Two Sided
Two Sided
In t-tests, when do I used a two-sided as opposed to a one-sided?
I am trying to figure out why some of the problems use two-sided t-tests while some use one-sided t-test. How do you decided which one to use? Does two-sided mean you can have to outcomes such as the population increased or decreased while one-sided only tests whether the population increased (leaving out the idea that it could decrease)??
It is all down to the nature of the alternative hypothesis.
Do results either way better explain the situation than the null hypothesis or only results one way?
Examples will probably explain it better.
1. Does drug improve proportion of patients recovering from illness. Clearly only a higher proportion will validate use of the drug so this is a one-tailed test.
2. Last election 40% supported party A. Has proportion changed since then? Higher or lower results will confirm changed allegiance so this is a two-tailed test.
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