- Definition: A Run Chart is a statistical tool to assess, monitor, and maintain process stability. The main purpose is to monitor a particular activity or continuous process in order to discover any deviation or variation of this activity or process so we can prevent defects, avoid waste of time, reduce costs, etc.
Example 1) Draw a run chart and interpret it for the costs of operations over 20 months in the launching area.
Step 1: Calculate the average cost $ \bar X $
$ \bar X = ( 128 + 48 + 211 + 45 + ... + 87 + 48 + 75) / 20 $
$ \bar X = 75.3 $
Step 2: Draw a simple line graph
Step 3: Interpretation
1) Look for patterns such as cycles, trends or changes.
2) Observe if the average value line represents the desired behavior level.
3) Not all the changes or variations are important.
Following the change of an activity or process statistically where the activities are repeated, which is also one of the principles of this tool, we can find two types of variation:
- Common or random: are variations inherent to the process and usually comes from various sources of minor variations. Eliminating the Common Causes is more difficult because it requires knowledge and analysis of the entire change process: procedures, people, patterns, etc ..
- Special or exclusive events: are variations that occasionally arise in the process and the elimination of this variation is generally related to execution of the activities of that process. Once identified the Special Cause Variation, it must to be eliminated and prevent recurrence of the same cause with a preventive action is required.