How to Determine a p-Value When Testing a Null Hypothesis

Click the link the skip to the situation you need to support or reject null hypothesis for:

That’s How to State the Null Hypothesis!

Hypotheses developers and testers usually hope that the null hypothesis is rejected and their alternative hypothesis supported – that the drug they’re testing is effective; the campaign they’re running is a success; that the light is bent by gravity as predicted by Newtonian physics and Einstein’s theory of relativity …

To find thevalue for your test statistic:

As in a jury trial, the burden of proof rests with the alternative hypothesis; innocent until proven guilty … When you test a hypothesis, you must act as judge and jury, but you are not the prosecutor.

When we were constructing confidence intervals, it mattered whether the data were drawn from normally distributed populations, whether the population standard deviations were equal, and whether the sample sizes were large or small, The answers to these questions helped us determine the proper multiplier for the standard error. The same considerations apply to significance tests. The answers determine the critical value of for a result to be declared statistically significant.

Null and Alternative Hypothesis | Real Statistics Using Excel

The null hypothesis can be thought of as a nullifiable hypothesis. That means you can nullify it, or reject it. What happens if you reject the null hypothesis? It gets replaced with the which is what you think might actually be true about a situation. For example, let’s say you think that a certain drug might be responsible for a spate of recent heart attacks. The drug company thinks the drug is safe. The null hypothesis is always the accepted hypothesis; in this example, the drug is on the market, people are using it, and it’s generally accepted to be safe. Therefore, the null hypothesis is that the drug is safe. The alternate hypothesis — the one you want to replace the null hypothesis, is that the drug isn’t safe. Rejecting the null hypothesis in this case means that you will have to prove that the drug is not safe.

Hypothesis testing - Handbook of Biological Statistics

The short answer is, as a scientist, you are required to; It’s part of the scientific process. Science uses a battery of processes to prove or disprove theories, making sure than any new hypothesis has no flaws. Including both a null and an alternate hypothesis is one safeguard to ensure your research isn’t flawed. Not including the null hypothesis in your research is considered very bad practice by the scientific community. If you set out to prove an alternate hypothesis without considering it, you are likely setting yourself up for failure. At a minimum, your experiment will likely not be taken seriously.


State the null hypothesis. When you state the null hypothesis, you also have to state the alternate hypothesis. Sometimes it is easier to state the alternate hypothesis first, because that’s the researcher’s thoughts about the experiment. (opens in a new window).

Steps in Statistical Hypothesis Testing

If (that is, ), we say the data are consistent with a population mean difference of 0 (because has the sort of value we expect to see when the population value is 0) or "we fail to reject the hypothesis that the population mean difference is 0". For example, if t were 0.76, we would fail reject the hypothesis that the population mean difference is 0 because we've observed a value of t that is unremarkable if the hypothesis were true.