Normal distribution

how can you tell if something is normally distributed?

You can use the empirical rule (68% of data within 1 sd, 95% within 2 SD, 99.7% within 3 SD) and see if the data tends to conform to that.

You can also use a normal probability plot by graphing it on your calculator.

The normal distribution shows a graph that is bell-shaped, meaning most of the data is in the middle, with less and less as you approach either end of the graph. On the exam, be aware of the normal condition. For proportions, np>10 and n(1-p)>10. For means, population must be normal or n>30 to use the central limit theorem.

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