The Psychology of Quality and More

A Toolbook for Quality Improvement and Problem Solving (contents)

Histogram: Practical variations

The Quality Toolbook > Histogram > Practical variations

When to use it | How to understand it | Example | How to do it | Practical variations

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Practical variations

A number of different ways of using and displaying Histograms are shown in the Table below.

Table 1. Histogram variations

Draw lines across the Histogram to ease estimation of the height of individual bars. Superimpose the expected distribution on top of the Histogram to show how close it is.
Compare the Histogram with a previous Histogram by showing the previous Histogram in outline only.
A Dot Plot shows bars as at series of dots, where each dot represents a fixed group of one or more measurements. It is useful where there are only a few measurements made, and can be used like a Check Sheet, to plot the distribution 'on the job'.
A Frequency Polygon draw a continuous line between the midpoints of where the bars would be, to emphasize the distribution.
Show the actual size of each measurement within each bar by building the bars from the measurement values. This enables the distribution within each bar to be seen. Space can be saved by putting only the fractional difference in the bar, with the full number below. This is called a Stem and Leaf Plot.

 

• Determine the number of bars by using the Sturgess rule, which calculates the number of bars as: 1 + 3.3 log10 (number of measurements).
   

• A Chumbo Chart is a reusable physical device used for manual recording and Histogram display. Bars are represented by transparent tubes and colored beads are dropped into the appropriate tube to count events.
   

• The frequency table used to organize Histogram data can be expanded to include a Check Sheet to record the events as they happen.
   

• Any Histogram can be drawn horizontally, instead of vertically. This can make labeling easier.