Run Charts are fundamental graphical tools used in the Lean Six Sigma Measure Phase to display data points over time, helping teams identify trends, patterns, and variations in a process. These visual representations plot individual measurements on the vertical axis against time or sequence on the …Run Charts are fundamental graphical tools used in the Lean Six Sigma Measure Phase to display data points over time, helping teams identify trends, patterns, and variations in a process. These visual representations plot individual measurements on the vertical axis against time or sequence on the horizontal axis, creating a simple yet powerful way to monitor process performance.
The primary purpose of Run Charts is to detect non-random patterns that indicate special cause variation versus common cause variation. By examining the data points in relation to the median line, practitioners can determine whether a process is stable or experiencing shifts that require investigation.
Key elements of a Run Chart include the horizontal centerline (typically the median), data points connected in chronological order, and clear axis labels. The median is preferred over the mean because it is less sensitive to outliers and provides a more robust reference point.
Run Charts use specific rules to identify non-random patterns. A shift occurs when six or more consecutive points fall on one side of the median. A trend is identified when five or more consecutive points move consistently upward or downward. Too few or too many runs (clusters of points on one side of the median) also indicate non-random behavior.
In the Measure Phase, Run Charts help teams establish baseline performance before implementing improvements. They provide visual evidence of process behavior and support data-driven decision making. Unlike control charts, Run Charts do not include calculated control limits, making them simpler to create and interpret.
Benefits include ease of construction, minimal statistical knowledge requirements, and effectiveness in communicating process performance to stakeholders. They serve as excellent starting points before advancing to more sophisticated statistical process control methods and help teams understand whether observed changes are meaningful or simply natural process variation.
Run Charts: A Complete Guide for Six Sigma Green Belt
What is a Run Chart?
A run chart is a simple graphical tool that displays data points in time sequence order, connected by a line. It shows how a process performs over time by plotting individual measurements against a timeline. The chart includes a horizontal centerline, typically representing the median or mean of the data, which helps identify patterns and trends.
Why are Run Charts Important?
Run charts are fundamental to the Measure Phase because they:
• Provide a visual representation of process performance over time • Help distinguish between common cause and special cause variation • Enable teams to identify trends, shifts, and patterns in data • Serve as a baseline for process improvement efforts • Are simple to create and interpret, making them accessible to all team members • Help determine if a process is stable before calculating process capability
How Run Charts Work
To create and analyze a run chart:
Step 1: Collect data points in chronological order (typically 20-25 points minimum)
Step 2: Plot the data points on a graph with time on the x-axis and the measured value on the y-axis
Step 3: Connect the data points with a line
Step 4: Calculate and draw the median line (middle value when data is arranged in order)
Step 5: Analyze the chart for non-random patterns
Key Patterns to Identify
Runs: A run is a sequence of consecutive points on one side of the median. Too few or too many runs indicate non-random behavior.
Trends: Six or more consecutive points moving in the same direction (all increasing or all decreasing) suggest a trend in the process.
Shifts: Eight or more consecutive points on one side of the median indicate a process shift.
Astronomical Points: Data points that are obviously different from the rest of the data, indicating unusual occurrences.
Run Chart vs Control Chart
Run charts differ from control charts in that they do not have upper and lower control limits. Run charts are simpler and focus on detecting patterns, while control charts provide statistical control limits for more rigorous process monitoring.
Exam Tips: Answering Questions on Run Charts
• Remember the rules: Memorize that 6 points trending and 8 points on one side of the median are the standard thresholds for identifying non-random patterns
• Know the centerline: Run charts typically use the median as the centerline, not the mean. This is a common exam question
• Minimum data points: Remember that 20-25 data points are recommended for meaningful analysis
• Distinguish from control charts: If asked about the difference, emphasize that run charts lack control limits and are used for pattern detection rather than statistical process control
• Purpose in Measure Phase: Run charts help establish baseline performance and determine process stability before calculating capability metrics
• Non-random signals: Be prepared to identify which patterns indicate special cause variation versus common cause variation
• Calculation questions: You may be asked to count runs or identify trends from a given chart. Practice counting consecutive points above or below the median
• Application scenarios: Expect questions asking when to use a run chart versus other tools. Run charts are best for initial process analysis and ongoing monitoring of simple processes
• Interpretation focus: When analyzing exam scenarios, look for evidence of trends, shifts, or an unusual number of runs that would indicate the process is not in a state of statistical control