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NL baseball Example 9 related \(y=\) team scoring (per game) and \(x=\) team batting average for American League teams. For National League teams in 2010 , \(\hat{y}=-6.25+41.5 x\). (Data available on the book's website in the NL team statistics file.) a. The team batting averages fell between 0.242 and \(0.272 .\) Explain how to interpret the slope in context. b. The standard deviations were 0.00782 for team batting average and 0.3604 for team scoring. The correlation between these variables was 0.900 . Show how the correlation and slope of 41.5 relate in terms of these standard deviations. c. Software reports \(r^{2}=0.81 .\) Explain how to interpret this measure.

Short Answer

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a) The slope indicates a 0.0415 run increase for each 0.001 increase in batting average. b) The slope of 41.5 is consistent with the correlation and standard deviations. c) 81% of the variation in scoring is explained by batting average.

Step by step solution

01

Interpret the Slope

The slope of the regression line, \(41.5\), tells us how much the average team scoring changes for each 0.001 increase in the team batting average. In this context, it means that for every 0.001 increase in batting average, the team scoring increases by 0.0415 runs per game.
02

Relate Correlation and Slope

According to the formula for the slope of the regression line \(b = r \frac{s_y}{s_x}\), where \(r\) is the correlation coefficient, \(s_y\) is the standard deviation of the dependent variable, and \(s_x\) is the standard deviation of the independent variable. Substituting the given values: \(b = 0.900 \times \frac{0.3604}{0.00782} = 41.5\). This confirms that the slope is consistent with the correlation and standard deviations provided.
03

Interpret the Coefficient of Determination

The value \(r^2 = 0.81\) indicates that 81% of the variability in team scoring can be explained by their batting average. This means the linear model provides a strong fit to the data, showing that batting average is a strong predictor of team scoring in this context.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Correlation Coefficient
The correlation coefficient, denoted as \( r \), is a powerful statistic that shows how closely two variables are related. In the context of linear regression, it measures the strength and direction of a linear relationship between the independent variable \( x \) and the dependent variable \( y \). Here, the correlation coefficient is \( 0.900 \), indicating a very strong positive relationship between team batting average and team scoring. This means that as the team's batting average increases, so does their ability to score more points. - **Strong Positive Correlation**: Since \( r = 0.900 \) is close to 1, it implies a robust linear association between the two variables.- **Direction of Relationship**: Positive \( r \) value indicates that the variables move together in the same direction. As one variable increases, the other tends to increase as well.Understanding \( r \) is crucial as it not only suggests the presence of a linear relationship but also helps in determining how well changes in one variable can predict changes in another.
Slope Interpretation
In linear regression, the slope of the line is an essential component as it expresses how the dependent variable changes with respect to the independent variable. Given the regression equation for National League teams: \( \hat{y} = -6.25 + 41.5x \), the slope is 41.5. This number can tell us quite a bit when contextualized.- **Unit Change**: It reflects the average change in team scoring (\( y \)) for each 0.001 unit increase in the team's batting average (\( x \)). - For example, with a slope of 41.5, for every 0.001 increase in batting average, the average scoring increases by an average of 0.0415 runs per game.- **Contextual Interpretation**: This slope shows the sensitivity of team scoring to changes in batting averages. It suggests that even small improvements in batting can potentially lead to a noticeable increase in scoring, underlining the importance of batting averages in baseball strategies.
Coefficient of Determination
The coefficient of determination, represented as \( r^2 \), provides insight into how well the model explains the variation in the dependent variable. - In this case, \( r^2 = 0.81 \), indicating that 81% of the variation in team scoring is accounted for by the team's batting average. - **High \( r^2 \) Value**: It suggests that the batting average is a strong predictor of team scoring. - **Model Performance**: This high level of explained variance means the linear regression model fits the data well, offering valuable predictions about scoring.Understanding the coefficient of determination helps gauge the effectiveness of the regression model and the degree to which it can be trusted for predictive insights. It represents a summary measure of how well the model captures the actual data trends.

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Most popular questions from this chapter

Wage bill of Premier League Clubs Data of the Premier League Clubs' wage bills was obtained from www.tsmplug .com. For the response variable \(y=\) wage bill in millions of pounds in 2014 and the explanatory variable \(x=\) wage bill in millions of pounds in \(2013, \hat{y}=-1.537+1.056 x\). a. How much do you predict the value of a club's wage bill to be in 2014 if in 2013 the club had a wage bill of (i) \(£ 100\) million, (ii) \(£ 200\) million? b. Using the results in part a, explain how to interpret the slope. c. Is the correlation between these variables positive or negative? Why? d. A Premier League club had a wage bill of \(£ 100\) million in 2013 and \(£ 105\) million in \(2014 .\) Find the residual and interpret it.

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Go to the GSS website sda.berkeley.edu/ GSS, click GSS, with No Weight Variables predefined (SDA 4.0), type SEX for the row variable and HAPPY for the column variable, put a check in the row box only for percentaging in the output options, and click Run the Table. a. Report the contingency table of counts. b. Report the conditional proportions to compare the genders on reported happiness. c. Are females and males similar, or quite different, in their reported happiness? Compute and interpret the difference and ratio of the proportion of being not too happy between the two sexes.

Government debt and population \(\quad\) Data used in this exercise was published by www.bloomberg.com for the most government debt per person for 58 countries and their respective population sizes in 2014 . When using population size (in millions) as the explanatory variable \(x,\) and government debt per person (in dollars) as the response variable \(y,\) the regression equation is predicted as government debt per person \(=19560.405-13.495\) population. a. Interpret the slope of the regression equation. Is the association positive or negative? Explain what this means. b. Predict government debt per person at the (i) minimum population size \(x\) value of 4 million, (ii) at the maximum population size \(x\) value of 1367.5 million. c. For India, government debt per person \(=\$ 946,\) and population \(=1259.7\) million. Find the predicted gov. ernment debt per person and the residual for India. Interpret the value of this residual.

Each month, the owner of Fay's Tanning Salon records in a data file the monthly total sales receipts and the amount spent that month on advertising. a. Identify the two variables. b. For each variable, indicate whether it is quantitative or categorical. c. Identify the response variable and the explanatory variable.

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