Whenever you conduct a hypothesis test, you will get a test statistic as a result. To determine if the results of the hypothesis test are statistically significant, you can compare the test statistic to a** Z critical value**.

If the absolute value of the test statistic is greater than the Z critical value, then the results of the test are statistically significant.

Fortunately, Excel makes it easy to find Z critical values using the following function:

**NORM.S.INV(probability)**

where:

**probability:**The significance level to use.

This function returns a Z critical value, based on the significance level you chose.

This tutorial provides three examples of how to use this function to find Z critical values.

**Example 1: Two-Tailed Test**

**Find the Z critical value for a two-tailed test, using α = 0.10.**

For a two-tailed test, there will be two critical values:

**NORM.S.INV(α/2)****NORM.S.INV(1-α/2)**

We can use the following functions in Excel to calculate these critical values:

Thus, the two critical values for this test are **-1.645** and **1.645**. This means if the test statistic is less than -1.645 or greater than 1.645, then the results of the hypothesis test are statistically significant.

**Example 2: Right-Tailed Test**

**Find the Z critical value for a right-tailed test, using α = 0.05.**

For a right-tailed test, there will be one critical value: **NORM.S.INV(1-α)**

We can use the following function in Excel to calculate this critical value:

Thus, the critical value for this test is **1.645**. This means if the test statistic is greater than 1.645, then the results of the hypothesis test are statistically significant.

**Example 3: Left-Tailed Test**

**Find the Z critical value for a left-tailed test, using α = 0.01.**

For a left-tailed test, there will be one critical value: **NORM.S.INV(α)**

We can use the following function in Excel to calculate this critical value:

Thus, the critical value for this test is **-2.326**. This means if the test statistic is less than -2.326, then the results of the hypothesis test are statistically significant.