A Brief Introduction to Biostatistics
c. jardin
(C. Jardin)
#1
One-tailed vs. two-tailed tests
- Two-side tests are conventionally used because
most of the time, we are not sure of the direction
of the difference
- One-tailed test are used only when we can
anticipate a priori the direction of a difference
- One-tailed tests are tempting because they are
more likely to give a significant result
- Given the same z-score, the P-value is halved for
one tailed test
- It also mean that they run a greater risk of
rejecting the Null Hypothesis when it is in fact
correct --- type I error