Over the past few days I’ve been analyzing data sets from some of the experiments I have conducted. It seems that the data I am generating is consistently not normal. This is caused by the design of the experiment. I have a cluster of data on the lowest end of the scale that indicates plants that have died during the experiment, then there is a normal distribution from the survivors. Here is an example:
Notice the spike on the far left (that’s the dead plants). I can make the data set look a little prettier (but far from clean) by generating a square root transformed data set.
No simple bell curves here. When I was planning my analyses I was thinking about parametric tests. Now I’m starting to set up SAS code for non-parametric tests.
So my data are not normal, they are extraordinary.