# Null Hypothesis

## What Is a Null Hypothesis

A **null hypothesis** is a statement that there is no difference between two groups or that there is no association between two variables. In other words, the null hypothesis assumes that any observed differences are due to chance.

For example, imagine you are testing whether a new diet pill helps people lose weight. The null hypothesis would be that the pill has no effect on weight loss. If you give the pill to a group of people and they don't lose any weight, you can't say for sure that the pill doesn't work. It could be that the pill just wasn't strong enough, or maybe it only works for certain types of people.

To know if the pill works, you need to do a controlled experiment. You would give the pill to one group of people and not give it to another group (the control group). If the people who took the pill lost more weight than the people who didn't, then you could say that the pill was effective.

The null hypothesis is important because it is the starting point for statistical tests. Statistical tests are used to determine whether the results of a study are due to chance or if they are meaningful.

If the null hypothesis is true, then any observed differences between groups are due to chance. In order for a difference to be considered statistically significant, it must be unlikely to have occurred by chance. The significance level is usually set at 0.05, meaning there is a 5% chance that the results are due to chance.

If the null hypothesis is false, then the observed differences are likely not due to chance. In other words, there is a statistically significant difference between the groups.

The null hypothesis is usually denoted by H0, while the alternative hypothesis is denoted by H1. The alternative hypothesis is the opposite of the null hypothesis - it states that there is a difference between two groups or an association between two variables.

In order to determine whether the null hypothesis should be rejected or not, statistical tests are used. These tests calculate a p-value, which is the probability of observing the results of a study if the null hypothesis is true. The null hypothesis is usually rejected if the p-value is less than 0.05.

The null hypothesis is an important concept in statistics, and it is important to understand how to formulate a null hypothesis before performing any statistical tests.

## Why Do We Use Null Hypothesis

There are many reasons why we use null hypotheses:

First, the null hypothesis allows us to test a specific proposition.

Second, the null hypothesis allows us to set up a statistical model that can be used to make predictions.

Third, the null hypothesis allows us to compare the results of our study to other studies that have been conducted.

Fourth, and perhaps most importantly, the null hypothesis protects against Type I errors. A Type I error is when we reject the null hypothesis when it is actually true. This error can lead to false positive results, which can be very costly and cause a lot of harm.

The null hypothesis is a very important concept in statistics and scientific research. It allows us to test specific propositions and make predictions based on statistical models. Additionally, the null hypothesis protects against Type I errors, which can be very costly.

## How Do You Identify Null Hypothesis

To identify the null hypothesis, you need to understand what your research is trying to compare. For example, if you are comparing the average math scores of two groups of students, the null hypothesis would be that there is no difference between the two groups' scores.

Once you have identified the null hypothesis, you can then start to look for evidence that disproves it. This evidence can come from many sources, including experiments, surveys, and observational studies. If you find enough evidence to disprove the null hypothesis, then you can reject it in favor of a more accurate hypothesis.

## When to Reject Null Hypothesis

It is important to know when to reject the null hypothesis, as this can have far-reaching implications. The null hypothesis is a statement that there is no difference between two groups or that a certain effect does not exist. To reject the null hypothesis means that you believe there is a difference between the groups or that the effect exists.

There are several ways to test for the existence of a difference or effect. One way is to use a statistical test. These tests will tell you whether or not the null hypothesis can be rejected. If the p-value (probability value) associated with the test is less than 0.05, then you can reject the null hypothesis. This means that there is a less than 5% chance that the difference between the groups is due to chance, and therefore, you can say with 95% confidence that the difference is real.

Another way to decide whether or not to reject the null hypothesis is by looking at the effect size. The effect size is a measure of how large the difference between two groups is. If the effect size is large, then it is more likely that the difference is real and not just due to chance. For example, if Group A has an average score of 80 on a test and Group B has an average score of 60, the difference between the groups is 20 points. This would be considered a large effect size.

In general, you should only reject the null hypothesis if the evidence against it is very strong. If you are unsure, it is always best to err on the side of caution and not reject the null hypothesis. This is because rejecting the null hypothesis when it is actually true is much more serious than failing to reject the null hypothesis when it is false. Rejecting the null hypothesis when it is true is called a Type I error, and failing to reject the null hypothesis when it is false is called a Type II error.

## Why Do We Reject Null Hypothesis

We reject the null hypothesis when the evidence shows that there is a difference between the two groups. We do this because we want to be sure that the difference we see is not due to chance.

There are several reasons why it is important to reject the null hypothesis. First, if we accept the null hypothesis when there is actually a difference between the groups, we may miss an important finding. Second, if we always reject the null hypothesis, we may find false positives - differences that appear to be real but are actually due to chance.