I have a dataset that has three events: before, during and after. For each of these events there are five categories of rain: drought, dry, normal, wet and storm. For each of the categories there is a water level value. The water level data is non-parametric and the data is skewed. The categories are ordinal. What is the best test to use to look at the differences in medians within and between groups?
I have tried a friedman, but I don't know if it is the right test.
I'm using R.
This is an example of the data graphically. I'd like to see whether their is a significant difference within the categories (drought, dry etc.) and between the three events (before, during and after).
Do you mean something like this?