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Ch. 10 - Correlation and Regression
Triola - Elementary Statistics 14th Edition
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Tutti i libri di testoTriola 14th EditionCh. 10 - Correlation and RegressionProblema 10.2.6
Capitolo 10, Problema 10.2.6

Making Predictions
In Exercises 5–8, let the predictor variable x be the first variable given. Use the given data to find the regression equation and the best predicted value of the response variable. Be sure to follow the prediction procedure summarized in Figure 10-5. Use a 0.05 significance level.


Bear Measurements Head widths (in.) and weights (lb) were measured for 20 randomly selected bears (from Data Set 18 “Bear Measurements” in Appendix B). The 20 pairs of measurements yield xbar = 6.9 in., ybar = 214.3 lb, r = 0.879 P-value = 0.000 and y^ = -212 + 61.9x. Find the best predicted weight of a bear given that the bear has a head width of 6.5 in.

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Step 1: Understand the problem. We are tasked with predicting the weight of a bear (response variable y) given its head width (predictor variable x = 6.5 in.) using the provided regression equation ŷ = -212 + 61.9x. Additionally, we need to ensure the regression model is appropriate for making predictions by following the prediction procedure outlined in Figure 10-5.
Step 2: Verify the significance of the regression model. The problem states that the P-value is 0.000, which is less than the significance level of 0.05. This indicates that the regression model is statistically significant and can be used for making predictions.
Step 3: Check whether the given x-value (6.5 in.) is within the scope of the data. The mean head width (x̄) is 6.9 in., and since the x-value of 6.5 in. is reasonably close to the mean and likely within the range of the data, it is appropriate to use the regression equation for prediction.
Step 4: Substitute the given x-value (6.5 in.) into the regression equation ŷ = -212 + 61.9x. This involves replacing x with 6.5 and simplifying the expression: ŷ = -212 + 61.9(6.5).
Step 5: Simplify the expression to calculate the predicted weight ŷ. This will give the best predicted weight of the bear with a head width of 6.5 in. Ensure the units of the prediction are consistent with the response variable (pounds).

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Regression Equation

A regression equation models the relationship between a predictor variable (x) and a response variable (y). In this case, the equation y^ = -212 + 61.9x indicates how changes in head width (x) affect the predicted weight (y) of the bear. The coefficients represent the intercept and slope, respectively, allowing for predictions based on the value of x.
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Calculating Standard Deviation

Significance Level

The significance level, often denoted as alpha (α), is a threshold used to determine whether the results of a statistical test are significant. In this context, a 0.05 significance level means that there is a 5% risk of concluding that a relationship exists when there is none. It helps in making decisions about the validity of the regression model based on the p-value.
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Step 4: State Conclusion Example 4

Best Predicted Value

The best predicted value refers to the estimated response variable (y) obtained by substituting a specific value of the predictor variable (x) into the regression equation. For example, to find the predicted weight of a bear with a head width of 6.5 inches, you would substitute x = 6.5 into the regression equation, yielding the best estimate of the bear's weight based on the model.
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Critical Values: t-Distribution
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Finding the Best Model

In Exercises 5–16, construct a scatterplot and identify the mathematical model that best fits the given data. Assume that the model is to be used only for the scope of the given data, and consider only linear, quadratic, logarithmic, exponential, and power models.

Dirt Cheap The Cherry Hill Construction company in Branford, CT sells screened topsoil by the “yard,” which is actually a cubic yard. Let the variable x be the length (yd) of each side of a cube of screened topsoil. The table below lists the values of x along with the corresponding cost (dollars).

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Finding the Best Model

In Exercises 5–16, construct a scatterplot and identify the mathematical model that best fits the given data. Assume that the model is to be used only for the scope of the given data, and consider only linear, quadratic, logarithmic, exponential, and power models.

Stock Market Listed below in order by row are the annual high values of the Dow Jones Industrial Average for each year beginning with 2000. Find the best model and then predict the value for the last year listed. Is the predicted value close to the actual value of 26,828.4?

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Testing for a Linear Correlation

In Exercises 13–28, construct a scatterplot, and find the value of the linear correlation coefficient r. Also find the P-value or the critical values of r from Table A-6. Use a significance level of α = 0.05. Determine whether there is sufficient evidence to support a claim of a linear correlation between the two variables. (Save your work because the same data sets will be used in Section 10-2 exercises.)

Taxis The table below includes data from New York City taxi rides (from Data Set 32 “Taxis” in Appendix B). The distances are in miles, the times are in minutes, the fares are in dollars, and the tips are in dollars. Is there sufficient evidence to support the claim that there is a linear correlation between the time of the ride and the tip amount? Does it appear that riders base their tips on the time of the ride?


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Super Bowl and R^2 Let x represent years coded as 1,1,3,... for years starting in 1980, and let y represent the numbers of points scored in each annual Super Bowl beginning in 1980. Using the data from 1980 to the last Super Bowl at the time of this writing, we obtain the following values of R^2 for the different models: linear: 0.008; quadratic: 0.023; logarithmic: 0.0004; exponential: 0.027; power: 0.007. Based on these results, which model is best? Is the best model a good model? What do the results suggest about predicting the number of points scored in a future Super Bowl game?

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Finding the Best Model

In Exercises 5–16, construct a scatterplot and identify the mathematical model that best fits the given data. Assume that the model is to be used only for the scope of the given data, and consider only linear, quadratic, logarithmic, exponential, and power models.

CD Yields The table lists the value y (in dollars) of \$1000 deposited in a certificate of deposit at Bank of New York (based on rates currently in effect).

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Testing for a Linear Correlation

In Exercises 13–28, construct a scatterplot, and find the value of the linear correlation coefficient r. Also find the P-value or the critical values of r from Table A-6. Use a significance level of α = 0.05. Determine whether there is sufficient evidence to support a claim of a linear correlation between the two variables. (Save your work because the same data sets will be used in Section 10-2 exercises.)

Taxis Using the data from Exercise 15, is there sufficient evidence to support the claim that there is a linear correlation between the distance of the ride and the tip amount? Does it appear that riders base their tips on the distance of the ride?

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