The t-test is a statistical test used to compare whether the means of two groups are significantly different from each other. It is especially useful in medical research when it is desired to assess, for example, whether a new treatment produces an effect different from the standard treatment or placebo.

This test is based on Student's t-distribution, which is applied when, under the null hypothesis (i.e., assuming that there is no real difference between the groups), the test statistic follows that distribution.

The t-test is mainly used in situations where, if the real variability of the population (variance) were known, the statistic would follow a normal distribution. However, in practice, this variance is usually unknown, and so it is estimated from the available data. Under certain conditions, this estimation allows the statistic to follow a t-distribution, which makes it possible to perform the test rigorously.

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Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on September 10, 2019.