Quantitative Lecture 9

Question 1

What is correlation?

Answer 1

A standardised measure of the relationship between 2 variables.

Question 2

What questions can correlations answer?

Answer 2

1. Is change in one variable associated with a change in another variable?
2. Is an increase in one variable associated with an increase or decrease in another variable?
3. How strong is the relationship between variables?

Question 3

What is Pearson’s Product Moment Correlation?

Answer 3

A parametric test of relationships/associations that produces a correlation coefficient, or r.

Question 4

What does a greater r value indicate?

Answer 4

The stronger the relationship between the two variables.

Question 5

What is bivariate correlation?

Answer 5

The relationship between 2 variables.

Question 6

What are the generic assumptions for correlation?

Answer 6

1. Data must be at interval or ratio level.
2. Data must be normally distributed.
3. There should be no outliers/extreme scores.

Question 7

What are the specific assumptions for correlations?

Answer 7

1. There should be related pairs.
2. Linearity: there should be a linear relationship between the variables.

Question 8

What does assumption of linearity entail?

Answer 8

The variables should be linearly related, meaning a straight-line relationship between x and y.

Question 9

How can scatterplots be used in correlation?

Answer 9

Scatterplots can visually plot the relationship between two variables by assigning one variable to the x-axis and one to the y-axis.

Question 10

What does a positive direction of relationship indicate?

Answer 10

Higher scores on one variable tend to be associated with higher scores on another variable.

Question 11

What does a negative direction of relationship indicate?

Answer 11

Higher scores on one variable are associated with lower scores on another variable.

Question 12

What does a zero direction of relationship indicate?

Answer 12

There is no linear relationship between the two variables.

Question 13

What is the correlation coefficient (r)?

Answer 13

The strength of the relationship between 2 variables, lying between -1 and +1.

Question 14

What does a correlation coefficient of +1 indicate?

Answer 14

A perfect positive relationship.

Question 15

What does a correlation coefficient of -1 indicate?

Answer 15

A perfect negative relationship.

Question 16

What does a correlation coefficient of 0 indicate?

Answer 16

No linear relationship.

Question 17

What is the null hypothesis in correlation?

Answer 17

There is no relationship between the variables.

Question 18

What is the alternative hypothesis in correlation?

Answer 18

There is a relationship between the variables.

Question 19

What is common and shared variance in correlation?

Answer 19

The correlation coefficient (r) is a ratio between the covariance and a measure of the separate variances.

Question 20

What outputs can be found in SPSS for Pearson correlation?

Answer 20

1. Descriptive statistics
2. Correlations
3. Confidence intervals

Question 21

What should be included in formally reporting statistical results?

Answer 21

1. Type of correlation performed, variables correlated, and direction of relationship.
2. Test statistic, df, statistical significance.
3. Effect size (Cohen’s r).

Question 22

What is a caution regarding correlation?

Answer 22

Correlation does not inform us about an underlying causal link.

Question 23

What is the third variable problem?

Answer 23

There may be other measured or unmeasured variables that affect the results.

Question 24

What is partial correlation?

Answer 24

Calculates the relationship between 2 variables while controlling for the influence of additional variables.

Question 25

What must be met to perform a partial correlation?

Answer 25

The assumptions for correlation must also be met.