Module 4 Review Questions

Module 4 Review Questions Answer the following multiple choice questions: 1. Suppose the correlation between two variables x and y is due, in part, to the fact that y is 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 the above. 2. Which of the following statements are true? I. Regression outliers, if removed, cause a dramatic change in the slope and orientation of the least squares line. II. Determining a conditional distribution for a two-way table consists of calculating percents for either the row or column sums. III. An influential observation can have a strong effect on both the regression line and the correlation between the X and Y variables. (a) I and II only (b) I and III only (c) II and III only (d) I, II, and III (e) None of the above. 3. 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 the above. 4. Suppose that the scatterplot of log Y on X produces a correlation close to 1. Which of the following is true? I. The correlation between the variables X and Y will also be close to 1. II. The residual plot of Y on X will show a clearly curved pattern of points. III. The difference between consecutive values of y for equal x-intervals is approximately constant. (a) I and II only (b) II only (c) II and III only (d) I, II, and III (e) None of the above. 5. Which of the following are true statements? I. High correlation does not necessarily imply causation. II. A lurking variable is a name given to a variable that was not considered in an experimental design, but had an effect on the response variable. 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 the above. 6. There is a positive association between the number of drownings and ice cream sales. This is an example of an association likely caused by: (a) Coincidence (b) Cause and effect relationship (c) Common response (d) Confounding factor (e) None of the above 7. 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. 8. A study examined the relationship between the sepal length and sepal width for two varieties of an exotic tropical plant. Varieties A and 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. 9. From tax records, it is relative easy to determine the amount of liquor consumed per capita and the number of cigarettes consumed per capita for each of the 10 provinces of Canada. These are plotted on a scatterplot and a high positive correlation is found. Which of the following is correct? (a) This implies that heavy smoking causes people to drink more. (b) This implies that heavy drinking causes people to smoke more. (c) We cannot conclude cause and effect, but this also implies that there is a high positive correlation between cigarette smoking and alcohol consumption for individuals. (d) This could be an example of a correlation caused by a common response if both activities are highly correlated with average family income and average income varies widely among the provinces. (e) We can conclude cause and effect, and it is likely that the same individuals both smoke and consume liquor. 10. Which of the following is true? (a) log(AB) = logAlogB. (b) log(A+B) = logA + logB. (c) log(A/B) = logA – logB. (d) log(A-B)=logA-logB (e) All of the above. Answers: 1. b 2. e, only Statement III is true 3. c 4. b 5. d 6. c 7. d 8. d 9. d 10. c