Normal distributions are a family of distributions that have the shape shown below.

Normal distributions are symmetric with scores more concentrated in the middle than in the tails. They are defined by two parameters: the mean (μ) and the standard deviation (σ). Many kinds of behavioral data are approximated well by the normal distribution. Many statistical tests assume a normal distribution. Most of these tests work well even if the distribution is only approximately normal and in many cases as long as it does not deviate greatly from normality.

The formula for the height (y) of a normal distribution for a given value of x is:

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