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The Three Coolest Things You Didn't Know about Histograms in Minitab

Not too long ago, I observed that one number is rarely adequate to describe data. Means and medians can disagree, and it’s important to know whether different groups of data have similar spreads. A great tool for displaying a more complete representation of the data is the histogram. Histograms are an easy way to summarize a lot of statistics. If you’re not convinced, take a minute to explore some. For example, Katherine Roswell can give you an example of how to use a histogram to identify the best opportunity for improvement in hospital patient readmissions. Histograms are great.

And the truth is, that creating histograms in Minitab is pretty great, too. They’re fast and they’re easy. But if you can already get through an easy example of a histogram in Minitab and are ready for some more, here are the three coolest things you didn’t know about histograms in Minitab.

You need only two numbers to define your bins.

Once you enter your data, Minitab follows an algorithm that makes a pretty good standard histogram. That doesn’t mean that you wouldn’t want to explore a little bit and see if small changes affect how the histogram looks.

Histogram of length of stay

To easily re-define the bins:

  1. Double-click one of the bars.
  2. Select Binning.
  3. Select Midpoint/Cutpoint positions.
  4. In Midpoint/Cutpoint positions enter 2 consecutive midpoints or enter values that define a single bin for your data. Click OK.

"Enter two values?" You might say. "But I want to have 20 bins on my graph!" Minitab makes this easy. When you enter two values, Minitab expands the range of the bins to encompass the rest of your data. So if all you enter is two numbers:

5 and 6 are the midpoints of two bins

then Minitab does the rest of the work for you.

Histogram of length of stay with 1 day bins

You can make histograms that are easy to compare.

Sure, you're good at Minitab, so you know how easy histograms make it to analyze the features of a single sample of data. But did you know they're great for comparing samples too?

Try this out:

  1. Choose Graph > Histogram.
  2. Choose Simple. Click OK.
  3. In Graph variables, enter 2 columns of data.
  4. Click Multiple Graphs.
  5. Select In separate panels of the same graph.
  6. Under Same Scales for Graphs, check Same Y and Same X, including same bins. Click OK twice.
  7. Right-click the graph and choose Panel.
  8. Under Rows and Columns, select Custom.
  9. For Rows, enter 2. For Columns, enter 1. Click OK.

Compare lengths of stay for different types of surgeries

Now you have histograms with the same horizontal and vertical scales that make it easy to see how the samples differ.

You can create histograms from tallied data.

So you're great at histograms in Minitab. You can switch bins around and panel to your heart's content. But some day, someone is going to give you data that they've tallied instead of the nice single numeric column you're used to working with. Imagine, if you will, that it lands on your desk looking something like this:

Tallied data on the back of a messy expired coupon.

A lesser person might be intimidated as well as disgusted. That data has over 300 numbers in it.  But not you. You're so good at Minitab that you know you don't have to type over 300 numbers. You can use that data just the way it is. First, enter the data into Minitab:

Length of Stay

Frequency

5

20

6

20

7

50

8

20

9

10

10

110

11

30

12

20

13

20

14

20

15

0

16

0

17

10

18

0

19

0

20

10

21

0

22

10

23

0

24

20

Then, follow these steps:

  1. Choose Graph > Histogram
  2. Choose Simple. Click OK.
  3. In Graph variables, enter Length of Stay.
  4. Click Data Options.
  5. Click Frequency.
  6. In Frequency variable, enter Frequency.
  7. Click OK twice.

You get this histogram:

Length of stay histogram from tallied data

And remember, if you want to change the bins around, you only have to use two numbers and Minitab takes care of the rest!

Now you're even more of an expert!

Whether you want to quickly explore different bins, to make comparisons between histograms, or to make a histogram from a tally, Minitab makes it fast and easy. Histograms are full of the information that you need to make good decisions about how to improve your processes. Now you know how to get even more out of histograms in Minitab.

Bonus Histogram Tip

Ready for another Minitab tip already? Check out how to make a histogram in Minitab when you have to use categories for the bins.

The data for all but the last histogram come from this study:
Stefan K. Burgdorf and Jacob Rosenberg, “Short Hospital Stay after Laparoscopic Colorectal Surgery without Fast Track,” Minimally Invasive Surgery, vol. 2012, Article ID 260273, 6 pages, 2012. doi:10.1155/2012/260273

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