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# Excel statistical functions

###### Quick reference card

The area under the curve up to z shows the probability of getting z. These values are also available in statistics tables.

Now take a look at the Normal Distribution, which is a smooth symmetrical bell-shaped curve. If you measured the height of a sample of plants grown under the same conditions, the distribution of the heights would approximate the Normal curve.

There are two functions in Excel for the Normal Distribution: NORMDIST and NORMSDIST. If you misspell the function name (a very common error), you'll either get no answer or get the wrong one.

In the practice session you'll use the NORMSDIST function, which calculates probabilities associated with the Standard Normal Distribution. The Standard Normal Distribution curve is centered at 0 (the mean). Probability is spread out in a way consistent with the Standard Normal Distribution's standard deviation of 1. This means that about 95 percent of the distribution lies between -2 and 2. As shown in the illustration, the area under the curve up to a particular point indicates the cumulative probability of getting that value; the total area under the curve is 1.

The formula would be written =NORMSDIST(z), where you want to know how much probability lies to the left of z on the curve. You can use this function instead of a table of Standard Normal Distribution probabilities, but you have to spell the function name correctly to get the right answer.

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