Measures of Variation

A population is all the data that exist for a process. A sample is a small group of data randomly taken from a population that is representative of the whole population.

Three statistical measures of variation are:

Mean

• The arithmetic average of the sample.
• This measures the location of the process output.

Range

• The highest data point minus the lowest data point.
• This is one of two measures of the variation in the process.

Standard Deviation

• A statistic that measures how data cluster around the mean.
• This is another measure of variation.
• The smaller the standard deviation, the less variation there is in a process. The larger the standard deviation, the more variation there is in a process.