One- and Two-Tailed Tests
Answers
- Two-tailed tests look for an effect in either direction, so they compute two-tailed probabilities. They are much more common than one-tailed tests in scientific research because an outcome signifying that something other than chance is operating is usually worth noting. Some people disagree with the use of one-tailed tests except in very specific situations.
- Because you are interested in the effect in either direction, you will use a two-tailed test. Thus, the null hypothesis is that the mean of the seniors is equal to the mean of the freshmen.
- This question is asking you to compute a one-tailed probability. Using the binomial calculator with the values of
, and greater than or equal to 16, you get 
.
- This question is asking you to compute a two-tailed probability. The probability that it will come up heads 8 or fewer times is.0081. Multiply that by 2 and you get p =.0162.