SECTION I Number of Questions 42 Percent of Total Grade 50

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1 AP Stats Chap 7-9 Practice Test Name Pd SECTION I Number of Questions 42 Percent of Total Grade 50 Directions: Solve each of the following problems, using the available space (or extra paper) for scratchwork. Decide which is the best of the choices given and place that letter on the ScanTron sheet. No credit will be given for anything written on these pages for this part of the test. Do not spend too much time on any one problem. 1. In a statistics course, a linear regression equation was computed to predict the final exam score from the score on the first test. The equation was y = x where y is the final exam score and x is the score on the first test. Carla scored 95 on the first test. What is the predicted value of her score on the final exam? A. 95 B C. 90 D E. none of these 2. Refer to the previous problem. On the final exam, Carla scored 98. What is the value of her residual? A. 98 B. 2.5 C D. 0 E. none of these 3. A study of the fuel economy for various automobiles plotted the fuel consumption (in liters of gasoline used per 100 kilometers traveled) versus speed (in kilometers per hour). A Least Squares Regression Line (LSRL) was fit to the data. Here is the residual plot from this least squares fit. What does the pattern of the residuals tell you about the linear model? A. The evidence is inconclusive. B. The residual plot confirms the linearity of the fuel economy data. C. The residual plot does not confirm the linearity of the data. D. The residual plot clearly contradicts the linearity of the data. E. None of the above. 4. All but one of the following statements contains a blunder. Which statement is correct? A. There is a correlation of 0.54 between the position a football player plays and his weight. B. The correlation between planting rate and yield of corn was found to be r = C. The correlation between the gas milage of a car and its weight is r = 0.71 mpg. D. We found a high correlation (r = 1.09) between the height and age of children. E. We found a correlation of r = between gender and political party preference.

2 5. The correlation r for the data in this scatterplot is A. near -1 B. clearly negative, but not near -1 C. near 0 D. clearly positive, but not near 1 E. near 1 6. In the scatterplot in the previous question, if each x-value were decreased by one unit and the y-values remained the same, then the correlation r would A. decrease by 1 unit B. decrease slightly C. increase slightly D. stay the same E. you can t tell without knowing the data values 7. In regression, the residuals are which of the following? A. those factors unexplained by the data B. the difference between the observed responses and the values predicted by the regression line C. those data points which were recorded after the formal investigation was completed D. possible models unexplored by the investigator E. none of these 8. What does the square of the correlation measure? A. the slope of the LSRL B. the intercept of the LSRL C. the extent to which cause and effect is present in the data D. the percent of the variation in the values of y that is explained by least squares regression on the other E. the strength of the linear association between the variables 9. Which of the following statements are true? I. Correlation and regression require explanatory and response variables. II. Scatterplots require that both variables be quantitative. III. Every LSRL passes through ( x,y ) A. I and II only B. I and III only C. II and III only D. I, II, and III E. none of these 10. A local community college announces the correlation between college entrance exam grades and scholastic achievement was found to be On the basis of this, you would tell the college that A. the entrance exam is a good predictor of success. B. the exam is a poor predictor of success. C. students who do best on this exam will be poor students. D. students at this school are underachieving. E. the college should hire a new statistician.

3 11. A researcher finds that the correlation between the personality traits greed and superciliousness is What percentage of the variation in greed can be explained by the relationship with superciliousness? A. 0% B. 16% C. 20% D. 40% E. 60% 12. Suppose the following information was collected, where x = diameter of tree trunk in inches, and y = tree height in feet. x y If the LSRL equation is y = x, what is your estimate of the average height of all trees having a trunk diameter of 7 inches? A B C D E Suppose we fit the LSRL to a set of data. What is true if a plot of the residuals shows a curved pattern? A. A straight line is not a good model for the data. B. The correlation must be 0. C. The correlation must be positive. D. Outliers must be present. E. The LSRL might or might not be a good model for the data, depending on the extent of the curve. 14. The following is / are resistant to drastic, unusual data: A. least squares regression line B. correlation coefficient C. both the least squares line and the correlation coefficient D. neither the least squares line nor the correlation coefficient E. it depends 15. A study found correlation r = 0.61 between the sex of a worker and his or her income. You conclude that A. women earn more than men on average. B. women earn less than men on average. C. an arithmetic mistake was made; this is not a possible value of r. D. there may be a lurking variable that is causing a moderately strong relationship. E. there is a moderately strong, positive, linear relationship between sex and income. 16. A copy machine dealer has data on the number x of copy machines at each of 89 customer locations and the number y of service calls in a month at each location. Summary calculations give x = 8.4, sx = 2.1, y = 14.2, sy = 3.8, and r = What is the slope of the LSRL of number of service calls on number of copiers? A B C D. none of these E. you can t tell from the information given

