Histogram
 

Description:

One of the Total Quality Management Tools is  the Histogram.

One uses this graph to show frequency distributions. It looks very much like a bar chart.

When to Use:

This chart graphs data distrubutions. If you have numerical, variablle, continuous data you can use the this chart. The chart organizes and sorts the data. It shows the data in a pictorial format.
 

Construction :
 

• Collect at least 50 data points from a process.
 

• Use the worksheet below to set up the chart. It helps you determine the number of bars, the width of the bar, and the labels for the bar edges.
 

• After calculating width in step 2 of the worksheet, use your judgment and adjust it to a convenient round number. For example, you might decide to round 0.9 to an even 1.0. The value for W may not have more decimal places than any number in your data set.
 

• Draw x- and y-axes on graph paper. Mark and label the y-axis for counting the data values. Mark and label the x-axis with the L values from the worksheet. The spaces between these numbers will create the bars. Do not allow for spaces between bars.
 

• For each data point, locate it where it fits within the Ls. Mark off one count above the appropriate bar with an X or by shading that portion of the bar.
 

Example

• Consider this simple example. Below shows the exam results collected from a training class of 50 individuals:

Below is the chart. The center of the data shows about 69. The average is probably near 69.   Construct these bar charts to provide a useful picture of your data.
 

To see many examples of histogram and learn more details, see this page