Correlation

Question 1

What are the parametric and non parametric tests for a relationship?

Answer 1

Pearsons correlation for parametric

Spearman’s rank correlation for non parametric

Question 2

What does a positive and negative correlation represent?

Answer 2

positive - both variables increase

negative - one variable increases as another decreases

Question 3

What are the assumptions to carry out a Pearsons test?

Answer 3

• normal distribution
• interval / ratio level
• Linear relationship

Question 4

What are the assumptions to carry out a spearmans test?

Answer 4

• ordinal, ratio or interval level data

- Monotonic relationship

Question 5

What is a monotonic relationship?

Answer 5

its a relationship that increase or decrease but not in a linear fashion

Question 6

what is covariance?

Answer 6

• if two variables are related, when one variable deviates from its mean we would expect the other variable to deviate from its mean in a similar way
• measure of joint variability of two variables

Question 7

what is the influence of sample size on R volume?

Answer 7

• sample size might increase the r volume

- large the sample the smaller the r volume is needed for a significant difference

Question 8

according to Cohen what is a weak, medium, strong and very strong correlation?

Answer 8

small - 0.3
medium - 0.3-0.5
Strong - 0.5-0.9
very strong - 0.9-1

Question 9

according to Evan what is a very weak through to a very strong correlation?

Answer 9

very weak - 0.19
weak - 0.2-0.39
moderate - 0.4-0.59
strong - 0.6-0.79
very strong - 0.8-1

Question 10

How relationships may arise provide three ways?

Answer 10

• x causes y
• y causes x
• coincidence
• confounding
• correlation induced by a third variable
• time

Question 11

what are some cautions with correlations?

Answer 11

• outlying results may affect correlation
• R = 0 doesn’t always mean no relationship
• hidden sub groups
• correlation is not causation