Statistics How To

How to Create a Normal Probability Plot in Minitab

Normal probability plots > Normal probability plot in Minitab

 

Normal probability plot in Minitab

A normal probability plot.

A normal probability plot is one way you can tell if data fits a normal distribution (a bell curve). With this type of graph, z-scores are plotted against your data set. A straight line in a normal probability plot indicates your data does fit a normal probability distribution. A skewed line means that your data is not normal. (“Not normal” in this sense means that it doesn’t fit a bell curve). Watch the video below to learn how to create a normal probability plot in Minitab or read the steps below.

How to create a normal probability plot in Minitab

Step 1: Type your data into columns in a Minitab worksheet. Give your variables meaningful names in the first (blank) row (this makes it easier to build the plot when you select a variable name in Step 4).

Step 2: Click “Graph” on the toolbar and then click “Probability plot.”

Step 3: Click the “Single” probability plot image. This is the option you’re likely to use 99% of the time in elementary statistics.

Step 4: Choose a variable name and then click “Select” to move the variable name to the Graph Variables box. If you didn’t name your variables in Step 1, the variable names will be listed as column identifiers (C1, C2 etc.).

Step 5: Click “OK.” Minitab will create a normal probability graph in a new window.

Tip: Make a histogram in minitab to see how well your data fits a normal distribution. Often a normal probability plot will appear to be fairly straight, but it might not be a great match to a bell curve. Checking the histogram first will allow you to see if your data fits a bell curve before you make assumptions about your data using the normal probability plot.

If you prefer an online interactive environment to learn R and statistics, this free R Tutorial by Datacamp is a great way to get started. If you're are somewhat comfortable with R and are interested in going deeper into Statistics, try this Statistics with R track.

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How to Create a Normal Probability Plot in Minitab was last modified: October 12th, 2017 by Andale