![]() ![]() If you've taken calculus, you may already know what needs to be done: The area under a curve is the integral of the function that defines the curve. ![]() Since the distribution is symmetrical, you can simply double that value to get the two-tailed p-value. So in order to calculate the p value that corresponds to a particular t-statistic at some degrees of freedom, you need to measure the area under the curve from that point on out. ![]() The p value is simply the proportion of the distribution - the area under the curve - that is at least as far from 0 as your t-statistic. way out in one of the tails), the you conclude that it is unlikely to have come from the null distribution. That mens you can compare that t-statistic to the rest of its null distribution - if it's a very unusual value for that distribution (i.e. So as long as you know how many degrees of freedom you have, you know theoretically what distribution your t-statistic came from under the null hypothesis. There is a defined theoretical distribution of t-statistics (the t distribution). If you want a one-tailed p value, then it's what proportion of t-statistics (for those degrees of freedom) are that high or higher (for the positive tail) or that low or lower (for the negative tail). The p value in a t-test (any t-test, not just two independent samples) refers to what proportion of t-statistics (for those degrees of freedom) are that extreme or more, assuming you want a two-tailed p value. First, a little background on the meaning of a p value ![]()
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