/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 43 Most cars are fuel efficient whe... [FREE SOLUTION] | 91Ó°ÊÓ

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Most cars are fuel efficient when running at a steady speed of around 40 to \(50 \mathrm{mph}\). A scatterplot relating fuel consumption (measured in mpg) and steady driving speed (measured in mph) for a mid-sized car is shown below. The data are available in the Fuel file on the book's Web site. (Source: Berry, I. M. (2010). The Effects of Driving Style and Vehicle Performance on the Real-World Fuel Consumption of U.S. Light-Duty Vehicles. Masters thesis, Massachusetts Institute of Technology, Cambridge, MA.) a. The correlation equals \(0.106 .\) Comment on the use of the correlation coefficient as a measure for the association between fuel consumption and steady driving speed. b. Comment on the use of the regression equation as a tool for predicting fuel consumption from the velocity of the car. c. Over what subrange of steady driving speed might fitting a regression equation be appropriate? Why?

Short Answer

Expert verified
The correlation is too weak for reliable predictions. A focused regression might work on the 40-50 mph range.

Step by step solution

01

Understanding Correlation

The correlation coefficient of 0.106 indicates a very weak positive linear relationship between fuel consumption and steady driving speed. Since this value is close to 0, it suggests that there is little to no linear association between the two variables.
02

Evaluating Regression Equation Usage

Due to the weak correlation, a regression model for predicting fuel consumption based on speed would likely be unreliable. Such a low correlation indicates that other factors, aside from speed, play a larger role in determining fuel consumption.
03

Identifying Appropriate Subrange

To find a subrange where fitting a regression equation might be appropriate, look for sections of the scatterplot where the data shows more consistency or a stronger linear trend. Since most cars are most efficient at speeds around 40 to 50 mph, as mentioned, this range might exhibit a clearer relationship, making it suitable for a more focused regression analysis.

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Key Concepts

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

Scatterplot Analysis
A scatterplot is a visual representation of the relationship between two numerical variables. It shows data points plotted on a horizontal and vertical axis, where each point represents an observation from your dataset. In the context of the fuel consumption study, each point on the scatterplot reflects a car's steady driving speed and the corresponding fuel efficiency.

When analyzing scatterplots, one can look for patterns, trends, or associations between the two variables. For this study, the key question was whether higher speeds led to better or worse fuel efficiency. The strength and direction of this relationship can reveal valuable insights.

Though we might expect fuel efficiency to improve up to a certain speed threshold, as indicated by the dataset, the scatterplot alone doesn't quantify the strength of this relationship but helps us visualize it. Noticing whether the plotted points form a particular shape (like forming a line) can further guide analysis. A random distribution of points with no discernible pattern might imply a weak association between the variables.
Regression Equation
The regression equation provides a mathematical method to describe the relationship between two variables, offering predictions. Its basic form in statistics is often a line: \[ y = mx + c \]where \(y\) is the dependent variable, \(x\) is the independent variable, \(m\) is the slope of the line, and \(c\) is the y-intercept.

In the study of fuel consumption, the regression line aims to describe how fuel efficiency changes with varying speeds. However, with a correlation coefficient of 0.106, suggesting a very weak linear relationship, the regression equation may not reliably predict fuel consumption based on speed alone.

The main limitation here is that regression can only account for linear relationships effectively. If other factors significantly influence fuel consumption, such as car weight or engine efficiency, these must be considered to create a robust predictive model. Hence, while the regression equation can be a starting tool, its current predictive power is limited by the correlation strength observed.
Fuel Consumption Study
A fuel consumption study, like the one described in the exercise, aims to understand how different driving speeds impact how efficiently a car uses fuel. This helps in identifying optimal speeds where cars may operate most economically.

While the general hypothesis might be that a moderate speed (40-50 mph) is most efficient, this study sought to verify that through data by plotting various speeds against fuel efficiency in a scatterplot.
  • Data Collection: Gather data on car speeds and their corresponding fuel consumption.
  • Analysis: Using scatterplots to identify patterns or trends in data.
  • Conclusion: Trying to find a speed range where cars are most fuel-efficient.
This information is crucial for drivers aiming to reduce their fuel costs and for policymakers looking to promote more sustainable driving habits. By identifying the ideal range of speed, the study not only underscores practical advice for individual drivers but also helps inform broader initiatives for vehicle efficiency. Thus, a well-executed study has the potential to benefit individual and public interests significantly.

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Most popular questions from this chapter

Zagat restaurant guides publish ratings of restaurants for many large cities around the world (see www.zagat.com). The review for each restaurant gives a verbal summary as well as a 0 - to 30 -point rating of the quality of food, décor, service, and the cost of a dinner with one drink and tip. For 31 French restaurants in Boston in \(2014,\) the food quality ratings had a mean of 24.55 and standard deviation of 2.08 points. The cost of a dinner (in U.S. dollars) had a mean of \(\$ 50.35\) and standard deviation of \(\$ 14.92\). The equation that predicts the cost of a dinner using the rating for the quality of food is \(\hat{y}=-70+4.9 x\). The correlation between these two variables is 0.68 . (Data available in the Zagat_Boston file.) a. Predict the cost of a dinner in a restaurant that gets the (i) lowest observed food quality rating of \(21,\) (ii) highest observed food quality rating of 28 . b. Interpret the slope in context. c. Interpret the correlation. d. Show how the slope can be obtained from the correlation and other information given.

For students who take Statistics 101 at Lake Wobegon College in Minnesota, both the midterm and final exams have mean \(=75\) and standard deviation \(=10 .\) The professor explores using the midterm exam score to predict the final exam score. The regression equation relating \(y=\) final exam score to \(x=\) midterm exam score is \(\hat{y}=30+0.60 x\). a. Find the predicted final exam score for a student who has (i) midterm score \(=100,\) (ii) midterm score \(=50\). Note that in each case the predicted final exam score regresses toward the mean of \(75 .\) (This is a property of the regression equation that is the origin of its name, as Chapter 12 will explain.) b. Show that the correlation equals 0.60 and interpret it. (Hint: Use the relation between the slope and correlation.)

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According to data obtained from the General Social Survey (GSS) in 2014,1644 out of 2532 respondents were female and interviewed in person, 551 were male and interviewed in person, 320 were female and interviewed over the phone and 17 were male and interviewed over the phone. a. Explain how we could regard either variable (gender of respondent, interview type) as a response variable. b. Display the data as a contingency table, labeling the variables and the categories. c. Find the conditional proportions that treat interview type as the response variable and gender as the explanatory variable. Interpret. d. Find the conditional proportions that treat gender as the response variable and interview type as the explanatory variable. Interpret. e. Find the marginal proportion of respondents who (i) are female, (ii) were interviewed in person.

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