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:Â 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.