Lead in chicken broth?

After the lead and crime article in Mother Jones last month, I've been more aware of lead in the environment.  Perhaps that is why a paper finding lead in organic chicken stock in the journal Medical Hypotheses alarms me, at least slightly and hypothetically.  The researchers found concentrations of 9.5 mcg/L and 7 mcg/L, still below the EPA's "action level" of 15 mcg/L for drinking water, but the EPA in the same publication says that no concentration of lead is acceptable:  i.e., the goal level concentration is zero. 

As is the nature for a hypothesis-generating publication, the study used only one batch of chicken stock of each type:  one with bones, one with skin and cartilage, and one with meat.  Perhaps they picked a bad chicken, or perhaps it is only chicken from the UK.  It's impossible to know without more tests.  People always ask us statisticians what would have happened if the sample size would have been larger, and it's important to remember that we're statisticians, not fortune-tellers:  we can't know what results would have been without having the actual results.  It's strange and frustrating that with 3 authors on the paper, they couldn't be bothered to get a few more chickens to test.  At least they did a control of plain water boiled for the same period of time, which found near-zero concentrations, under 1 mcg/L.  (Chicken meat broth by contrast was just over 2 mcg/L.)

The authors neglected to mention that the technique of saving bones for stock from every piece of meat you eat is almost universally recommended by cookbook authors including Melissa Clark and Nigella Lawson, to ensure that you always have stock available when it's called for.  Cookbooks say that there is no substitute for stock, and if you don't have stock around, use water rather than canned.  It's disappointing that there might be dangers from what is considered a best practice for cooking, not to mention one that I've just started following myself!  The lentil soup made from homemade beef stock was amazing, and one guest told us that he'd never tasted anything like it. 

I will still use the chicken stock in my freezer, but I'd be reluctant to continue this habit if pregnant or if I had children, given how dangerous lead is during critical formative periods. I do wish that the authors had gotten their act together to get at least an n=10 from geographically dispersed chickens.  How hard would that have been, seriously? 

The importance of specific health communication

Often people speak in general terms about the negative effects of smoking. Here's a highly specific risk: smoking at the time of breast surgery can cause nipples to fall off. When the doctor warned his patient in general terms, she didn't really listen. When he told her specifically that her nipples might fall off if she kept smoking, she said she had the motivation to stop right away. That's a very important lesson for health communication in general, but also hard to implement because when public health campaigns do show very specific things that can go wrong, there can be accusations of scare tactics, whether it's showing very specific problems from STIs or very specific problems from smoking.

What's the line between a scare tactic and effective communication?

Chemicals and comparison groups

Current legislation is trying to ban a plastic that has been used for 50 years to line cans, so I decided to look into how much evidence there is that this plastic is dangerous, and whether the potential substitutes for this plastic are safe. The American Council on Science and Health finds little evidence that this plastic is dangerous; they find no proposals for what plastics might substitute, much less any evidence on the alternatives' safety profiles. Their analysis raises very good points and is worth reading.

Just as in statistics, the important question for any risk analysis is "compared to what?" Nothing is dangerous on an absolute level: risks always have to be weighed against their alternatives. When we banned DDT decades ago, it may or may not have had beneficial effects for the eagle population, but malaria has rebounded: going from millions of cases in Sri Lanka to a couple dozen, and then back up to a million cases after the DDT ban. Malaria still affects hundreds of millions of people around the world, many cases that might be prevented if DDT spraying were allowed. The developed world has not had malaria since the 1940s --- perhaps if malaria had rebounded, perhaps we would see pesticides as the life-saving tools that they are --- but we do have the resurgence of bed bugs, even on the Upper East Side, after they had been almost completely eliminated 50 years ago. Maybe the good effects of the DDT ban are worth hundreds of millions of cases of malaria in the developing world and bedbugs in the developed world, but alternatives always need to be considered. The WHO has backed bringing back DDT because it was so useful.

With the current talk of banning BPA, the comparison group is completely missing. By banning a plastic without discussing alternatives and their risks, we risk having worse alternatives or no alternatives.

