Just because I _can_ calculate something doesn’t mean I _should_

Like many other maths teachers, I was taken with the article in the Liverpool Echo with the headline:

I was invited for a covid vaccine because the NHS thought I was 6cm tall

A journalist for the Echo was surprised to be sent an appointment for a vaccine, despite being in his 30s without any major health concerns.  On asking why he received this invitation he was told that his height had been mistakenly entered as 6.2cm, which gave him a Body Mass Index of 28,000.  Given that a BMI of >40 is considered to be ‘morbidly obese’, this obviously put him at major risk!

As a Core Maths teacher, I was particularly excited, because this course (with UCAS points equivalent to an AS-level, aimed at sixth formers who aren’t studying A-level maths) includes a requirement for students to be able to analyse real uses of mathematics.  I wrote this up, intending to post it as part of my series of ‘Questions Inspired By A News Story’.  We can work out the mass of the journalist (and then his real BMI) because we are given the putative BMI and the height it was based on.  We can also work out that a 6-foot person with this BMI would weigh 94 tonnes!

I haven’t posted it because I feel a little uneasy.

• It’s personal: I would be encouraging the students to work out the weight of the journalist.
• BMI is a flawed measure.
• I worry my students will calculate their own BMI (even if I don’t want them to). This is problematic if there are students who want to be right on the bottom end of ‘healthy weight’ or who make errors in their calculations and suddenly think they are obese, etc.
• BMI is a population measure, and not an individual one, so we can’t interpret it for certain for each individual.

How might Core Maths teachers use this?

I think it is worth using as a cautionary tale about checking your inputs and your answers.  (Clearly it’s nonsense to have 6.2cm as a height, and clearly 28,000 BMI wouldn’t be feasible as an answer.) 

Aside from this, though, I don’t plan to use it to carry out other calculations with this in class, even though I can.