A while ago I wrote a post about the practice of advertistics – the use, and more often misuse, of Statistics by advertising companies to promote their products. And I referenced an article in the Guardian which included a number of examples of advertistics. One of these examples was Marmite.
You probably know the line: Marmite – you either love it or hate it. That’s an advertisitic in itself. And almost certainly provably incorrect – I just have to find one person who’s indifferent to Marmite.
But I want to discuss a slightly different issue. This ‘love or hate Marmite’ theme has turned up as an advertistic for a completely different product…
DNAfit is one of a number of do-it-yourself DNA testing kits. Here’s what they say about themselves:
DNAfit helps you become the best possible version of yourself. We promise a smarter, easier and more effective solution to health and fitness, entirely unique to your DNA profile. Whatever your goal, DNAfit will ensure you live a longer, happier and healthier life.
And here’s the eminent statistician, er, Rio Ferdinand, to persuade you with statistical facts as to why you should sign up with DNAfit.
But where’s the Marmite?
Well, as part of a campaign that was purportedly setup to address a decline in Marmite sales, but was coincidentally promoted as an advertistic for the DNAfit testing kit, a scientific project was set up to find genetic markers that identify whether a person will be a lover or hater of Marmite. (Let’s ignore, for the moment, the fact that the easiest way to discover if a person is a ‘lover’ or ‘hater’ of Marmite is simply to ask them.)
Here’s a summary of what they did:
- They recruited a sample of 261 individuals;
- For each individual, they took a DNA sample;
- They also questioned the individuals to determine whether they love or hate Marmite;
- They then applied standard statistical techniques to identify a small number of genetic markers that separate the Marmite lovers from the haters. Essentially, they looked for a combination of DNA markers which were present in the ‘haters’, but absent in the ‘lovers’ (or vice versa).
Finally, the study was given a sheen of respectability through the publication of a white paper with various genetic scientists as authors.
But, here’s the typical reaction of another scientist on receiving a press release about the study:
I have just received the most unscientific, pile-of-shit press release I have ever seen. I feel dirty just having read it. Won’t give it PR.
— Kit Chapman (@ChemistryKit) September 6, 2017
Wow, sorry about the language there. So, what’s wrong?
The Marmite gene study is actually pretty poor science. One reason, as explained in this New Scientist article, is that there’s no control for environmental factors. For example, several members of a family might all love Marmite because the parents do and introduced their kids to it at a very early age. The close family connection will also mean that these individuals have similar DNA. So, you’ll find a set of genetic characteristics that each of these family members have, and they all also love Marmite. Conclusion – these are genetic markers for loving Marmite. Wrong: these are genetic markers for this particular family who, because they share meals together, all love Marmite.
I’d guess there are other factors too. A sample of 261 seems rather small to me. There are many possible genetic markers, and many, many more combinations of genetic markers. With so many options it’s almost certain that purely by chance in 261 individuals you can find one set of markers shared only by the ‘lovers’ and another set shared only by the ‘haters’. We’ve seen this stuff before: look at enough things and something unlikely is bound to occur just by chance. It’s just unlikely to happen again outside of the sample of individuals that took part in the study.
Moreover, there seems to have been no attempt at validating the results on an independent set of individuals.
Unfortunately for DNAfit and Marmite, they took the campaign one stage further and encouraged Marmite customers – and non-customers – to carry out their own DNA test to see if they were Marmite ‘lovers’ or ‘haters’ using the classification found in the genetic study. If only they’d thought to do this as part of the study itself. Because although the test claimed to be 99.98% accurate, rather many people who paid to be tested found they’d been wrongly classified.
One ‘lover’ who was classified as a ‘hater’ wrote:
I was genuinely upset when I got my results back. Mostly because, hello, I am a ‘lover’, but also because I feel like Marmite led me on with a cheap publicity tool and I fell for it. I feel dirty and used.
While a wrongly-classified ‘hater’ said:
I am somewhat offended! I haven’t touched Marmite since I was about eight because even just the thought of it makes me want to curl up into a ball and scrub my tounge.
Ouch! ‘Dirty and used’. ‘Scrub my tongue’. Not great publicity for either Marmite or DNAfit, and both companies seem to have dropped the campaign pretty quickly and deleted as many references to it as they were able.
Ah, the price of doing Statistics badly.
p.s. There was a warning in the ads about a misclassification rate higher than 0.02% but they just dismissed it as fake news…