How do I use the empirical rule?

1 Answer
Mar 5, 2015

It can give you quick answers without looking up in tables.

Ususally, you standardise the normal distribution, and then look up its z-value in a table.
If you memorise just a few numbers, you can work quicker.
The numbers are #34,13.5 and 2.5# meaning:
#34%# of your values will be within one standard deviation above the mean, and #34%# will be within one STD below the mean.
#13.5%# will be between one and two STD above (and #13.5%# will be between one and two STD below)
The remaining two times #2.5%# will be outside that.

Below is a graph (from Wikipedia) that summarizes:

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