STAT 1350, Quiz #10, Summer 2014 Name _______________________________________

1-3. A random sample of patients who attended a clinic was selected. The age of the patient (years) and the number of days since the last visit were collected and are displayed in the figure below. The least-squares regression line for predicting number of days since the last visit from the age of the patient is y = 600.081 – 8.694x.

1. The slope of this line is
A) 600.081. B) 8.694. C) –8.694. D) 600.081 – 8.694 = 591.387.
Ans: C

2. The slope of this line tells us the
A) correlation between age of patient and days since last visit.
B) change in days since last visit for each year older a patient is, on average.
C) change in the age of the patient for each extra day since the last visit.
D) average days since last visit for all of the patients.
Ans: B

3. Using this line, you predict that the number of days since last visit to the clinic for a 50-year-old patient will be about
A) 63 days. B) 78 days. C) 165 days. D) 200 days. E) 252 days.
Ans: C

4. What can we say about the relationship between a correlation r and the slope b of the least-squares line for the same set of data?
A) r is always larger than b.
B) r and b always have the same sign (+ or –).
C) b is always larger than r.
D) b and r are measured in the same units.
E) Both C and D are correct.
Ans: B

5. A study of 3617 adults found that those who attend religious services live longer (on the average) than those who don’t. Is this good evidence that attending services causes longer life?
A) Yes, because the study is an experiment.
B) No, because religious people may differ from non-religious people in other ways, such as smoking and drinking, that affect life span.
C) Yes, because the sample is so large that the margin of error will be quite small.
D) No, because we can’t generalize from 3617 people to the millions of adults in the country.
Ans: B

6. If the least-squares regression line for predicting y from x is y = 500 – 20x, what is the predicted value of y when x = 10?
A) 300 B) 500 C) 4800 D) 700 E) 20
Ans: A

7. Perfect correlation means all of the following except
A) r = –1 or r = +1.
B) all points on the scatterplot lie on a straight line.
C) all variation in one variable is explained by variation in the other variable.
D) there is a causal relationship between the variables.
E) each variable is a perfect predictor of the other.
Ans: D

8. The correlation coefficient for these data is r = 0.45. Which of the following statements is true?
A) Predictions using this equation will be fairly poor since about 45% of the variation in price can be explained by the linear relationship with number of pages.
B) Predictions using this equation will be fairly good since about 45% of the variation in price can be explained by the linear relationship with number of pages.
C) Predictions using this equation will be fairly poor since about 20% of the variation in price can be explained by the linear relationship with number of pages.
D) Predictions using this equation will be fairly good since about 20% of the variation in price can be explained by the linear relationship with number of pages.
Ans: C

9. The best way to settle questions of causation is
A) a careful observational study. D) to draw a line graph.
B) a properly designed experiment. E) to calculate a correlation.
C) to draw a scatterplot.
Ans: B