# 4 Z-test vs t-test

Now you will explore two fundamental statistical tests for comparing means: the z-test and the t-test. Understanding these tests is crucial for making accurate comparisons and drawing valid conclusions in various business scenarios.

The key factor in choosing between a z-test and a t-test is whether you know the population standard deviation:

- Z-test: Use when the population standard deviation is known.
- T-test: Use when the population standard deviation is unknown.

OpenLearn - Data analysis: hypothesis testing
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