Why doctors need to know Bayes theorem

In graduate school, I was the head TF for several general audience statistics courses, and my favorite subject was Bayes theorem because it implies that many "common sense" policies are, in fact, dangerous. Given a dreaded disease, drug use among ship captains or pilots, or anything else, it's so easy to say, "Just test everyone." But in fact, that's not good policy.

Social psychologist Gird Gigerenzer's new book covers some instances of asking doctors to give probabilities to their patients, and they do a horrible job. The question presents the information exactly as doctors are taught: prevalence, sensitivity, and specificity (false positives).

The probability that one of these women has breast cancer is 0.8 percent. If a woman has breast cancer, the probability is 90 percent that she will have a positive mammogram. If a woman does not have breast cancer, the probability is 7 percent that she will still have a positive mammogram. Imagine a woman who has a positive mammogram. What is the probability that she actually has breast cancer?

A prestigious doctor, department chief with 30 years of experience "was visibly nervous while trying to figure out what he would tell the woman. After mulling the numbers over, he finally estimated the woman’s probability of having breast cancer, given that she has a positive mammogram, to be 90 percent. Nervously, he added, ‘Oh, what nonsense. I can’t do this. You should test my daughter; she is studying medicine.’ He knew that his estimate was wrong, but he did not know how to reason better. Despite the fact that he had spent 10 minutes wringing his mind for an answer, he could not figure out how to draw a sound inference from the probabilities."

And he was typical: more than 90% of the doctors were wrong, mostly very wrong.

When the question was posed in terms that are easier for people to understand, nearly all of the doctors got the question right.

Is the Pill worth it?

Birth control pills are the default contraception method to such an extent that many people use the word "contraceptives" to mean birth control pills to the exclusion of all other methods, not realizing that diaphragms, condoms, sponges, IUDs, and withdrawal, among others, also count as contraceptives.

Birth control pills come with a raft of side-effects including weight gain, depression, and potentially fatal blood clots (such as deep vein thrombosis and strokes), but their popularity seems to improve their perceived safety. A new book looks at the risks of birth control pills, given the big and small health risks of them.

Of course this view is not new at all. The Boston Women's Health Collective famously recommended in Our Bodies Ourselves using barrier methods only: you know exactly what they're doing and their effects end once you remove them from the body. The ultimate transparency. Plus they prevent STDs.

Unfortunately barrier methods besides condoms are rarely used: diaphragms are used by less than 1% of contracepting women and the only company making the cervical cap discontinued it due to lack of demand.

Perhaps this book will convince some of its readers into looking into barrier methods instead. Plus condom plus diaphragm is at least as effective as the pill in typical use. (Here's the math: effectiveness of each alone is 80% in typical use, so effectiveness of both together is 96% (1-(1-.8)^2=.96), which is better than the 94% typical use effectiveness of the pill cited in the article.)

Flu risk perception

My understanding about the 1918 flu is that the first wave had few deaths, and those deaths followed standard pattern of seasonal flu: elderly and very young. The second wave came several months later and was a slightly changed form that had higher mortality, mostly in the healthiest age group, ages 20-40. These people didn't get it the first time around, so they were vulnerable in the second wave when it was more dangerous.

My question: is it possible that all these extreme measures such as closing schools --- e.g., Harvard closed down medical, dental, and public health schools today because of a case in the dental school --- will make the flu epidemic worse rather than better by inducing precaution fatigue and decreasing credibility of preventative measures such as vaccines and shutting down institutions so that when the flu is really serious people will assume it will be low mortality as it is now?

If this follows pattern of 1918, by the time the second scary wave of flu comes around, we will have a vaccine, perhaps even in adequate numbers to cover much of the population, but there's no vaccine for human irrationality. Everyone is getting all fired up now --- lots of parents kept their kids home at a local school here in suburban Baltimore due to 1 case in the school.

When the same thing happens next October or November, will people reason it's not important to be careful since last time turned out okay? Will people not bother to get the vaccine?