4 17. In the setting of the previous problem, about what percent of the variation in the number of service calls is explained by the linear relation between number of service calls and the number of machines? A. 86% B. 93% C. 74% D. none of these E. you can t tell from the information given 18. If Data Set A of (x, y) data has correlation coefficient r = 0.65, and a second Data Set B has correlation r = -0.65, then A. the points in A exhibit a stronger linear association than B. B. the points in B exhibit a stronger linear association than A. C. neither A or B has a very strong linear association. D. you can t tell which data set has a stronger linear association without seeing the data or seeing the scatterplots. E. A and B are actually the same data set. 19. There is a linear relationship between the number of chirps made by the striped ground cricket and the air temperature. A least squares fit of some data collected by a biologist give the model ŷ = x (when x is between 9 and 25), where x is the number of chirps per minute and ŷ is the estimated temperature in degrees Fahrenheit. What is the estimated increase in temperature that corresponds to an increase in 5 chirps per minute? A. 3.3 F B F C F D F E F 20. The equation of the LSRL for a certain set of data is ŷ = x. What is the residual for the point (4, 7)? A B C D E A set of data relates the amount of annual salary raise and the performance rating an employee receives. The least squares regression equation is ŷ = x where y is the estimated raise and x is the performance rating. Which of the following statements is not correct? A. For each increase of one point in performance rating, the raise will increase on average by $2,000. B. This equation produces predicted raises with an average error of 0. C. A rating of 0 will yield a predicted raise of $1,400. D. The correlation for the data is positive. E. All of the above are true. 22. Suppose we fit the LSRL to a set of data. What do we call any individual points with unusually large values of the residuals? A. response variables B. the slope C. outliers D. correlations E. none of these

5 23. The effect of removing the right-most point (near the positive x-axis) in the scatterplot shown would be that A. the slope of the LSRL will increase; r will increase. B. the slope of the LSRL will increase; r will decrease. C. the slope of the LSRL will decrease; r will increase. D. the slope of the LSRL will decrease; r will decrease. E. there will be no change. 24. If removing an observation from a data set would have a marked change on the position of the LSRL fit to the data, what is the point called? A. robust B. a residual C. a response D. influential E. none of these 25. Which of the following statements are correct? I. Two quantitative variables that are strongly associated will have a correlation near 1. II. Regression requires an explanatory-response relationship, while correlation does not. III. Even though the correlation between two variables may be high, in order to use the LSRL to predict, there needs to be an explanatory-response relationship between x and y. A. I and II only B. I and III only C. II and III only D. I, II, and III E. none of these gives the complete set of true responses 26. Suppose the correlation between two variables x and y is due to the fact that both are responding to changes in some unobserved third variable. What is this due to? A. cause and effect between x and y B. the effect of a lurking variable C. extrapolation D. common sense E. none of these 27. Suppose a straight line is fit to data having response variable y and explanatory variable x. Predicting values of y for values of x outside the range of the observed data is called A. correlation B. causation C. extrapolation D. sampling E. none of these 28. Which of the following is / are true statements? I. High correlation does not necessarily imply causation. II. A lurking variable is a name given to variables that cannot be identified or explained. III. Successful prediction requires a cause and effect relationship. A. I only B. II only C. III only D. I and II only E. none of these

6 29. There is a positive association between the number of local river drownings and ice cream sales at lunch in the cafeteria. This is an example of an association likely caused by A. lurking variable B. cause and effect relationship C. a confounding factor D. common response E. none of these 30. If the correlation between body weight and annual income were high and positive, we could conclude that A. high incomes cause people to eat more food. B. low incomes cause people to eat less food. C. high-income people tend to spend a greater proportion of their income on food than low-income people, on average. D. high-income people tend to be heavier than low-income people, on average. E. high incomes cause people to gain weight. 31. A study examined the relationship between the sepal length and sepal width for two varieties of an exotic tropical plant. Variety A and Variety B are represented by x s and o s, respectively, in the following plot: Which of the following statements is false? A. Considering Variety A alone, there is a negative correlation between sepal length and sepal width. B. Considering Variety B alone, the least squares regression line for predicting sepal length from sepal width has a negative slope. C. Considering both varieties together, there is a positive correlation between sepal length and sepal width. D. Considering each variety separately, there is a positive correlation between sepal length and sepal width. E. Considering both varieties together, the least squares regression line for predicting sepal length from sepal width has a positive slope. 32. Which statement about influential points is true? I. Removal of an influential point changes the regression line. II. Data points that are outliers in the horizontal direction are more likely to be influential than points that are outliers in the vertical direction. III. Influential points have large residuals. A. I only B. I and II C. I and III D. II and III E. I, II, and III

