A Guide to Process Behavior Charts in Excel

A process behavior chart (PBC) is a type of control chart that can monitor the variation in your process. PBC is used for time-series data, where observation points are taken at equal time intervals.

Instead of tracking each separate observation, they are collected in ‘blocks’ of data, i.e., the set of all observations for one time period form a block. For example, collecting daily observations may result in 12 blocks being created during June, or 30 blocks if you collect hourly observations over a day.

Process Behaviour Charts plot variations between each block. This variation is called ‘common cause’ because it is a variation that exists within your process, not because of external events like new staff or equipment.

Here is everything you should be aware of about these charts in Excel.

What is a Process Behavior Chart?

You typically collect data on an ongoing basis, and you want to know if there are any changes in how your process operates. For example, when running a call center in a high-volume season, you want to know if the number of calls being handled changes because this could indicate problems with your employees getting enough breaks or training. It is the best way to spot differences early, so you do not need to wait until a point in time that is too late.

Instead of plotting each observation point separately, process behavior charts track the variation between data blocks. For example, you might collect data each day and follow the average number of times a staff member answers the phone over a week.

There are two types of charts in process behavior:

Individuals
Moving range

Individuals vs. Moving Range Charts

An individual control chart tracks the variation between each observation in a block. It means that you can track how much variation is between these personal observations. For example, if you are looking at how much time it takes for each delivery to be processed, the measurements must be taken at regular intervals (i.e., hourly or daily). Then you have to take the average time of all deliveries made during that interval.

Moving range charts are used when dealing with sequential data instead of independent observations. It means that there is some relationship between each of the observations. For example, when tracking time taken for customers to be served, all measurements are influenced by each other.

How to Use the Charts in Excel?

To set up a process behavior chart in Excel, you need to save your data as a time series. Here is the methodology involved in this process:

If it is not already there, insert the Data Analysis command into your toolbar (formulas > analysis tools > data analysis). You can also use the keyboard shortcut Ctrl + Alt + D.
Select the Time Series option from the data analysis dialog box that appears, and then click OK. It will open a new line in your worksheet where you will set up this chart.
Add a heading for each variable you want to track (e.g., time or cost). If you are going to study any time series, whether it is months of the year, days in a week, or minutes for each customer service call, you need to separate these observations with commas.
Then enter your data into the cells under each heading. They do not need to be in order.
Now select your data and go to the Insert tab > Charts group > Scatter (X, Y) option:
From the chart dialog box that appears, choose either a Line or XY (Scatter) chart type but not both at once:
Line Chart Type: is used for when your observations are continuous, and there is a pattern to the data that forms over time.
XY (Scatter) Chart Type: is used for when your observations are discrete and there’s no pattern to the data. It just looks like a set of individual points.
Select your chart layout and choose a line or scatter option depending on which chart you are using.
Finally, select the ‘Add Chart Element’ button on your toolbar and click on the process behavior option. It will open a dialog box that allows you to create an individual or moving range chart depending on which type of data you have.

How to Interpret the Charts in Excel?

The critical thing to remember about process behavior charts is that they look at the amount of variation between your observations. It makes them very useful for evaluating whether there is any unique cause variation influencing your measurements or just common cause variation due to small changes within your process.

If you see any points on the chart outside of your control limits, there is often some unique cause variation influencing your results.

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