Descriptive Statistics

Standard Deviation

Standard deviation is simply the square root of variance. As such, standard deviation is a reflection of how (in)consistent the values are in the data. If the values are all practically the same, the standard deviation will be low. If the values are "all over the place," the standard deviation will be high.

In statistics, there is another use of the phrase "standard deviation" that refers to the distribution of a statistic (i.e., not the distribution of a measure as described above but instead the distribution of an inferential statistic such as a population mean). For the purposes of this class, this terminology will be avoided because it is unnecessarily confusing for the task at hand. In this class -- as in real-world marketing research -- whenever you hear the words "standard deviation," they will be referring to the simple and straightforward descriptive statistic that is described above.

"Standard deviation" should not be confused with "standard error" because they refer to fundamentally different ideas. It's too bad those names are so similar, but tradition rarely favors clarity.