Question: what is the difference between one tailed and two tailed?
Answer: A one-tailed test has the entire 5% of the alpha level in one tail (in either the left, or the right tail). A two-tailed test splits your alpha level in half (as in the image to the left). Let's say you're working with the standard alpha level of 5%. A two tailed test will have half of this (2.5%) in each tail.