Counts are simple. But obtaining the count is only half the job. In addition, you also must know the area of opportunity for that count. In fact, the area of opportunity defines the count.
And just what is the area of opportunity for a count? It depends on what is being counted, how it is being counted and what possible restrictions there might be upon the count.
Let's begin with the problem of tracking complaints. How do you count them? Do you count the number of complaints received each month? Or do you count the number of customers who complained? You will need careful instruction before you can begin to collect useful count data.
A certain pediatrics unit reported the number of concerns on a monthly basis. The values for one period of 21 months were, respectively, 20, 22, 9, 12, 13, 20, 8, 23, 16, 11, 14, 9, 11, 3, 5, 7, 3, 2, 1, 7 and 6. But even though you know the counts, you don't know the whole story because you don't know the context for the counts. Before anyone can make sense of these counts, certain questions must be answered.
For instance, how is "concern" defined? Are these customer complaints or internally generated counts? Where is the border between a concern and a nonconcern?
Why does the number of concerns drop? And what about the rumor that the hospital administrator is using these numbers to challenge the orthopedics unit to improve?
If you don't know the area of opportunity for a count, you don't know how to interpret that count.
If the area of opportunity changes over time, then the counts will not be comparable. To obtain comparable values when the area of opportunity changes, you must divide each count by its area of opportunity.
Let's assume that concerns is just an antiseptic term for complaints. You could characterize the area of opportunity for these complaints in several ways: by the number of office visits, procedures performed or hours worked by primary caregivers. The area of opportunity will determine the ways you can use the counts to understand your process. And what constitutes a complaint? Does a complaint about a chilly reception room count?
Don't despair. You can collect useful count data. The essence of the count data problem is twofold: What should you include in your count, and what area of opportunity would you use to adjust the counts to make them comparable?
Begin with a written description of what to include in your count. What is the threshold for inclusion? Give examples; the more specific the better.
Next, what is an appropriate area of opportunity for your count? You must choose an area that can be measured or counted, and that bears some clear relationship to the count. The test here is rationality. Find some logical connection between the size of the area of opportunity and the size of the count. Any one count may have several possible ways to characterize the area of opportunity, and for this reason alone, you must make an initial choice.
Say you track sales generated through your Web site. The number of Web site orders divided by the number of Web site visits would be a proportion based upon counts. But you might also want to know the proportion of sales that came from these Web site orders. This would require a ratio of measurements.
There is no simple formula for obtaining good count data. It's basically a mixture of planning and common sense, with some thought given to adjusting for variable areas of opportunity.
Of course, there is always the problem of counting events that include different degrees of severity. Many times this problem is addressed by creating categories for the different degrees and then awarding different numbers of "demerits" for each category. While it may be helpful to create such categories, you should resist the temptation of adding up the demerits.
An example of the absurdities that can result if you do comes from the University of Texas, where, in the 1960s, the campus police could issue tickets to students. The tickets came in three flavors: minor, major and flagrant. Minor violations included such things as jaywalking and littering. Four minor violations would get you expelled. Major violations included parking in a faculty space or hitting a pedestrian with your car. Two major violations would get you expelled.
And then there was the flagrant category. The only infraction listed for a flagrant citation was moving a campus police barricade. So, if you had to make a choice between hitting a barricade or a jaywalker, you chose the pedestrian every time -- you got two of them for each barricade.
About the author
Donald J. Wheeler is an internationally known consulting statistician and the author of Understanding Variation: The Key to Managing Chaos and Understanding Statistical Process Control, Second Edition. He may be reached via e-mail at firstname.lastname@example.org.