasoning. b. Construct a standardized residual plot. Does the plot differ significantly in general appearance from the plot in Part (a)?
The data of Exercise \(13.25\), in which \(x=\) milk temperature and \(y=\) milk \(\mathrm{pH}\), yield $$ \begin{aligned} &n=16 \quad \bar{x}=43.375 \quad S_{x x}=7325.75 \\ &b=-.00730608 \quad a=6.843345 \quad s_{e}=.0356 \end{aligned} $$ a. Obtain a \(95 \%\) confidence interval for \(\alpha+\beta(40)\), the true average milk \(\mathrm{pH}\) when the milk temperature is \(40^{\circ} \mathrm{C}\). b. Calculate a \(99 \%\) confidence interval for the true average milk pH when the milk temperature is \(35^{\circ} \mathrm{C}\). c. Would you recommend using the data to calculate a \(95 \%\) confidence interval for the true average \(\mathrm{pH}\) when the temperature is \(90^{\circ} \mathrm{C}\) ? Why or why not?
The flow rate in a device used for air quality measurement depends on the pressure drop \(x\) (inches of water) across the device's filter. Suppose that for \(x\) values between 5 and 20 , these two variables are related according to the simple linear regression model with true regression line \(y=-0.12+0.095 x\). a. What is the true average flow rate for a pressure drop of 10 in.? A drop of 15 in.? b. What is the true average change in flow rate associated with a 1 -in. increase in pressure drop? Explain. c. What is the average change in flow rate when pressure drop decreases by 5 in.?
Suppose that a regression data set is given and you are asked to obtain a confidence interval. How would you tell from the phrasing of the request whether the interval is for \(\beta\) or for \(\alpha+\beta x^{*} ?\)
The article "Cost-Effectiveness in Public Education" (Chance [1995]: \(38-41\) ) reported that, for a sample of \(n=44\) New Jersey school districts, a regression of \(y=\) average SAT score on \(x=\) expenditure per pupil (thousands of dollars) gave \(b=15.0\) and \(s_{b}=5.3\). a. Does the simple linear regression model specify a useful relationship between \(x\) and \(y\) ? b. Calculate and interpret a confidence interval for \(\beta\) based on a \(95 \%\) confidence level.
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