Thinking About Risk

Kevin Drum preahces against the evils of teen tanning, which he follows with a conclusion that obviously Republicans are evil for opposing a tanning tax

Indoor tanning, on the other hand, is just plain horrifically bad. Aaron Carroll provides the basics:indoor tanning before age 25 increases the risk of skin cancer by 50-100 percent, and melanoma risk (the worst kind of skin cancer) increases by 1.8 percent with each additional tanning session per year. Despite this, the chart on the right shows the prevalence of indoor tanning among teenagers. It's high! Aaron is appalled:

This is so, so, so, so, so, so, so bad for you. Why don’t I see rage against this in my inbox like I do for diet soda? Why can’t people differentiate risk appropriately?

And who would fight a tax on this?

I am not going to get into the argument here (much) about individual choice and Pigovian taxes (by the way, check out the comments for a great example of what I call the Health Care Trojan Horse, the justifying of micro-regulation of our behavior because it might increase government health care costs).

I want to write about risk.  Drum and Carroll are taking the high ground here, claiming they are truly the ones who understand risk and all use poor benighted folks do not.  But Drum and Carroll repeat the mistake in this post which is the main reason no one can parse risk.

A key reason people don't understand risk is that the media talks about large percent changes to a small risk, without ever telling us the underlying unadjusted base risk.   A 100% increase in a risk may be trivial, or it might be bad.  A 100% increase in risk of death in a car accident would be very bad.  A 100% increase in the risk of getting hit by lightning would be trivial.

In this case, it's probably somewhere in between.  The overall lifetime risk of melanoma is about 2%.  This presumably includes those with bad behavior so the non-tanning number is likely lower, but we will use 2% as our base risk understanding that it is likely high.  The 5-year survival rate from these cancers (which by the way tend to show up after the age 60) is 90+% if you are white -- if you are black it is much lower (I don't know if that is a socio-economic problem or some aspect of the biology of darker skin).

So a teenager has a lifetime chance of dying early from melanoma of about 0.2%.  A 50% increase to this would raise this to 0.3%.  An extra one in one thousand chance of dying early from something likely to show up in old age -- is that "so, so, so, so, so, so, so bad"?  For some yes, for some no.  That is what individual choice is all about.

But note the different impacts on perception.

  • Statement 1:  "Teen tanning increases dangerous melanoma skin cancer risk by 50".
  • Statement 2:  "Teen tanning adds an additional 1 in 1000 chance of dying of skin cancer in old age."

Both are true.  Both should likely be in any article on the topic.  Only the first ever is included, though.


  1. Joshua Vanderberg:

    And lets not forget, what about the offsetting benefits of the added vitamin D? Many white northerners are vitamin D deficient, which might be linked to higher cancer risk for certain types of cancers.

  2. lelnet:

    Actually my guess would be that most of the improved survival odds for white people would be attributable to the fact that melanomas are more likely to be diagnosed early enough for effective treatment in white people. Because, you know...they're harder to miss, when your skin is pale, than they are when it's dark.

  3. NRG:

    Having lost two dear friends to Melanoma I have developed some observations.

    #1) most (nearly 100%) of melanomas show up first in places the sun never shined. (armpit, taint..) This alone seems to indicate sunshine is PROTECTIVE from melanoma and not a cause.

    #2) There are Australian studies that showed an overall increase in the skin cancer rate in Australia AFTER the invention of sunscreens as compared to the same population rates before sunscreens were introduced. This also seems to indicate sunshine is protective of skin cancers or that removing the body telling it's owner to get out of the sun (sunburn) allows for the cancers to develop.

    @Joshua seems to be spot on with my observations.

  4. Sam L.:

    Is Kev eating healthy? Does he drive to fast? Or too slow? Betcha he needs to be taxed for a number of things.

  5. Maximum Liberty:

    I suspect there is a hidden variable that actually explains much of the increase. People who go to tanning salons are probably the same people who, if tanning salons did not exist, would lie out in the back yard. Whether the tanning salon increases or decreases risk compared to lying out is facilially ambiguous. The tanning salon allows finer dosage control, which presumably lowers severe burns. But it also allows year-round tanning. Etc. That's not the same problem identified in the post, but missing it is just as naive.

  6. MingoV:

    The risk data is highly flawed. All of the studies were metadata analyses (extracting data from previously published studies), one of the least reliable study methods. The Stanford University School of Medicine study on tanning and non-melanoma cancers was based on studies going as far back as 1966. Tanning beds have greatly improved over the decades. They use less intense light, and they filter out UV light that isn't needed for tanning. I believe that modern tanning beds do not greatly increase skin cancer risks.

    The other two studies were of British and French populations. I do not know the quality of their tanning beds over the decades, but I expect that they were similar to the ones used here.

    Bottom line: These studies are biased, inaccurate, and overestimate the cancer risks from tanning beds.

  7. Shane:

    @MingoV, please post this information on The Incidental Economist. The more information the better.

  8. Shane:

    @NRG please post this on The Incidental Economist.

  9. obloodyhell:

    }}}} increases by 1.8 percent with each additional tanning session per year.

    1.8%... per session.... per year?

    So if I have 120 tanning sessions over 2 years time, my melanoma risk goes up by 200%?

    I'm betting if it was actually THAT bad that they could justify shutting the @#$#@$#@% things down, period, screw "taxing" them. If there was something in a soft drink that increased peoples' cancer risk by 200% in 2 years they'd shut that sucker down in a heartbeat.

    And it's the exact same if I do 12 sessions a year for 10 years? THAT seems unlikely to be either The Same Risk, OR to even be in the same ballpark.

    So ... someone's probably lying, misquoting, or otherwise twisting something, methinks.

  10. JoshK:

    Just a side note, I made the mistake of going to the Mother Jones site and lookingat the comments. There are a few poeople there who raise objections similar to what you discuss here. The sad thing is that you see the immediate angry ad hominem attacks. I think it hints at something very scary there under it all that I think goes beyond the issue itself.