What ‘Probably Causes Cancer’ Really Means

One of the most commonly-used pesticides in the world was recently declared a probable cause of cancer — but that doesn’t mean what you think. Here are some stick figures to explain it to you.

This video by Andrew Maynard of the University of Michigan’s Risk Science Center explains what exactly the word “probably” means in that context (it has a specific definition). It doesn’t mean that the substance is a carcinogen and it will probably give you cancer; it means that it’s probably a carcinogen that may or may not ever give anyone cancer. If that’s confusing, don’t worry; the stick figures will make it all clear.

Once you’ve watched that video, consider checking out the others from Risk Bites, including whether BPA is harmful, whether mobile phones are frying your brain, and whether or not it’s dangerous to eat green potato chips.

What Does “Probably Cause Cancer” Actually Mean? [Risk Bites]


  • One question I always have is why do these groups, in this case IARC, use language that they almost know for certain that the mass media & the conspiracy folk will jump all over and misuse to terrify the viewer?

    Surely they could come up with better definitions and wording to more accurately reflect what they mean and avoid using words which, when used in common usage, given an entirely different impression.

    When I hear “probable/probably” I think “this means if I am exposed to this it will likely cause cancer”.

    • It’s not the IARC’s fault that you don’t understand that ‘carcinogen’ means ‘substance which sometimes causes cancer’.
      Only a person unfamiliar with the concepts of dosage and exposure could conclude that the word ‘probable’ refers to your odds of getting cancer.

      World <> binary.

      • You’re obviously rather dense. This whole video was explaining what the word probably means in this context. I was asking why they use a term which is confusing for people to understand. Why not use a more accurate term?

        I didn’t say I didn’t understand the definitions of words. Your reading comprehension is woeful.

        • If the metservice say “probable cloud” do you hear “probable flooding”?

          Of course you don’t, because you know that the word ‘probable’ has bugger all to do with the seriousness of any resulting rain.

          A person of moderate intelligence may further conclude that there is bugger-all chance of flooding because the metservice would have been more likely to see it coming, and made a more emphatic comment!

          In precisely the same way, “probable carcinogen” means it’s probably a carcinogen.

          A person of moderate intelligence may further conclude that *if* it is a carcinogen, it’s a *weak* one because powerful carcinogens are easier to demonstrate so less-tentative statements are likely.

          The IARC’s use of probable is intuitive and clear. If you want to call people out for being dense, start with any english-speaking adult so irrational that when they hear “probable carcinogen” they conclude “if I am exposed to this it will likely cause cancer”.

          • Did you even watch the video? I am inclined to think you did not. Why does this video even exist if the context of probably in this case isn’t any different to the common definition?

            The common definition of probably is:

            adverb: probably
            almost certainly; as far as one knows or can tell.

            Which, if you bothered to watch the video or understand the whole point of it existing, you would understand is not necessarily what the word “probably” means when IARC says something “probably causes cancer”. The video has a scale which indicates what “possibly” and “probably” means when they evaluate the data to determine if something is a carcinogen.

            Again, you’ve misunderstood the entire video (assuming you even bothered to watch it), and a common English word.

            I’m probably not going to bother responding to you any further.

          • OK now I see why you’re confused, you don’t know you’ve been tricked.

            The IARC classification is ‘probable carcinogen’.

            For most of the video they claim the IARC classification is ‘probably causes cancer’.

            You didn’t notice the deception.

            The reason ‘probably causes cancer’ is so different from ‘probable carcinogen’ is in the probabilistic nature of the word ‘carcinogen’.

            ‘probable carcinogen’ means only that it’s unlikely there’s a zero chance of cancer causation.

            If you still don’t understand, I can explain about how nested probabilities work. I make the offer because many people make strange errors like assuming that if we don’t know something is impossible, then it is possible.

  • “When I hear “probable/probably” I think “this means if I am exposed to this it will likely cause cancer”.”

    *You* think this, but *I’m* dense…

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