7 33. The model strength = ( diameter) 2 can be used to predict the breaking strength of a rope (in pounds) from its diameter (in inches). According to this model, how much force should a rope one-half inch in diameter be able to withstand? A. 4.7 lbs B. 16 lbs C. 22 lbs D. 256 lbs E. 484 lbs 34. One of the three flavors of unusual points is the type that confirms the pattern, but is an extreme data point. These points I. have high leverage and large residuals. 2 II. have negligible effect on the value of R. III. have no impact on the slope of the line of best fit, but greatly change its y-intercept. A. II only B. III only C. I and II D. all of these are true E. none of these are true 35. A residuals plot is helpful because I. it will help us see whether our model is appropriate. II. it might show a pattern in the data that was hard to see in the original scatterplot. III. it will clearly identify influential points. A. I only B. II only C. I and II only D. I and III only E. I, II, and III 36. Which is true? I. Random scatter in the residuals indicates a model with high predictive power. II. If two variables are very strongly associated, then the correlation between them will be near +1.0 or 1.0. III. The higher the correlation between two variables, the more likely the association is based on cause and effect. A. none of these B. I only C. II only D. I and II only E. I, II, and III 37. If the point in the upper right corner of this scatterplot is removed from the data set, then what will happen to the slope of the line of best fit, b, and to the correlation, r? A. both will increase B. both will decrease C. b will increase, and r will decrease D. b will decrease, and r will increase E. both will remain the same

8 38. All but one of the statements below contain a mistake. Which one could be true? A. The correlation between height and weight is inches per pound. B. The correlation between weight and length of foot is C. The correlation between the breed of a dog and its weight is D. The correlation between gender and age is E. If the correlation between blood alcohol level and reaction time is 0.73, then the correlation between reaction time and blood alcohol level is A regression analysis of students college Grade Point Averages and their high school GPAs 2 found R = Which of these is true? I. High school GPA accounts for 31.1% of college GPA. II. 31.1% of college GPAs can be correctly predicted with this model. III. 31.1% of the variance in college GPA can be accounted for by this model. A. I only B. II only C. III only D. I and II E. none 40. When using midterm exam scores to predict a student s final grade in a class, the student would prefer to have a A. positive residual, because that means the student s final grade is higher than we would predict with this model. B. positive residual, because that means the student s final grade is lower than we would predict with this model. C. residual equal to zero, because that means the student s final grade is exactly what we would predict with the model. D. negative residual, because that means the student s final grade is higher than we would predict with this model. E. negative residual, because that means the student s final grade is lower than we would predict with the model. 41. Using the scatterplot shown and the stray point, which of the following is true? I. The stray point has little leverage, but a large residual. II. The stray point is not influential. III. If the stray point were removed from the data, the correlation would become stronger and become more negative because scatter would decrease. A. I only B. I and III only C. II and III only D. all of these are true E. none of these are true

9 42. When extrapolating using a model, A. don t extrapolate much, if at all. B. extrapolate only within the data you have been given. C. extrapolate only up to five points past your last data point, but no further. D. there are no clear guidelines on extrapolating, so do as you please. E. never, never, never extrapolate. SECTION II Questions Percent of Total Grade 50 Directions: Show all of your work. Indicate clearly the methods you use, because you will be graded on the correctness of your methods as well as on the accuracy of your results and explanations. Assembly Line. Your new job at Panasony is to do the final assembly of camcorders. As you learn how, you get faster. The company tells you that you will qualify for a raise if, after 13 weeks, your assembly time averages under 20 minutes. The data shows your average assembly time during each of your first 10 weeks. Week Time (min) Which is the explanatory variable? What is the correlation between these variables? You want to predict whether or not you will quality for that raise. Would is be appropriate to use a linear model? Defend your position.

10 Associations. For each pair of variables, indicate what association you expect. Use P for positive, N for negative, C for curved, or O for none. 46. Power level setting of a microwave and number of minutes it takes to boil water Number of days it rained in a month during the summer and number of times you mowed your lawn that month Number of hours a person has been up past a normal bedtime and number of minutes it takes the person to do a crossword puzzle Number of hockey games played in Minnesota during a week and sales of suntan lotion in Minnesota during that week Length of a student s hair and number of credits the student earned last year 50. Music and Grades. A couple of years ago a local newspaper published research results claiming a positive association between the number of years high school children had taken instrumental music lessons and their performances in school as measured by their GPA. 51. A group of parents then went to the school board demanding more funding for music programs as a way to improve student chances for academic success in high school. As a statistician, do you agree or disagree with their reasoning? Briefly explain.

11 Crawling. Researchers at the University of Denver Infant Study Center investigated whether babies take longer to learn to crawl in cold months (when they are often bundled in clothes that restrict their movement) than in warmer months. The study sought an association between babies first crawling age (in weeks) and the average temperature during the month they first try to crawl (about 6 months after birth). Between 1988 and 1991 parents reported the birth month and age at which their child was first able to creep or crawl a distance of four feet in one minute. Data were collected on 208 boys and 206 girls. The graph below plots average crawling ages (in weeks) against the mean temperatures when the babies were 6 months old. The researchers found a correlation of r = and their scatterplot was: 52. Draw the line of best fit on the graph. 53. Describe the association in context. 54. Explain, in context, what the slope of the line means.

12 55. Explain, in context, what the y-intercept of the line means. 56. Explain, in context, what the 2 R means. 57. In this context, what does a negative residual indicate?