At nearly every medical examination they measure your height and weight. These two numbers are then combined to work out your Body Mass Index (BMI). It is one of the KPIs used to assess your health. If your score is 25 or higher you are overweight, if it is higher than 30 you are obese, 35 and you are clinically obese etc.
Medical insurance companies require their customers to have regular health check ups. They use BMI as an indicator of whether you are overweight or even obese. And this affects your premium and potentially whether they will continue to offer you insurance. A friend of mine recently came out at 25.0 (just overweight). Removal of keys and wallet and it was down to 24.9 and all was OK.
A couple of years back I met a fireman with a BMI of 27.3. He told me how he'd got a written warning from his employer for being "over weight". He had to get his BMI below 25 before his next medical. Failure to do so would lead to a final warning and then if no improvement to dismissal*. Nobody would disagree that firefighters need to be fit but that seemed harsh.
A brief history of BMI
In the 1840s, a Belgian scientist (Adophe Quetelet) noticed a correlation between body weight and the square of height. Over a century later, in the 1970s, a social scientist (Ancel Keys) realised that this could be a good way of tracking changing levels of obesity over time and across populations. The WHO now use BMI to assess nutritional health across countries. Your doctor uses it to determine whether you are over or under weight.
A bit more on the two examples above
The fireman I was talking to competed in 3-4 Iron Man races a year. These are super triathlons with a 2.4 mile swim, a marathon (26.2 miles) and a 112 mile cycle ride. He was one of the fittest people I've met. The friend I mentioned is a strong fit cyclist. Another cyclist, Sir Chris Hoy, had a BMI was 27.2 - which put him as over weight.
Then there is Steve Redgrave who at his physical peak had a BMI of 29 - borderline obese. When Arnie was Mr Universe his BMI was 31. A lean and fit Tom Cruise came in at 32!
BMI fails in these cases because muscle weighs about 20% more than the same volume of fat and of course athletes carry more muscle than the rest of us. BMI also struggles with tall or short people. It remains a useful indicator for comparing sedentary people who are of average heights. As Keys himself said - BMI is appropriate measure for population studies but inappropriate for individual evaluation. So in many ways BMI is a flawed measure.
How does this link to KPIs?
The above is an example of how we can get KPIs wrong. We know our fireman was more than fit enough to perform his role. That is what the Fire Service were trying to assess. Yet you can see how the use of BMI as a measure of how over weight he was could have led to his dismissal.
KPIs are Key Performance Indicators. The clue is in the word "indicator". An indicator is an indicator, it is not the same as what you want to manage/improve. A staff satisfaction survey is not the same as staff satisfaction. Top of mind recall is not the same as brand health. BMI is not the same as % body fat.
Body fat % is not that easy to measure. Height and weight are. We can be confident of the accuracy of BMI numbers whether they come from Sweden, Switzerland or Somalia. That is why the WHO uses BMI when comparing countries. And, as we have seen, for looking at populations it is not a bad measure. The danger comes when we try to use it to tell us someone is overweight or obese. And even worse if their insurance premium goes up or they lose their job as a result.
Secondly as soon as a KPI becomes a target it ceases to be a useful measure. Sometimes you end up getting the opposite of what you want! People smarter and with more time than you or me will find ways to hit a KPI target. Often in ways which achieve exactly the opposite of what you intended. You want to use BMI to assess how fit I am? No worries. I won't eat for a week or I'll sit in a sauna to dehydrate myself before I'm measured (we are about 60% water). That will get my weight and thus BMI down to where it needs to be but at some cost to my health. Boxers can do real damage dehydrating themselves to "make weight".
And finally the thing you want to improve with your KPI should link to your strategy. In the case of BMI, body fat is a component of health or the level of obesity in a society. So if you want to know whether a society is getting fatter or less healthy measuing body fat % is the right thing to do. If you were training to be an Olympic rower it would not only be a poor measure but it could actually cause you to be a worse rower. It has little or no impact on your performance. Power through the water, how long you can maintain it or VO2 Max would be far better measures.
So if you are introducing KPIs or have KPIs in your organisation make sure that:
1) You are clear what success looks like and what you need to make happen to achieve that success (your critical success factors). In the above example body fat % is an important component of fitness.
2) You don't confuse the indicator with the the thing you are trying to improve. As we have seen they are not the same thing. Indicators will always have limitations. In this example BMI is not the same as body fat %.
3) You avoid the temptation to use a KPI as a target (or even worse a basis for rewards). As soon as you do that the KPI ceases to be a useful measure because people will either manipulate the figures or optimise that KPI often at the expense of your original intention.
Review your KPIs to see whether they satisfy these three tests. Get in touch if you are thinking about introducing KPIs or wondering why the ones you've got are not working.
*Fortunately the UK fire service has dropped this measure and now uses genuine and appropriate tests of fitness for the job.