A p-value is a measure of the probability that an observed difference could have occurred just by random chance. The lower the p-value, the greater the statistical significance of the observed difference. P-value can be used as an alternative to or in addition to pre-selected confidence levels for hypothesis testing.
1. P-value is the chance that say out of 1000 repetitions of the same experiment, how many times we get the exact same sample data that we have obtained in this specific sample. 2. More extreme term refers to the magnitude of the sample statistic of interest, for example, if the statistic of interest is sample mean , then more extreme here will ...
Jul 06, 2021 · The p -value is a number between 0 and 1 and interpreted in the following way: A small p -value (typically ≤ 0.05) indicates strong evidence against the null hypothesis, so you reject the null hypothesis. A large p -value (> 0.05) indicates weak evidence against the null hypothesis, so you fail to reject the null hypothesis.
The P -value approach involves determining "likely" or "unlikely" by determining the probability — assuming the null hypothesis were true — of observing a more extreme test statistic in the direction of the alternative hypothesis than the one observed. If the P -value is small, say less than (or equal to) α, then it is "unlikely."
A p-value is the probability of seeing a simple statistic value as extreme or more extreme than the one observed in the sample, if the null hypothesis is true. A small p-value provides what kind of evidence against the null?
Specifically, the four steps involved in using the P -value approach to conducting any hypothesis test are: 1 Specify the null and alternative hypotheses. 2 Using the sample data and assuming the null hypothesis is true, calculate the value of the test statistic. Again, to conduct the hypothesis test for the population mean μ, we use the t -statistic t ∗ = x ¯ − μ s / n which follows a t -distribution with n - 1 degrees of freedom. 3 Using the known distribution of the test statistic, calculate the P-value: "If the null hypothesis is true, what is the probability that we'd observe a more extreme test statistic in the direction of the alternative hypothesis than we did?" (Note how this question is equivalent to the question answered in criminal trials: "If the defendant is innocent, what is the chance that we'd observe such extreme criminal evidence?") 4 Set the significance level, α, the probability of making a Type I error to be small — 0.01, 0.05, or 0.10. Compare the P -value to α. If the P -value is less than (or equal to) α, reject the null hypothesis in favor of the alternative hypothesis. If the P -value is greater than α, do not reject the null hypothesis.
The P -value, 0.0127, tells us it is "unlikely" that we would observe such an extreme test statistic t * in the direction of HA if the null hypothesis were true. Therefore, our initial assumption that the null hypothesis is true must be incorrect. That is, since the P -value, 0.0127, is less than α = 0.05, we reject the null hypothesis H0 : μ = 3 in favor of the alternative hypothesis HA : μ < 3.
The P -value for conducting the right-tailed test H0 : μ = 3 versus HA : μ > 3 is the probability that we would observe a test statistic greater than t * = 2.5 if the population mean μ really were 3. Recall that probability equals the area under the probability curve. The P -value is therefore the area under a tn - 1 = t14 curve and to the right of the test statistic t * = 2.5. It can be shown using statistical software that the P -value is 0.0127. The graph depicts this visually.
If the P -value is less than (or equal to) α, reject the null hypothesis in favor of the alternative hypothesis. If the P -value is greater than α, do not reject the null hypothesis.
Again, to conduct the hypothesis test for the population mean μ, we use the t -statistic t ∗ = x ¯ − μ s / n which follows a t -distribution with n - 1 degrees of freedom.
A nice definition of p-value is "the probability of observing a test statistic at least as large as the one calculated assuming the null hypothesis is true". The problem with that is that it requires an understanding of "test statistic" and "null hypothesis". But, that's easy to get across.
Therefore, a p -value of 0.06 would mean that if we were to repeat our experiment many, many times (each time we select 100 students at random and compute the sample mean) then 6 times out of 100 we can expect to see a sample mean greater than or equal to 5 ft 9 inches.
The p-value is the area of the shaded region under the null histogram: it is the chance, assuming the null is true, of observing an outcome whose likelihood ratios tend to be large regardless of which alternative happens to be true. In particular, this construction depends intimately on the alternative hypothesis.
An important consideration is what do we class as a "small" probability? What's the cutoff point at which we're willing to say that an event is unlikely? The standard benchmark is 5% (0.05) and this is called the significance level. When the p-value is smaller than the significance level we reject the null hypothesis as being false and accept our alternative hypothesis. It is common parlance to claim a result is "significant" when the p-value is smaller than the significance level i.e. when the probability of what we observed occurring given the null hypothesis is true is smaller than our cutoff point. It is important to be clear that using 5% is completely subjective (as is using the other common significance levels of 1% and 10%).
The traditional way to choose between (A) and (B) is to choose an arbitrary cut-off for p. We choose (A) if p > 0.05 and (B) if p < 0.05.