# T-Test

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## Definition of 'T-Test'

A t-test is a statistical test used to compare the means of two groups. It is used to determine whether there is a statistically significant difference between the means of the two groups.

The t-test is a parametric test, which means that it makes certain assumptions about the data. These assumptions include:

* The data is normally distributed.
* The variances of the two groups are equal.

If these assumptions are not met, then the results of the t-test may not be valid.

The t-test is a powerful tool for comparing the means of two groups. However, it is important to understand the assumptions of the test and to make sure that the data meets these assumptions before using the test.

Here is a step-by-step guide on how to perform a t-test:

1. State the null and alternative hypotheses.
2. Choose a significance level.
3. Calculate the t-statistic.
4. Determine the critical value.
5. Make a decision about the null hypothesis.

Let's take a look at an example of how to perform a t-test.

Suppose we want to compare the average weight of two groups of students. The first group is made up of students who are taking a statistics course, and the second group is made up of students who are not taking a statistics course.

We would first need to state the null and alternative hypotheses. The null hypothesis would be that there is no difference in the average weight of the two groups. The alternative hypothesis would be that there is a difference in the average weight of the two groups.

We would then need to choose a significance level. A significance level of 0.05 is commonly used.

We would then need to calculate the t-statistic. The t-statistic is calculated by dividing the difference in the means of the two groups by the standard error of the difference in the means.

The standard error of the difference in the means is calculated by taking the square root of the sum of the variances of the two groups divided by the sample size of each group.

Once we have calculated the t-statistic, we need to determine the critical value. The critical value is the value of the t-statistic that would be needed to reject the null hypothesis.

The critical value is determined by the significance level and the degrees of freedom. The degrees of freedom are equal to the number of observations in each group minus 1.

If the t-statistic is greater than the critical value, then we would reject the null hypothesis. This would mean that there is a statistically significant difference between the means of the two groups.

If the t-statistic is less than the critical value, then we would fail to reject the null hypothesis. This would mean that there is no statistically significant difference between the means of the two groups.

Here is an example of how to interpret the results of a t-test.

Suppose we performed a t-test and found that the t-statistic was 2.0 and the critical value was 1.96. In this case, we would reject the null hypothesis because the t-statistic is greater than the critical value. This would mean that there is a statistically significant difference between the means of the two groups.

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