Activity Type Title

Chapter 1. Chapter

Infographic

Scientific American: Psychology

Infographic Activity 1.4: The Correlation Coefficient

The Correlation Coefficient: What’s in a Number?

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A correlation indicates a relationship between two variables, such as the amount of time you spend studying and the grade you get on a test. This relationship is often indicated using a correlation coefficient, symbolized as r. To interpret the relationship using a correlation coefficient (r), ask yourself two questions:

(1) What is the direction of the relationship?

(2) What is the strength of the relationship?

A scatterplot helps us see what the correlation looks like. And remember, a correlation between two variables does not necessarily mean the one variable caused the change in the other variable.

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1.1 Quiz

1. What kind of visual representation would be the most useful for showing the correlation that exists between two variables?

A histogram

A bar graph

A pie chart

A scatterplot

Correct.

Incorrect.

2. While trying to determine the relationship between the temperature outside and the number of flies that she sees in her house, Mary makes observations of both factors for several weeks. She then computes a correlation coefficient. Which part of that coefficient will tell Mary the strength of the relationship between the two variables?

The sign in the coefficient

The number in the coefficient

The number of observations used to calculate the coefficient

The internal validity of the coefficient

Correct.

Incorrect.

3. Christopher is taking an exam in his psychology course, and the question asks him to interpret a correlation coefficient. The coefficient in his question is statistically possible. Which of the following numbers could not be the coefficient in question?

-1.21

0.79

0.00

-0.43

Correct.

Incorrect.

4. Why is it that psychologists cannot state that a correlation between two variables indicates that a change in one causes a change in the other?

Because correlation coefficients are unrelated to the change, or movement, in variables. Correlations can only occur when the variables are constant

Because correlations only involve experimental studies which involve manipulation of variables.

Because a third variable may have influence on the results

Because only very strong correlations – around 0.75 and above – can be used to determine cause and effect, and not all correlations exceed that level.

Correct.

Incorrect.

5. The more Brandon cleans his kitchen, the less dirt he sees on the counters and floor. In this example, the correlation between the variables “amount of cleaning” and “amount of dirt” would be best described by which of the following coefficients?

+0.91

+0.14

-0.79

-2.31

Correct.

Incorrect.

6. A correlation coefficient is usually indicated by the symbol _____.

Correct.

Incorrect.

7. In a graphical depiction of a perfect negative correlation, which of the following shapes would you be most likely to see?

An oval that is higher than it is wide

A diagonal line that moves from the top left to the bottom right

A diagonal line that moves from the bottom left to the top right

An oval that is wider than it is high

Correct.

Incorrect.

8. The relationship between the number of alcoholic beverages one can consume without becoming intoxicated and their hair color would probably be best described by which of the following correlation coefficients?

-0.56

0.90

-0.02

0.47

Correct.

Incorrect.