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Designed to help those that are preparing to take the PMP or CAPM Certification Exam, each post within this series presents a comparison of common concepts that appear on the PMP and CAPM exams.
Control Chart vs Run Chart
There are a number of charts used to evaluate and analyze quality results within a project. Two charts that are similar and often confused are a control chart and a run chart.
Control charts are used to determine whether or not a process is stable or has predictable performance.
Typically, control charts identify upper and lower control limits to determine the acceptable range of test results.
Control charts commonly have three types of lines:
- Upper and lower specification limits
- Upper and lower control limits
- Planned or goal value
Control charts illustrate how a process behaves over time and defines the acceptable range of results. When a process is outside the acceptable limits, the process is adjusted.
Control charts can be used for both project and product life cycle processes. For example, for project processes a control chart can be used to determine whether cost variances or schedule variances are outside of acceptable limits.
A run chart is a line graph that shows data points over time. Run charts are helpful in identifying trends and predicting future performance.
Run charts are similar to control charts, plotting data results over time, however there are no defined control limits.
A control chart may be used for a pharmaceutical company that is testing a new pain medication. The drug must stay effective in the system for a minimum of three hours but last no more than five hours, to prevent accidental overdose.
The mean time or goal efficacy duration would be four hours, with three hours the lower control limit and five hours the upper control limit.
A run chart may be used to plot the temperature within the manufacturing plan every day for a month to determine a trend.
While both a run chart and a control chart plot data points over time or batches, the control chart is enhanced with defined control limits and a target or goal delineation.
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