- Graphical description in which we use graphs to summarize data.
- Tabular description in which we use tables to summarize data.
- Parametric description in which we estimate the values of certain parameters which we assume to complete the description of the set of data.

We have two objectives for our summary:

- We want to choose a statistic that shows how different
*units*seem similar. Statistical textbooks call the solution to this objective, a*measure of central tendency.* - We want to choose another statistic that shows how they differ. This kind of statistic is often called a
*measure of statistical variability*.

The most common measures of variability for quantitative data are the variance; its square root, the standard deviation; the statistical range; interquartile range; and the absolute deviation.

See also