Suppose we have a situation (example given below) where there should be an effect in a certain direction (either greater or less than), but we are unsure of which direction applies to our sample.
Should two one tailed tests be used in such a situation, or one two tailed test?
- I ask because the two-tailed test has a larger critical value, so I imagine it would lead to more rejections.
Example: Suppose we have a population of animals, and we are measuring how many steps the animals are taking in a certain interval.
Also suppose that there are three types of animals:
- Normal animals, who take 100 steps in the interval
- lazy animals who take significantly less than 100 steps in the interval
- energetic animals, who take significantly more than 100 steps in the interval
Also, suppose that all our animals are one type (i.e. sample has either been drawn from a population of energetic, lazy or normal animals, but we don't know which one)
If we wanted to test whether our animals are from a normal, lazy, or energetic population, would we use a two tailed test or two one tailed tests?
- Our data is the number of steps each animal in the sample takes in the interval, and the null is that the number (or mean of it) should be 100
- Suppose the research question we want to answer is "Which type of population is our sample drawn from: Lazy, normal, or energetic
- I think in this case a 2 sides test would only be able to tell us whether or not our sample is from a normal population, but not which of Lazy/Energetic it is (if it is not normal). So for this we would need two one-sided tests, yes?