A histogram (or frequency distribution chart) is a bar graph that groups data by predetermined intervals to show the frequency of the data set. It provides a way to measure and analyze data collected about a process or problem, and may provide a basis for what to work on first.
Histograms are also useful for displaying information such as defects by type or source, delivery rates or times, experience or skill levels, cycle times, or end user survey responses. When sufficient process data is available, a histogram displays the central point (average) of the process, variation (standard deviation and range), and shape of distribution.
Histograms can explain graphically whether a process is in control or out of control, but they are not a substitute for statistical process control charts. They can also provide insight on the process capability to meet user specifications