When is a variable normally distributed? One way to tell is with the following (from page 104-105 of ES7):

**Empirical Rule**- If a variable is normally distributed, then:

within one standard deviation of the mean there will be approximately 68% of the data;

within two standard deviations of the mean there will be approximately 95% of the data; and

within threestandard deviations of the mean there will be approximately 99.7% of the data. - Copy the values of the column of interest into the clipboard: Highlight the column, and
choose
.`Edit>Copy` - Choose
and select NORMRULE.jmp. (trouble opening this file in JMP?).`File>Open` - Paste the values on the clipboard into the first column: Change the column name from
`SCORE`to the original column name from the source dataset. Highlight the first column. Choose.`Edit>Paste` - The calculations automatically occur and the results appear in the data table.
- Choose
.`Analyze>Distribution of Y` - Select the columns
(using Shift-click). The**~68%**,**~95%**,**~99.7%**report displays the proportion of rows with values of 1 and you can compare these with the expected percentage.`Distribution of Y` - Navigation
JMP templates JMP ropes Links for JMP users Al's Home Page eMail: AlBest@VCU.edu *modified: 16Sep 96*

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normal distribution

On pgs. 104-107 in ES7 an empirical rule is given for checking normality. To check a set of values with this rule, use the NORMRULE template. The template as one data column, SCORE, and three calculated columns.

`NORMRULE
`

The formula for the column ~95% is as follows (and the others are similar).

The formulas calculate 0/1 values according to whether the original variable is within 1, 2, or 3 standard deviations.

To calculate the observed proportions, calculate the mean of these calculated columns.

A.M. Best and R.K. Elswick (1996) *JMP IN® Companion for Robert Johnson's ELEMENTARY STATISTICS, Seventh Edition.* Duxbury
Press. (pp 132-133). ISBN 0-534-24317-7

© Copyright 1996 by Data-Ink. All Rights Reserved.

Published by Duxbury Press, an
imprint of Brooks/Cole Publishing Company, a
division of International Thomson Publishing
Inc.