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A skewed frequency distribution is a distribution in which the data is not spread evenly — rather, the data is clustered at one end. In this case, the mean and the median are not equal, causing the data set to be skewed. A skewed distribution is neither symmetric nor normal. In general, there are two types of skewed frequency distributions.
| Skewed Distribution | Description |
|---|---|
| Skewed Left / Negatively Skewed | The distribution has a long left tail and the median is greater than the mean. |
| Skewed Right / Positively Skewed | The distribution has a long right tail and the median is less than the mean. |
The difference between normal and skewed distributions can be visualized in the following applet.
The measures of center and spread that best describe a skewed distribution are the median and the five-number summary, respectively. The median is preferred because it is less affected by outliers, while the mean will fall in the direction of the tail of the distribution.