correlational analysis

positive association

negative association

strong association

weak association

correlation coefficients

descriptive statistics that describe an association between variables

Pearson’s product-moment correlation

• Describes linear associations between variables

• Used for interval/ratio level data that is normally distributed

• -1 is a perfect negative linear association

• 0 no linear association

• +1 perfect positive linear association

Spearman’s rank correlation

• Describes linear associations between variables

• Used for ordinal level data or interval/ratio data that is skewed

• Uses ranks instead of raw data values

• 1 = perfect negative correlation

• 0 = no correlation

• +1 = perfect positive correlation)

reporting a correlation test

_{^{R= Spearman’s and Pearson’s are always denoted as r}}

_{^{Rs= tells us this is a Spearman’s correlation}}

_{^{(33) = degrees of freedom (n-2)}}

_{^{.62 correlation coefficients to a maximum of 3 d.p}}

How to report a Spearman’s/Pearson’s correlation coefficient

Spearman’s/ Pearson’s correlation was computed to assess the relationship between [variable 1] and [variable 2]. There was a [negative or positive] correlation between the two variables r(degrees of freedom) = the r statistic, p = p value.