I got to see the greatest of all sporting events, Game 7 of hockey's 2006 Stanley Cup Finals when the Carolina Hurricanes defeated the Edmonton Oilers 3-1 in front of the home crowd. The franchise had effectively mastered the many input variables for one fleeting season and produced the ultimate output. A fan of both AC/DC and the Scorpions, the pre-game warm-up song "Long Way to the Top" and introduction theme song "Rock You Like a Hurricane" will forever be emblazoned with new and special meanings.
Then, for over a decade, the peace and serenity of the eye of the storm proved elusive – the Hurricanes organization simply could not take care of the things that matter most.
Under new leadership over the past few seasons, the Hurricanes once again rose to the top of the National Hockey League, under new leadership and by focusing on what matters most.
Tornado diagrams are modified versions of a bar chart. They are a classic tool used to communicate the results of a sensitivity analysis, which can be performed either deterministically or probabilistically. The tornado diagram receives its name from the visual image created from wider bars associated with input variables that have more impact on the output being located at the top. In contrast, the narrow bars associated with input variables with less impact on the output are shown at the bottom. (You guessed it, I would have called them Hurricane diagrams.)
It is important to explain a Tornado diagram initially to decision makers. I have found the following sequence to be effective: the input variables are shown down the left side of the diagram; the vertical line running through the center of the bars represents central tendency (usually the median). The bars represent the potential range of variation from the vertical line (central tendency) resulting from that particular input parameter. The input parameters at the top of the diagram are much more important than those at the bottom of the diagram.
From practical experience, most decision makers quickly understand the primary takeaway—things at the top of the diagram are much more important than things at the bottom—after one explanation. It becomes a powerful reference graphic in projects with subsequent phases. It will also be a graphic that will become requested as a standard in other types of reliability, risk, and resiliency projects.
I want to note some practical considerations for presenting Tornado diagrams. First, the initial explanation of the Tornado diagram can be done in a picturesque manner, meaning that all the input parameters on the left side of the figure do not have to be legible by the audience. It is much more important for decision makers to understand the basic concepts and feel of the "tornado." Subsequent enlargements can drill down into the details of inputs that are most or least important; of course, in the case of enlargements, the inputs parameters should be legible.
Second, tornado diagrams are busy diagrams. Shades of black and blue colors are best for the major components. Use sharper colors like greens and reds to highlight key points.
Lastly, decision makers often initially understand them better than their technical advisors. For some reason, mathematical types want to drill down too fast. They want to get wrapped up in the trees without first soaking in the essence of the larger forest. Trust your decision makers and trust your Tornado diagrams.
Tornado diagrams are extremely powerful. They are among six essential graphics that should be included in communications with decision makers. You are leaving much value on the table if you are not regularly using Tornado diagrams.
The illustration "Tornado Diagram" and excerpts from this article are taken from JD Solomon's book, “Communicating Reliability, Risk and Resiliency to Decision Makers: How to Get Your Boss’s Boss to Understand.” The second edition will be released in June 2022. Sign-up for updates at Communicating with FINESSE.