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Last week a new study was published describing the results of a survey of the English general  population asking them “What causes cancer?” (direct link to open access paper). That’s  technically not what they asked, but you get the idea. The study made the national news, and  may have reached an international audience as well, and for example was covered by the BBC  as follows “Fake cancer causes belief 'rife', research suggests” (link). That doesn’t look great, so let’s have a closer look at this. First, what was actually asked was the following “How much do you agree that each of these  can increase a person’s risk of developing cancer?” for a selected set of things that could  cause cancer (or not). With the answer on a 5-point Likert scale (Likert famously invented  answering a question with ‘strongly disagree’, ‘disagree’, ‘unsure’, ‘agree’, or ‘strongly  agree’….genius). That is a reasonable question to ask, and that information is quite useful in  itself. What are people worried about in relation to their chance of developing cancer.  Alas, the authors then split the selected potential risk factors in two different sets: 11 that  have been proven to cause cancer  and 12 that are thought to cause cancer but, according to  the authors, do not. The first group includes active smoking, passive smoking, any alcohol  consumption, low fruit and vegetable consumption, being overweight, sunburnt more than  once as a child, being aged 70 years or older, having a relative with cancer, having an  infection with HPV, and low physical activity, and the second group includes drinking from  plastic bottles, eating food containing artificial sweeteners, eating genetically modified food,  eating food containing additives, using microwave ovens, using aerosol containers, using  mobile phones, using cleaning products. The latter group therefore, is called ‘mythical  causes’. Now I have a problem with the use of the term ‘mythical causes’ in a scientific paper. For one  thing, this places a judgement on the people who believe any of these could cause cancer.  But scientifically this is also nonsense for the simple reason it is not possible to prove a  negative. If that does not make sense, think about the following “are you 100% that not a  single food additive, in every product, in every country, at every point in time and in every  person may cause a cancer?” That’s just plain nonsense…for example, dyes derived from coal  tar may be added to foods.    You would now probably respond something like: “yes, but it is highly unlikely that food  additives would be carcinogenic and even if one would, you would eat so little of it this will  not give you cancer at all.” And if you would say that, you would indeed be correct. However,  that was not the question. The question was “How much do you agree that each of these can  increase a person’s risk of developing cancer?”, and the correct answer to this would be  anywhere from disagree to agree, but probably the best answer is ‘unsure’. Unfortunately,  ‘unsure’ according to the researchers this is always the incorrect answer .   It gets more confusing though. I won’t discuss each ‘mythical risk factor’, but just as an  example: ‘using mobile phones’ is also included. Of course the mobile phone itself does not  do anything, but let’s assume the authors meant exposure to radiofrequency radiation. This is  classified as ‘possibly carcinogenic to humans’, or 2B, by the WHO International Agency for  Research on Cancer (IARC), which was supported by the largest human study [Interphone]  done to date and which showed some possible evidence of increased risk in the highest  exposed group (reference). Other studies have been published, but most importantly recent  randomized and controlled animal studies have further provided evidence of carcinogenicity  (reference 1 and 2). Is this conclusive of a causal risk factor for cancer? No. Is the likelihood  of getting cancer from RF large? No. Does it unambiguously exclude RF as a cancer risk factor,  also no………So again, the correct answer to the question should have been ‘unsure’. For comparison, if we look at the “real cancer causes” side of the divide, for example a  ’relative with cancer’ is included. This is of course not a causal risk factor: your relative does  not give you cancer. This is a correlation from shared genetic and/or lifestyle and  environmental factors (interestingly, race, another such genetic factor, is not included). ‘Sunburn’ is included, which is not the causal factor, that would by UV radiation. And more  specifically, this refers to exposure beyond a certain threshold: a bit of sunshine does not give  you cancer. Again looking back at the ‘mythical causes’, in theory one could drink so much  from plastic bottles as to get a carcinogenic dose of dioxins and BPA (reference) [although this is not advisable to try, as you’d die from the amount of water you drank well before that]). An  alcoholic drink once every so often will not give you cancer either, and although “old age” by  itself increases the risk of cancer, it is not switch that when you turn, say, 70, the probability  of developing cancer is massively different from when you were 69, or 71.   So basically what we are looking at here, is a scale with implicit assumptions about where on  the carcinogenic exposure-risk we are for each risk factor. This differs between risk factors,  and people who were interviewed were not told this.        Note that apparently this is a validated scale, but because the methodology paper is not  published we have no idea how this was developed. So where this dichotomy of real and fake  causes is concerned let’s just ignore the scale. That does not make this a bad study though, if only the focus had been different. Had the  research question been “Does the general public focus on the most important cancer risks?” it  would have been great. Implicitly this is what the researchers did, they just aimed for an  easier to understand, more mediagenic, kind of approach. If we look at it from that perspective, this is actually a  good study. It is also a pretty sobering study… If you were under the impression that most people  know what is healthy and what is unhealthy, at least in  principle....  Most worryingly, the fact that 88% of people correctly  identified tobacco smoking as a cause of cancer implies  that for 12% - about 1 in every 10 people! – this is  completely new information! It is beyond me how  anyone could have missed that memo, but clearly this  is the case for a significant number of people. There is some indication of why this may be, in that  people who engage in unhealthy behaviour seem to  downplay the effect of their own behaviours, but  nonetheless it remains worrying. Where about 1 in 10 people had no idea smoking tobacco causes cancer, 7 in 10……let me  repeat that…7 IN 10! Had no idea that not eating fruit and vegetables increases your cancer  risk. Similarly, about 6 in 10 had no idea insufficient physical activity is a risk factor for  cancer (although a higher proportion, 6 in 10, did know obesity was).  For 4 in every ten people the fact that sunburns are a bad idea (aside from the acute pain) is  news ?! That explains quite a lot... These data really put a spanner in the whole libertarian “government back off, we know what  is good for us” red herring argument, doesn’t it. Again, I find these numbers absolutely astonishing, and much more important than whether  people also believe other potential, but definitely less important, risk factors may also  contribute to their cancer risk. If you think about the implication of the latter by itself,  reducing your stress levels, reducing the time you use your mobile phone or avoid physical  trauma is not such a bad idea regardless*.
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Ah Man! Does that cause cancer too?!
* the implicit assumption of dividing the scale in real vs mythical causes is of course that people who believe the less important factors are important, may focus on these and not engage with the much more important ones. There does not seem to be much evidence that this is the case though…
I don’t really know if this is true, but it fitted well with the article.