(Editor’s intro) From time to time we will have guest bloggers. For the first I am pleased to introduce Bill Roege, Director, Corporate Safety Analysis, DOE. Bill is a retired U.S. Air Force officer and fighter pilot. He is also a mathematician and an Ops Researcher. He is a graduate of the United States Air Force Academy and the Massachusetts Institute of Technology. Before joining DOE Bill was involved with leading edge performance analysis for the Pentagon. After joining DOE he became an advocate of HPI and High Reliability since he was familiar with much of the science behind these concepts and personally knowledgeable of the high reliability practices necessary to lead in the modern Air Force. Thanks to Bill for this blog!
The HPI “Performance Improvement Formula” and Mathematics
By William H. Roege
An important concept in Human Performance Improvement (HPI) literature is captured in the performance improvement formula: Re + Mc → ØE. In plain English, reducing errors (Re) coupled with managing controls (Mc) leads to zero significant events (ØE) (DOE Human Performance Improvement Handbook, Vol. 1, pg. 1-16). This simple, common sense formula is very appealing and useful to most people. However, to the mathematically inclined using even simple mathematical symbols implies a precision that does not exist and is therefore confusing. Instead of facilitating learning as intended, the formula becomes a barrier.
I believe the formula has two characteristics that give the mathematician trouble. First, adding two terms implies they independently contribute to the result. In this case, if one succeeded in driving errors to zero, there would still be many significant events if Mc were some positive number. Instead, these terms intuitively interact. That is, errors combine with the inadequate controls to produce events. In mathematics interactive terms are multiplied (or divided). They give each other leverage or are catalysts.
Second, I find the term “managing controls” is counterintuitive. My intuition says that more or better managing is good, but the current formula implies that would lead to more events not fewer! How should one think about Mc if it is small? I propose a slightly altered meaning for the Mc term to: “maximizing control effectiveness” thereby making large Mc very good.
Combining the two changes, I propose an alternative performance improvement formula that may appeal to the mathematician and non-mathematician alike: Lim Re/Mc → ØE. That is, one approaches zero events by reducing errors and maximizing control effectiveness. This recognizes that errors will never be zero and that control effectiveness can never be infinite, but by making one small and the other very large one can get very close to zero (many “9’s” in quality-speak).
Finally, I think it is important to communicate that Re and Mc are actually complex, non-linear functions with multiple variables. Indeed, humans are in the loop and there are no known closed form formulas that describe human behavior. The best one can do is use heuristic tools designed to help identify and correct undesirable situations.
Extending the Concept to High Reliability Organizational (HRO) Theory
Rick Hartley at Babcock & Wilcox Pantex is working to extend the performance improvement formula using High Reliability Organization (HRO) concepts. Pantex uses a notion they call a “work perception gap”—basically the difference between work as imagined as opposed to how work is actually done.1 When the two are not aligned the resulting gap can further complicate error reduction and control management efforts and lead to more significant events. This is a simple, but very powerful concept.
For this discussion, define Wi = work as imagined and Wd = work as done (each > 0); assume Wd can never be better than Wi (Wd ≤ Wi), so that the ratio Wd/Wi is always less than or equal to 1. Ideally, Wd/Wi would equal 1, but in the real world the ratio is going to be less than 1.
In order to be a good scaling factor in the performance improvement formula the new parameter must approach zero as it improves so it contributes to achieving zero events. A suitable parameter is then (1 – Wd/Wi). This parameter approaches zero as the work as done approaches work as imagined. Some may recognize an equivalent form is (Wi – Wd)/Wi or the difference between work as imagined and work as done scaled by the larger of the two, Wi.
I propose this new work gap scaling parameter and use the form “delta W” for the work perception gap:
ΔW = (1 – Wd/Wi) = (Wi – Wd)/Wi.
The new HRO form of the performance improvement formula then becomes:
Lim (Re/Mc) ΔW → ØE.
Minimizing errors and the work perception gap while maximizing control effectiveness will significantly lower the probability of significant events.
(Editor’s concluding comments) Jens Rasmussen, James Reason, Erik Hollnagel and others discuss “error” in cognitive terms relating to human information processing. It is in that sense that we use the term Re. Bill mentions the value of heuristics, and indeed there are a large number of tools that have been developed to support human performance. (see for example the DOE Human Performance Handbook Volume II)