Correlations Flashcards
What can associations between 2 variables be characterised by?
direction
strength
shape
How do you visualise correlation data?
by using scatter plots
shows strength of correlation and line of best fit
What shapes can you get for a correlation?
linear
U-shaped
Inverted U-shaped
What is a correlation coefficient?
descriptive statistics that describe an association between 2 variables
What are the 2 types of correlation coefficients?
Pearson product-moment correlation
Spearman rank correlation
describe strength and direction of a linear association
What is Pearson’s correlation used for?
interval and ratio data that is normally distributed
What is Spearman’s correlation used for?
ordinal data or interval/ratio data that is not normally distributed
uses ranks instead of raw data
What is a -1 association?
a perfect negative linear association
What is a 0 association?
no linear association
What is +1 association?
a perfect positive linear association
How do you calculate Spearman correlation?
1- transforming raw values into ranks on both variables
e.g smallest value gets ‘0’ then next value gets ‘1’
2- calculate pearsons correlation between ranked variables
What if there’s 2 scores of the same number?
assign an average rank
If the p-value is below 0.5 what does that mean?
test is significant and you reject null hypothesis
If the value is above 0.5 what does that mean?
test is not significance and you accept null hypothesis
What does e-05 mean?
Means p<0.5, significant
