A histogram, sometimes called a frequency plot or frequency distribution, graphically shows the distribution of a data set–including display of central location (mean, median, and mode), shape, and spread of data. It is often used in combination with a run or control chart to further study process performance. It can also be used when the sequencing of data has not been preserved. The X axis is built of several consecutive groupings, called cells, using continuous data like time, weight, size, or temperature. The Y axis is typically a count or percent within each cell.
The reader is referred to the Institute for Healthcare Improvement’s website for complete instructions and another example.
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Murray, Sandra K. & O. Bryan Murray. Practical Tools for Healthcare Quality:Total Quality Transformation. PQ Systems, 1997, 107-125.