For example, how would you decide between which tailed test to do in the following experiment:
Ethanol dilutions were made with different proportions and Daphnias were submerged in them to collect their heart rates. The Daphnias were also submerged into beakers with different temperatures.
My null hypothesis was that the Daphnia will not be affected by the changing variables and if they are, it is due to a purely kinesis response (caused by chance).
My alternative hypothesis was that Ethanol would decrease the heart rates of the Daphnias as the dilution concentrations increase. I assumed this because Ethanol is a respiratory and nervous system depressant that acts as an anesthetic and potentially leads to death after an overdose. I also assumed that the Daphnias' heart rates would fall and become steadier in lower temperatures because they usually inhabit cooler, freshwater habitats.