Run charts can be used to monitor the changes associated with a particular characteristic over time. Run chart provide a more sophisticated method of deciding if your process is stable. Run charts are quick and easy tool that help you to decide if your process is statistically stable.
Plotting data over time on a graph is a simple and effective way to determine whether the changes you are making are leading to improvement.
The run charts that help us talk about the changes that we made or things that were going on the environment, and give us ideas about what's happening as we're looking at the behavior of the process.
A run chart includes several elements. On the left side of the graph is Y-axis, this is what our data is about. The bottom is the x-axis, and this shows the time series in which you're tracking your data. This can be days, weeks, months, sometimes even years. Here in this above graph X-axis is number of samples.
In the middle we have a line that's the median. In addition, we want to be really, really clear when we're thinking about our display to label everything. Labeling the y and the x-axis, putting in a very, very clear title.
Minitab plots the value of each data point in the order that they were observed. You can examine the run chart to see if there are any obvious patterns, but Minitab includes two tests for randomness that indicate whether there are any statistically significant patterns or evidence of non-randomness.
To draw a run chart, you can follow the below process.
1. Plot time along the X axis. Choose the appropriate time increment based on your improvement project — minutes, hours, days, weeks, months, etc. Note that individual samples could also be the unit plotted on the X axis.
2. Plot the key measure you’re tracking along the Y axis. Note that a run chart becomes more powerful as you add more data points because there will be more opportunities to identify patterns. If you’re looking for signs of improvement, usually you need at least 10 data points.
3. Label both the X and Y axes, and give the graph a useful title.
4. Calculate and place a median of the data on the run chart. The median is the number in the middle of the data set when the data are ordered from the highest to the lowest. A baseline or Median is a horizontal reference line that runs all the way across the chart. It helps you understand your performance BEFORE you started your tests of change, to give you a basis for comparison. The baseline should be the median. Note that you need at least five data points to create the baseline median.