Do you reject the null hypothesis if the p value is less?

As a statistical expert with extensive experience in data analysis and hypothesis testing, I often encounter questions about the interpretation of p-values and the decision-making process regarding the null hypothesis. The null hypothesis, often denoted as \( H_0 \), represents a statement of no effect or no difference, which is what we assume to be true before collecting data. The alternative hypothesis, denoted as \( H_1 \) or \( H_a \), represents the opposite of the null hypothesis, indicating an effect or a difference that we are testing for.
When conducting a hypothesis test, we calculate a p-value, which is the probability of observing a test statistic as extreme as, or more extreme than, the one calculated from my sample data, assuming that the null hypothesis is true. The p-value is a critical piece of information used to make a decision about the null hypothesis.
Step 1: **Compare your P-value to a predetermined significance level (α)**. This significance level is a threshold that you set before conducting the test to determine the strength of evidence required to reject the null hypothesis. Commonly used significance levels include 0.05, 0.01, and 0.001, although the choice of α depends on the context and the consequences of making a Type I error (rejecting a true null hypothesis).

Step 2: Make a decision based on the comparison. If the p-value is less than the significance level, it suggests that the observed data is unlikely if the null hypothesis were true, and you would typically reject the null hypothesis. Conversely, if the p-value is greater than or equal to the significance level, it indicates that the observed data is consistent with the null hypothesis, and you would typically fail to reject the null hypothesis.

Step 3: Consider the context and implications. The decision to reject or not reject the null hypothesis should be made with an understanding of the specific context and the potential impact of the decision. It's important to note that failing to reject the null hypothesis does not prove the null hypothesis to be true; it simply means that the data do not provide sufficient evidence to reject it.

Step 4: Report the results. When reporting the results of a hypothesis test, it is important to include the test statistic, the p-value, the significance level used, and the conclusion regarding the null hypothesis.

Now, let's apply these steps to the scenario you provided:

- The p-value is given as 0.003.
- The commonly used significance level is 0.05.

Given that the p-value (0.003) is less than the significance level (0.05), we have enough evidence to reject the null hypothesis. This means that, according to the data and the chosen significance level, there is a statistically significant effect or difference that we can observe.

**

Step 6: Compare your P-value to --. ... If the P-value is less, reject the null hypothesis. If the P-value is more, keep the null hypothesis. 0.003 < 0.05, so we have enough evidence to reject the null hypothesis and accept the claim.Oct 17, 2009