## one-sided vs. two-sided hypothesis test (exp?) - …

In keeping with Tukey's comment, tests of the null hypothesis that two population means or proportions are equal are almost always two-sided (or two-tailed^{*}).

[onesided test]

Is the pizza you ordered from the pizza service well done (it couldbe raw, or burnt, or well done) [two sided test]

Generally speaking, we base the decision on the value of a teststatistic, e.g.

## Two sided hypothesis test calculator

If a one-sided analysis had been proposed for the trial, these results would have been ignored on the grounds that they were the result of unlikely random variability under a hypothesis of no difference between beta-carotene and placebo.