Results: An example is given from an experiment where rats were randomly assigned to receive
either 0, 60, 180, or 240 mg/L of fluoxetine in their drinking water, with performance on the forced
swim test as the outcome measure. Dose was treated as either a categorical or continuous variable
during analysis, with the latter analysis leading to a more powerful test (p = 0.021 vs. p = 0.159).
This will be true in general, and the reasons for this are discussed.