lecture 7- correlational analysis

What is a scatterplot?

Describes the associations between 2 variables.

An association can be characterised by its

• direction - positive/negative

• Strength- strong/weak/no association

• Shape- linear (most common), u-shaped, inverted u-shaped

What are correlation coefficients? Give 2 examples.

Descriptive stats that describe an association between variables.

• pearson product-moment correlation

• Spearman rank correlation

What is pearson’s correlation?

• Denoted as r

• describes linear associations between variables

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

• -1 = perfect negative linear association

• 0 = no linear association

• +1 = perfect positive association

What is spearman’s correlation?

• Denoted as r

• 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 = negative, 0= no correlation, +1 = positive correlation

How do you report a correlation test?

“ A spearman’s/pearson’s correlation analysis showed that was/wasn’t a significant positive/negative correlation between FOMO and the number of drinking establishments attended, rs(33)=.62, p<.001.”|

What are degrees of freedom?

A number that tells you about the sample size and the specific test conducted.

A number of pieces of info that are free to vary when computing stats.

Usually a bit smaller than number of observations. (N-2)

What do you do if you want to conduct one-tailed test but only have p value from two-tailed test?

Divide p value by 2.