# 3: Descriptive Statistics

• • Contributed by John H. McDonald
• Associate Professor (Biological Sciences) at University of Delaware

• 3.1: Statistics of Central Tendency
A statistic of central tendency tells you where the middle of a set of measurements is. The arithmetic mean is by far the most common, but the median, geometric mean, and harmonic mean are sometimes useful.
• 3.2: Statistics of Dispersion
Summarizing data from a measurement variable requires a number that represents the "middle" of a set of numbers along with a measure of the "spread" of the numbers. You use a statistic of dispersion to give a single number that describes how compact or spread out a set of observations is. Although statistics of dispersion are usually not very interesting by themselves, they form the basis of most statistical tests used on measurement variables.
• 3.3: Standard Error of the Mean
Standard error of the mean tells you how accurate your estimate of the mean is likely to be.
• 3.4: Confidence Limits
Confidence limits tell you how accurate your estimate of the mean is likely to be.

## Contributor

• John H. McDonald (University of Delaware)