# Variance ratio test (F-test)

Command: | Statistics Variance ratio test (F-test) |

## Description

The F-test is used to compare the variances of two samples.

## Required input

In the dialog box first identify the variables for sample 1 and sample 2. You can use the button to select variables and filters in the variables list.

### Options

Logarithmic transformation: select this option if the data are positively skewed.

## Results

The program displays summary statistics and the variances of the two samples. Next the results of the variance ratio test and the F-statistic is given, which is the ratio of the larger variance over the smaller, with its associated (two-sided) P-value. If the P-value is less than the conventional 0.05, the null hypothesis is rejected and the conclusion is that the two variances differ significantly.

### Logarithmic transformation

If you selected the Logarithmic transformation option, the program will give the back-transformed summary statistics. The variance of the logs cannot be back-transformed meaningfully and therefore the variances and the variance ratio are given on the log-transformed scale.

## Literature

- Bland M (2000) An introduction to medical statistics, 3
^{rd}ed. Oxford: Oxford University Press.