QUESTION: Can Rare Events Be Meaningfully Measured?

February 12, 2013 by Stacey Barr

Subscriber Nia B. asks: “We need to establish a measure for safety, however we have a terrific safety record and insufficient data to establish one. Is there a meaningful way to measure this?”

Most measures of performance are used to track areas that need improvement. But there is a case to measure things that are performing well. And areas like innovation, industrial disputes, hospital infections and safety performance are good examples: any movement in the wrong direction is something you want to know about, even if it’s not something you’re actively trying to improve.

But when things like safety are going well, they’re not producing any data to monitor! You might get one accident every year or so. And that makes for a stupid-looking and very sparse bar chart.

So you end up resorting to next-to-useless measures like Number of Accidents or Number of Near Misses or % Staff Attending Safety Induction Training as evidence of success. But the success is evidenced by the absence of data, not the substitution of quasi-correlated data-abounding proxies!

The solution is to convert this absence of data into something more informative. You have two very simple and sensible options.

Option 1: Measure the number of days between accidents

What you compute for your measure’s value here is the number of days between accidents. The most recent measure value will be the number of days since the last accident.

A good result is when the days between accidents is larger. But with this kind of measure, it’s a little trickier to pick up signals of change easily. So Option 2 works a bit better.

Option 2: Measure the accident rate

What we do is turn our count of safety accidents into a rate of accidents per time period. It doesn’t have to be annual: the idea is to think about the rate value as opposed to the count value.

The data that you are actually collecting is the date on which the accident happened. You’ll use this raw data to calculate the rate by first working out the days between accidents, as in Option 1. Then, using the days between accidents, compute a value of the number of accidents per day by simply inverting that value (dividing it into 1). That gives you the accident rate.

Then you can use your accident rate on a Smart Chart, the absolute best kind of chart for highlighting REAL signals in your performance measures.

Find out what a Smart Chart is here: //

Or learn how to create Smart Charts, step by step, here: //


Are you getting enough sense out of your measures of rare events? Find 30 minutes and a cup of coffee, and give the incident rate method a try. The Using Smart Charts course includes a template for how to convert your rare event data into an incident rate, and reveal signals by using a powerful Smart Chart.

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  1. Pål Navestad says:

    Om measuring rare events as safety. You suggest to use rate instaead of counts or days between. However when accidents become few you again do not gain that much from calculating rates. It is still a sparse graph and when cahnges happen there will be abruptness. Using Smartcahrts is really not that usefull neither since the bands by necessity become very broad. All sorts of rolling avareages etc. also get the jump when accidents happen (and in rolling averages jump when they go away). Hence I think it is best to just count and show the events. Number of days since last event usually has great PR value.

    You commented upon “stupid” measures as % attending safety briefings etc. Safety, quality and event avoidance has clear ties to culture. Do You have any suggestions on how to measure culture changes in a good way? We have some experience with the so called “stupid” measures and do think that they can help improve culture, but have no way of being certain.

  2. Stacey Barr says:

    Pal, it could be that safety accidents is no longer a high priority to measure. Rather, you’d start to monitor some proxy measures, or lead indicators, like near misses (an event that would have been an accident if the hammer fell 1 inch to the left, so to speak) or opportunities for accidents (the hammer is sitting on the bench with the handle hanging out which someone could easily knock down). These are more meaningful than attendance at safety briefings. What would you prefer: more people coming to more meetings, or fewer hammers lying around instead of hanging on their hooks?

  3. Mark Gandy says:

    I’m reminded of the person that has lost around 45 pounds and has kept if off for more than 3 years–that person is me.

    In my scenario, like the days since lost time incident, there is minimal variation (my desired weight) over time.

    But I still have to track training time, diet, and sleep. Those are my success habits (3 strength days, 3 intense cardio days per week, well-rounded 2600 calorie diet, 7.5 to 8 hours of sleep each night).

    Accordingly, the company above could also be tracking the 3 to 5 process measures that drive their product result (days since lost time).

    We both know there will be variation daily, weekly, monthly on those process activities giving the company insights on what area needs additional training, coaching, process improvement, etc.


    • Stacey Barr says:

      Mark, congrats on your personal success. Your example is a great one. I do similar things for my own health: measuring the success habits daily and the results of those less frequently. The same in business too. I’ve started measuring weekly habits in my work, that I know will drive the longer term outcomes I want.

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