### Chapter 1. Descriptive Statistics: Frequency Distributions

### Shape of a Distribution

A distribution is **symmetrical **when the left and right side of the distribution are each other's mirror image.

A special type of symmetrical distribution is the *uniform* distribution. In a **uniform **distribution, all scores occur with the exact same frequency. The resulting graph is shaped like a rectangle.

Most distributions, however, are not symmetrical. More often than not, a distribution will exhibit some degree of *skewness*. A distribution is **skewed **when its scores are unevenly distributed among the left and right side of the scale. Skewed distributions are identified by the tail-end of the distribution.

For a **positively skewed** or **right-skewed** distribution, the tail of the distribution points to the right (positive) side of the scale. Positively skewed distributions are characterized by a relatively large amount of low scores and few high scores. A common example of a positively skewed distribution is the distribution of income.

For a **negatively skewed** or **left-skewed** distribution, the tail of the distribution points to the left (negative) side of the scale. Negatively skewed distributions are characterized by relatively few low scores and a large number of high scores. Examples of a negatively skewed distribution are retirement age and human lifespan.

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