## How to Set Up a Hypothesis Test: Null versus Alternative

### Null Hypothesis (1 of 4) - David Lane

Let me expand on the previous paragraph byquoting avery important passage from Edgington (1986). "Justas thereference set (read as "sampling distribution"for now) ofdata permutations is independent of the test statistics,so is thenull hypothesis. A difference between means may be used asa teststatistic, but the null hypothesis does not refer to adifferencebetween means. The null hypothesis, no matter what teststatistic isused, is that there is no differential effect of thetreatments forany of the subjects. ... Thus the alternative hypothesisis that themeasurement of at least one subject would have beendifferent underone of the other treatment conditions. Inferences aboutmeans must bebased on nonstatistical considerations; the randomizationtest doesnot justify them." (p. 531)

### The null hypothesis is an hypothesis about a population parameter

Not so long ago, people believed that the world was flat.

Null hypothesis, H_{0}: The world is flat.

Alternate hypothesis: The world is round.

Several scientists, including , set out to disprove the null hypothesis. This eventually led to the rejection of the null and the acceptance of the alternate. Most people accepted it — the ones that didn’t created the !. What would have happened if Copernicus had not disproved the it and merely proved the alternate? No one would have listened to him. In order to change people’s thinking, he first had to prove that their thinking was *wrong*.

Before actually conducting a hypothesis test, you have to put two possible hypotheses on the table — the null hypothesis is one of them. But, if the null hypothesis is rejected (that is, there was sufficient evidence against it), what’s your alternative going to be? Actually, three possibilities exist for the second (or alternative) hypothesis, denoted H_{a}. Here they are, along with their shorthand notations in the context of the pie example:

## Support or Reject Null Hypothesis in Easy Steps

Typically in a hypothesis test, the claim being made is about a population (one number that characterizes the entire population). Because parameters tend to be unknown quantities, everyone wants to make claims about what their values may be. For example, the claim that 25% (or 0.25) of all women have varicose veins is a claim about the proportion (that’s the ) of all women (that’s the ) who have varicose veins (that’s the — having or not having varicose veins).

## Explainer: what is a null hypothesis? - The Conversation

When you set up a hypothesis test to determine the validity of a statistical claim, you need to define both a null hypothesis and an alternative hypothesis.

## 5 Differences between Null and Alternative Hypothesis …

You need descriptive statistics for three reasons. First, if you don’t have enough variance on the variables of interest, you can’t test your null hypothesis. If everyone is white or no one is obese, you don’t have the right dataset for your study. Second, you are going to need to include a table of sample statistics in your paper. This should include standard demographic variables – age, sex, education, income and race are the main ones. Last, and not necessarily least, descriptive statistics will give you some insight into how your data are coded and distributed.

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

In the second experiment, you are going to put human volunteers with high blood pressure on a strict low-salt diet and see how much their blood pressure goes down. Everyone will be confined to a hospital for a month and fed either a normal diet, or the same foods with half as much salt. For this experiment, you wouldn't be very interested in the *P* value, as based on prior research in animals and humans, you are already quite certain that reducing salt intake will lower blood pressure; you're pretty sure that the null hypothesis that "Salt intake has no effect on blood pressure" is false. Instead, you are very interested to know how *much* the blood pressure goes down. Reducing salt intake in half is a big deal, and if it only reduces blood pressure by 1 mm Hg, the tiny gain in life expectancy wouldn't be worth a lifetime of bland food and obsessive label-reading. If it reduces blood pressure by 20 mm with a confidence interval of ±5 mm, it might be worth it. So you should estimate the effect size (the difference in blood pressure between the diets) and the confidence interval on the difference.