Using P-values to make conclusions
Using P-values to make conclusions
Learn how to use a P-value and the significance level to make a conclusion in a significance test.
This article was designed to provide a bit of teaching and a whole lot of practice. The questions are ordered to build your understanding as you go, so it's probably best to do them in order. Onward!
We use p-values to make conclusions in significance testing. More specifically, we compare the p-value to a significance level alpha to make conclusions about our hypotheses.
If the p-value is lower than the significance level we chose, then we reject the null hypotheses H, start subscript, 0, end subscript in favor of the alternative hypothesis H, start subscript, start text, a, end text, end subscript. If the p-value is greater than or equal to the significance level, then we fail to reject the null hypothesis H, start subscript, 0, end subscript—this doesn't mean we accept H, start subscript, 0, end subscript. To summarize:
Let's try a few examples where we use p-values to make conclusions.
Example 1
Alessandra designed an experiment where subjects tasted water from four different cups and attempted to identify which cup contained bottled water. Each subject was given three cups that contained regular tap water and one cup that contained bottled water (the order was randomized). She wanted to test if the subjects could do better than simply guessing when identifying the bottled water.
Her hypotheses were H, start subscript, 0, end subscript, colon, p, equals, 0, point, 25 vs. H, start subscript, start text, a, end text, end subscript, colon, p, is greater than, 0, point, 25 (where p is the true likelihood of these subjects identifying the bottled water).
The experiment showed that 20 of the 60 subjects correctly identified the bottle water. Alessandra calculated that the statistic p, with, hat, on top, equals, start fraction, 20, divided by, 60, end fraction, equals, 0, point, 3, with, \bar, on top had an associated P-value of approximately 0, point, 068.
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