# STAT 213 Chapter Notes - Chapter 9: Scatter Plot, Absorbance, Supermodel

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Published on 24 Jun 2019

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Chapter 8: Simple Linear Regression

1. Explain what each correlation coefficient means.

a. r = 0.1

b. r = - 0.15

c. r = - 1.0

d. r = 0.92

2. Match the correlation coefficients with their scatterplots. Select

the letter of the scatterplot below which corresponds to the

correlation coefficient.

a. r = -0.74

b. r = 0.22

c. r = 0.89

d. r = -0.49

Chapter 8: Simple Linear Regression

3. Keeping water supplies clean requires regular measurement of

levels of pollutants. The measurements are indirect- a typical

analysis involves forming a dye by a chemical reaction with the

dissolved pollutant, then passing light through the solution and

measuring its " absorbance." To calibrate such measurements, the

laboratory measures known standard solutions and uses regression

to relate absorbance and pollutant concentration. This is usually

done every day. Here is one series of data on the absorbance for

different levels of nitrates. Nitrates are measured in milligrams

per liter of water.

Chemical theory says that these data should lie on a straight line. If

the correlation is not at least 0.997, something went wrong and the

calibration procedure is repeated.

a. Find the correlation!r

b. Must the calibration be done again? (Answer YES or NO).!

Nitrates

75

50

125

300

300

300

800

1000

1800

2900

Absorbance

6.6

7.5

11

28.8

47.8

95.1

141.5

199.4

219.8

239.2

Chapter 8: Simple Linear Regression

4. What are all the values that a correlation!r!can possibly take?!

5. You have data for many years on the average price of a barrel of

oil and the average retail price of a gallon of unleaded regular

gasoline. When you make a scatterplot, the explanatory variable on

the!x!-axis:!

6. In a scatterplot of the average price of a barrel of oil and the

average retail price of a gallon of gasoline, you expect to see:

7. A researcher wishes to determine whether the rate of water flow

(in liters per second) over an experimental soil bed can be used

to predict the amount of soil washed away (in kilograms). In this

study, the explanatory variable is the:

8. A researcher measures the correlation between two variables. This

correlation tells us!

9. The Columbus Zoo conducts a study to determine whether a

household's income can be used to predict the amount of money the

household will give to the zoo's annual fund drive. The response

variable in this study is!