Maths and Stats Support

Use: Comparing the mean difference of three or more measurements of the same continuous variable.  You should have measurements in different columns with each row representing one subject.

Dependent (outcome) variable: Continuous
Independent (predictor) variable: 3+ categories e.g. weight measured at three time points or three types of biscuit 

Example: testing for a change in weight on a diet at three or more time points or comparing taste scores for 3+ different biscuits

Summary statistics/graphs: Summarise the means at each time point and a mean bar or line chart 

Use: Testing for a difference between 3+ measurements of the same variable when the variable of interest is ordinal or the dependent variable is very skewed.

Dependent (Outcome): Ordinal or skewed repeated measures
Independent (predictor): 3+ time points or conditions

Example: Each person tries three different biscuits and gives a taste rating from disgusting to delicious or weight on a diet is very skewed 

The Friedman test can also be used when you have asked people to rank a list of options and wish to see if there are general preferences

Summary statistics/graphs: Use medians, Interquartile range and boxplot for ordinal or skewed data.   

Note: If you have taken the mean or sum of several ordered questions (scale mean), use parametric tests such as t-tests. Some disciplines use parametric tests for individual ordinal questions but a wider range of responses (ideally 7+) is needed