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Patterns of Variation
There are three common patterns of variation:
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Bi-Modal—Has two or more peaks. A bimodal distribution signals that
the process has a special cause of variation present. Something has
changed in the process. There are operating differences between
shifts, changes in processing methods, temperature and humidity
differences, equipment differences, raw material changes, or other
differences.
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Skewed—Looks like a normal curve pushed over to one
side. Skewed distributions also raise a red flag. But unlike
bi-modal distributions, this non-normal distribution may just be
showing the natural variation in the process if there is a natural
upper or lower limit to the data. It could also show a problem in
the process.
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