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.

See also

• Independent samples t-test

Recommended book

An Introduction to Medical Statistics
Martin Bland

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This textbook is intended for medical researchers and includes the design of clinical trials and epidemiological studies, data collection, summarizing and presenting data, probability, standard error, confidence intervals and significance tests, techniques of data analysis including multifactorial methods and the choice of statistical method, problems of medical measurement and diagnosis, vital statistics, and calculation of sample size.