XLSTAT: One Sample Variance Test in Excel

 

Dataset for Example

A nail factory has acquired a nail production machine. An engineer wants to test if the machine produces nails with nail head diameter variability lower than a standard of σ = 0.065 (Standard Deviation).

Data are nail diameters measured on 50 nails produced by the machine. They can be downloaded by clicking on the link given at the beginning of this tutorial.

The goal is to check if an observed variance is different from a theoretical one. The test we will manipulate for this purpose can be very useful in Statistical Process Control.

Setting Up

• Open XLSTAT.
• Click on the Parametric tests menu and select the One-sample Variance test feature:

• In the General tab, select the data under the Data field.

• In the Options tab, enter the theoretical variance in the appropriate field: σ² = 0.065² = 0.004225.

• Click on the OK button to launch the computations.
• The results are displayed on a new Excel sheet.

Interpreting the Results

The estimated variance is 0.0024, below the standard of 0.004225. Its 95% confidence interval ]0.0016, 0.0037[ excludes the standard. With a p-value of 0.0103 (< 0.05), we conclude that the machine's variability is significantly lower than the standard, with a 1.03% risk of error.

The mean of nailhead diameter can be compared to a standard using the One Sample T Test .