# Glossary “F” Definition of Terms in DataMyte

## F Distribution

The distribution of F, the ratios of variances for pairs of samples. Used to determine whether the populations from which two samples were taken have the same standard deviation. The F distribution is usually expressed as a table of the upper limit below which F can be expected to lie with some confidence level for samples of a specified number of degrees of freedom.

## F Test

A test of whether two samples are drawn from populations with the same standard deviation, with some specified confidence level. The test is performed by determining whether F, as defined above, falls below the upper limit given by the F distribution table.

## Failure Rate

The average number of failures per unit time. Used for assessing reliability of a product in service.

## False x Causes

For x control charts: changes in the x control chart which are not due to changes in the process mean, but to changes in the corresponding R chart.

## Fault Tree Analysis

A technique for evaluating the possible causes which might lead to the failure of a product. For each possible failure, the possible causes of the failure are determined; then the situations leading to those causes are determined; and so forth, until all paths leading to possible failures have been traced. The result is a flow chart for the failure process. Plans to deal with each path can then be made.

## Feedback

Using the results of a process to control it. The feedback principle has wide application. An example would be using control charts to keep production personnel informed of the results of a process. This allows them to make suitable adjustments to the process. Some form of feedback on the results of a process is essential in order to keep the process under control.

## Figure of Merit

Generic term for any of several measures of product reliability, such as MTBF, mean life, etc.

## Fixed-Station Data Acquisition Equipment

Data collection equipment used at a fixed location: for example, permanently attached to a particular manufacturing process, or residing in a test lab.

## Flow Chart (for programs, decision-making, process development)

A pictorial representation of a process indicating the main steps, branches, and eventual outcomes of the process. Frequency Distribution — For a sample drawn from a statistical population, the number of times each outcome was observed.