Run Charts are simple line graphs of data plotted over time. They are used to better-understand the performance of a process, as they help people distinguish between random variation and special causes, or to track information and predict trends or patterns.
A run chart can also reveal whether a process is stable by looking for a consistent central tendency, variation and randomness of pattern.
One of the most common CI tools, a run chart is easy to interpret and does not require tedious calculations or special software to produce.
How to create a run chart:
- Identify the question that the run chart will answer and obtain data that will answer the question over a specified period of time. For example, if you were looking at how long it takes to complete a task, you will make note of the time taken (in minutes) to complete it over a specified period of time.
- Gather data, generally collect at least 10 data points to detect meaningful patterns.
- Create a graph with vertical line (y axis) and a horizontal line (x axis).
- On the vertical line (y axis), draw the scale related to the variable you are measuring. In our example, this would include the complete range of observations measuring time-to-completion
- On the horizontal line (x axis), draw the time or sequence scale.
- Plot the data, calculate the median and include into the graph.
- Interpret the chart. Four simple rules can be used to distinguish between random and non-random variations:
- Shift – 6 consecutive points above or below the median
- Trend – 5+ consecutive points going up or down
- Too many/too few runs – too few or too many crossings of the median line
- Astronomical data point – a data point that is clearly different from all others (often a judgement call)