Week 7

Question 1

What is correlation?

Answer 1

Correlation quantifies the degree of association between two variables (bivariate analysis)

Question 2

What does r stand for, and what are 3 important values of it?

Answer 2

r = coefficient of correlation
r=1 - perfect positive linear relationship
r=-1 - perfect negative linear relationship
r=0 - no correlation

Question 3

What is a perfect correlation?

Answer 3

When the line of best for goes through every point (gradient is irrelevant)

Question 4

Sxx/Syy/Sxy?

Answer 4

Sxx = Σx^2 - ((Σx)^2)/n

Sxy = Σxy - (Σx.Σy)/n

Question 5

Correlation equation?

Answer 5

r = Sxy/(Sxx.Syy)^0.5

Question 6

What is spurious correlation?

Answer 6

‘By chance’ correlation

Question 7

Steps for testing significance of correlation?

Answer 7

1) set hypotheses: H0: p=0 H1: p not equal to zero
2) choose significance level
3) select test statistic (t-dist.)
4) decision rule (reject H0 if |tobt.|>|tcrit.|
5) compute answer:

Use n-2 DofF

t = (r(n-2)^0.5) / (1-r^2)^0.5

Question 8

Degrees of freedom for t test when testing significance of correlation?

Answer 8

n-2