correlation

Question 1

what is correlation

Answer 1

the degree to which scores on two variables relate

Question 2

what is the correlation coefficient

Answer 2

(r) provides an index to the extent to which two variables are correlated.

Question 3

how to work out r

Answer 3

Z = (X - µ) / SD

= observed value-mean
sd

r = ∑ZXZY
N
has a maximum value when Zx and Zy pairs are equal = N
has a minimum value when are equal but opposite signs = -N

Question 4

degrees of freedom

Answer 4

N-2

Question 5

how to report ?

Answer 5

There was a significant/ non significant, positive/ negative correlation between dv and iv, r(df)= , p=

Question 6

assumptions underlying pearsons correlation coefficient

Answer 6

1. the two variables must be on interval scales
2. the variables must be linearly related

if violated then use a non parametric test - Spearmans rho

Question 7

spearmans rho

Answer 7

can be used when the scatterplot indicates the relationship is monotonic but not linear
or when there is outliers

Question 8

reporting spearmans

Answer 8

due to the prescence of outliers….

there was a significant positive/ negative correlation Rs(df)= , p . such that

Question 9

what is a partial correlation ?

Answer 9

when you want to control for a third variable.

- measures the strength and direction of a relationship whilst controlling for a third variable.

Question 10

reporting partial correltaion

Answer 10

a partial correlation was conducted to test the strength of the relationship between IV and DV after controlling for VV.