The purpose of this article is to explain what “control charts” are, in non-technical terms, and how they can be used within the accounting profession to analyze, control and improve accounting processes. Statistical techniques have been employed in the manufacturing environment to improve quality and maintain control. The repetitive nature of several accounting processes and procedures lend themselves very well to this type of statistical analysis.

What are Control Charts?

Control charts are graphic representations of a collection of data points from a particular process over a period of time. They contain a centerline representing the process average or expected performance, as well as, upper and lower control limits that set bounds for an acceptable area of deviation from the centerline.

How are Control Charts Used?

After a sufficient amount of data points have been plotted, it can be determined if a process is “in control” as shown in Figure 1 or “out of control” as shown in Figures 2 and 3.¹

 Figure 1

Figure 2

Figure 3

Data points falling outside the upper and lower control limits, as in Figure 2, would be investigated to determine the root cause for the deviation. As these causes are understood, corrective actions can be taken to prevent future “out of control” data points. While the data points in Figure 3 are all within the tolerance levels, the long running periods above or below the centerline indicate a change or shift in the process has occurred. The point at which the shift occurred should be investigated, so corrective action can be taken to bring the process back into control. 

Applications in Accounting

The potential applications of control charts within accounting are numerous. Here are a couple of examples.You could measure efficiency, such as days it takes to process an invoice from a shipping document or days it takes to complete a monthly close. You could use control charts to help detect errors in data, such as charting your weekly payroll. A week where the payroll is significantly higher than prior weeks would be investigated to make sure there is a valid explanation. See the table below for these and other potential applications of control charts in accounting.

As is the case with any statistical data, you must be careful to clearly define the process you want to measure and chose the appropriate type of data chart that will properly measure the process.  Selecting improper data can lead to “meaningless or misleading” results. In conclusion, proper use of control charts can help you improve performance and efficiency, which in turn can reduce cost, increase profits and improve both internal and external customer satisfaction. 

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¹ Charts have been adapted from Figure 1 of the subject article.

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