When data is arranged in order from lowest to highest, a pattern may emerge where the majority of the data may form a cluster around the middle. Graphing this information would produce a bell-shaped curve known as the normal distribution curve. 3 values are important when dealing with the normal curve – 68%, 95% and 99.7%. Wide, flatter curves suggest greater spread/std. deviation, whereas narrow, steeper curves suggest smaller spread between values/std. deviations. Standard scores/z-scores are the number of std. deviations a values lies above or below the mean.

#### Introduction to the normal distribution

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#### Calculation of probabilities for a normal distribution

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