Unable to grasp the meaning of numbers

by Leland Teschler, Executive Editor

Much has been written about the innumeracy of the general populace. An inability to grasp the meaning of numbers leads to a variety of bad outcomes that include a predilection to be hoodwinked by junk science and financial scams.

An even more pernicious outcome of an inability to understand simple math concerns evaluating every day risks. The case of an IKEA furniture recall may be a case in point. Under pressure from the Consumer Product Safety Commission, IKEA recently recalled 36 million dressers because in the space of two years, three children were killed when the furniture tipped over on top of them. Apparently the dressers were not anchored to the wall as per instructions from the company.


The dressers in question have been sold for 14 years and in that span of time have caused five deaths. Thus it is easy to figure what it will cost to prevent five deaths over the next 14 years: If the cost of recalling a single unit is $25 (a ballpark estimate), that means it would take $900 million to fix the 36 million dressers already sold, about $180 million per death.

Commentators have pointed out that though the deaths were tragic, they were also anomalies. Their point: treating all products like IKEA’s dressers puts society in the position of spending infinite sums to spare a diminishingly small number of lives. By logical extension, it is not rational to spend huge sums in an effort to make any product or activity 100% safe. Numerically literate people should be able to understand this.

Another example of people who can’t grasp the meaning of numbers arises in the debate about mandating sprinkler systems in homes. The International Code Council, which develops safety codes and standards, in 2009 came out with a code requiring new one- and two-family homes be equipped with sprinklers for fire suppression. States can choose to follow the ICC code or not, and seven of them have elected not to.

It is easy to see why. The journalism site ProPublica.org, writing about the sprinkler debate, recently said it reviewed real estate records and found two deaths and 37 fires that caused injuries in homes built since 2009 in the seven states where the sprinkler mandate has been blocked.

The estimated cost of a residential sprinkler system is about $1,500. That statistic gives a way to estimate what it would cost states not mandating sprinkler systems to prevent the two deaths and

37 fires you’d expect to see if the next seven years are like the last seven. The total number of single-unit building permits for the seven states in question from 2009 to 2014 is 893,782, according to the U.S. Census. The total cost of putting $1,500 sprinkler systems in those houses would have been $1.34 billion. Assuming a similar number of houses get built in the coming seven years, the bill for preventing an expected 37 fires would run $36 million per fire.

The ProPublica piece on sprinklers had an extremely pro-sprinkler tone. It quotes the president of the National Fire Sprinkler Association as saying, “As the (former) fire chief I had to drive past those houses (lacking sprinklers),….and I knew that some day there could be an event there that could cost somebody their life.”

Consider this comment in the light of traffic fatality statistics. There were 32,675 U.S. traffic fatalities just in 2014. Thus the NFSA president was in far more danger driving past homes lacking sprinklers than were the inhabitants who dwelled there.

Evidently this irony was completely lost on the ProPublica reporter.


  1. ALAN BRINSON says:

    Let’s continue the numerical analysis. Assuming the fires were spread over the seven years the average age of the home was 3.5 years. The editor has forgotten that those systems will continue to save lives. Sprinkler systems can be assumed to last for fifty years in a home (there are systems over 100 years old). Let’s make it 49 years to simplify the calculation. That’s another 14 batches of 2 deaths and 37 fires. The bill to prevent the fires is actually 36/15 or $2.4 million. This is well below the threshold for mandating a safety measure. If you are going to comment about math, get it right!

    • Thanks for writing. I don’t have a lot of space to work with in my commentaries and unfortunately, I couldn’t go into much depth on the topic of residential sprinkler systems and their shortcomings.
      With regard to your calculations, I would say your math is right but your reality is wrong. I’d submit that there are strong indications that residential sprinklers won’t provide protection over the 50-year span that you speak of. The reason comes from anecdotal evidence that many house fires that become serious do so because either there were no smoke detectors installed, or because those present weren’t maintained.
      The point is that house occupants who can’t be bothered to install new batteries in a $25 smoke detector aren’t likely to do any better maintaining a sprinkler system. A scenario likely to unfold is that most sprinkler systems in houses that are 50 years old will have only been tested during a house inspection accompanying a sale. If the occupants have had trouble with the sprinklers somewhere along the line, they may well elect to just turn off the whole system.
      And if the seller elects to cut the price in lieu of fixing a sprinkler problem, well, it is interesting to speculate how many home purchasers will actually spend the money to get the system working again. All in all, I like my numbers better than yours.
      If you are curious, I have no financial interest in any kind of concern that benefits from not mandating the use of sprinklers, nor am I part of any kind of special interest group that opposes such a mandate. I am just a guy with an opinion.

      • Tom Lindtveit says:

        I think the editor is looking for math that supports his opinion. There is a lot more to this than the very simple ‘numbers’ presented. Chief among these is that sprinkler systems have been clearly shown to reduce significantly the cost of damage caused by a fire, allowing the fire department time to arrive and do their job. As homes age, the number of incidents will rise, based on that age. These are no small details, but significant numbers. Having worked in, and given part of my soul to the Fire Service, and been involved in fatal fires, I can tell you first hand that pulling a child’s body from a burned out house can change your perspective about what the ‘real costs’ are in fire protection. For my money, that $1,500 is an absolute no-brainer expense and anybody who thinks otherwise is using bad math with their facts coming from the media, rather than science. But that’s just my opinion after reading dozens of studies, comprehensive statistics from the last 50 years, research, and test burn results, not to mention the hands on experience.

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