PSYC*1010 Chapter 15: Correlation

Question 1

What is correlation?

Answer 1

A statistical technique used to measure and describe the relationship between two variables

Question 2

How many scores are required from each participant when computing correlation?

Answer 2

Two (one from each variable)

Question 3

T or F: There is no attempt to manipulate or control variables in a correlation study.

Answer 3

True

Question 4

What does the sign (+/-) of a correlation indicate?

Answer 4

The direction of the relationship

Question 5

What is a positive correlation?

Answer 5

A correlation where two variables tend to change in the same direction

Question 6

What is a negative correlation?

Answer 6

A correlation where two variables tend to change in opposite directions

Question 7

T of F: The direction of a correlation is related to its strength.

Answer 7

False

Question 8

What is the most common use of correlation?

Answer 8

To measure straight-line/linear relationships

Question 9

What does the numerical value of a correlation indicate?

Answer 9

The strength/consistency of a correlational relationship

Question 10

What is a perfect correlation?

Answer 10

A relationship where the actual data points perfectly fit the specific form being measured

Question 11

What does a correlation of 1.00 indicate?

Answer 11

A perfect correlation

Question 12

What does a correlation of 0 indicate?

Answer 12

No consistency between variables

Question 13

What does the Pearson correlation measure?

Answer 13

The degree and direction of the liner relationship between two variables

Question 14

What is the notation for the Pearson correlation of a sample?

Answer 14

r

Question 15

What is the notation for the Pearson correlation of the population?

Answer 15

rho (ρ)

Question 16

How is the Pearson correlation computed?

Answer 16

By dividing the covariability of X and Y by the variability of X and Y together

Question 17

What is covariability?

Answer 17

The degree to which two variables vary together

Question 18

What does the sum of products of deviations measure?

Answer 18

The degree of covariability between two variables

Question 19

What notation is used to describe the sum of products of deviations

Answer 19

SP

Question 20

When using a table to calculate SP and the Pearson correlation, what are the headings of each column?

Answer 20

X, Y, (X-M_X), (Y-M_Y), (X-M_X)^2, (Y-M_Y)^2, (X-M_X)(Y-M_Y)

Question 21

What happens when a constant value is added or subtracted from each X value?

Answer 21

The pattern of data points would shift to the right or left, but correlation stays the same

Question 22

What happens when a constant value is added or subtracted from each Y value?

Answer 22

The pattern of data points would shift up or down, but correlation stays the same

Question 23

What happens when each X or Y value is multiplied or divided by a constant positive?

Answer 23

Neither the pattern nor the correlation change

Question 24

What happens when each X or Y value is multiplied or divided by a constant negative?

Answer 24

A mirror image of the original pattern is produced and the sign of the correlation changes, but the numerical value doesn’t

Question 25

What is regression?

Answer 25

The process of using relationships to make predictions

Question 26

What is a common technique for demonstrating validity?

Answer 26

Correlation

Question 27

T or F: Correlations can't be used to help measure and describe reliability.

Answer 27

False. They can.

Question 28

In terms of correlation, what indicates a good level of reliability?

Answer 28

A strong positive correlation

Question 29

In terms of correlation, what indicates poor reliability?

Answer 29

A weak correlation

Question 30

If a measurement procedure produces stable and constant measurements, what is it considered to be?

Answer 30

Reliable

Question 31

T or F: The prediction of a theory could be tested by determining the correlation between two variables.

Answer 31

True

Question 32

What are four considerations to bear in mind when encountering a correlation?

Answer 32

- Correlation is not proof of a cause-and-effect relationship - The value of a correlation can be greatly affected by the range of scores in the data - One or two outliers can have a dramatic effect on the value of a correlation - Correlation shouldn't be interpreted as a proportion

Question 33

What is the most common error in interpreting correlations?

Answer 33

Assuming that a correlation necessarily implies a cause-and-effect relationship

Question 34

What is needed to establish a cause-and-effect relationship?

Answer 34

A true experiment being conducted

Question 35

T or F: The correlation within a restricted range could be completely different from the correlation obtained from a full range.

Answer 35

True

Question 36

What is an outlier?

Answer 36

An individual with X and/or Y values that are substantially different from the values obtained for the other individuals in the data set

Question 37

What is the correlation of determination?

Answer 37

The effect size of a correlation

Question 38

What does the correlation of determination measure?

Answer 38

How much of the variance in one variable can be determined from its relationship with the other variable

Question 39

What is the notation for the correlation of determination?

Answer 39

r^2

Question 40

What does an r^2 value of 0.01 to 0.08 indicate?

Answer 40

A small effect

Question 41

What does an r^2 value of 0.09-0.24 indicate?

Answer 41

A medium effect

Question 42

What does an r^2 value of 0.25 or greater indicate?

Answer 42

A large effect size

Question 43

What does "regression toward the mean" refer to?

Answer 43

The fact that when there is a less-than-perfect correlation between two variables, extreme scores (high or low) for one variable tend to be paired with less extreme scores (closer to mean) on the second variable

Question 44

What are the null and alternate hypotheses for a two-tailed correlation test?

Answer 44

H0: ρ = 0 (no population correlation) H1: ρ ≠ 0 (population correlation present)

Question 45

What are the null and alternate hypotheses for a one-tailed correlation test predicting a positive relationship?

Answer 45

H0: ρ ≤ 0 (population correlation not positive) H1: ρ > 0 (population correlation positive)

Question 46

What are the null and alternate hypotheses for a one-tailed correlation test predicting a negative relationship?

Answer 46

H0: ρ ≥ 0 (population correlation not negative) H1: ρ < 0 (population correlation negative)

Question 47

When a nonzero correlation is obtained from a sample, what are the two interpretations the hypothesis must decide between?

Answer 47

- There is no correlation in the population and the sample value is the result of sampling error (H0) - The nonzero sample correlation accurately represents the nonzero correlation in the population (H1)

Question 48

How are degrees of freedom calculated for correlations?

Answer 48

df= n-2