William M. Briggs

Statistician to the Stars!

Next prohibition: salt

Here is a question I added to my chapter on logic today.

New York City “Health Czar” Thomas Frieden (D), who successfully banned smoking and trans fat in restaurants and who now wants to add salt to the list, said in an issue of Circulation: Cardiovascular Quality and Outcomes that “cardiovascular disease is the leading cause of death in the United States.” Describe why no government or no person, no matter the purity of their hearts, can ever eliminate the leading cause of death.

I’ll answer that in a moment. First, Frieden is engaged in yet another attempt by the government to increase control over your life. Their reasoning goes “You are not smart enough to avoid foods which we claim—without error—are bad for you. Therefore, we shall regulate or ban such foods and save you from making decisions for yourself. There are some choices you should not be allowed to make.”

The New York Sun reports on this in today’s paper (better click on that link fast, because today could be the last day of that paper).

“We’ve done some health education on salt, but the fact is that it’s in food and it’s almost impossible for someone to get it out,” Dr. Frieden said. “Really, this is something that requires an industry-wide response and preferably a national response.”…”Processed and restaurant foods account for 77% of salt consumption, so it is nearly impossible for consumers to greatly reduce their own salt intake,” they wrote. Similarly, regarding sugar, they wrote: “Reversing the increasing intake of sugar is central to limiting calories, but governments have not done enough to address this threat.”

Get that? It’s nearly impossible for “consumers” (they mean people) to regulate their own salt intake. “Consumers” are being duped and controlled by powers greater than themselves, they are being forced to eat more salt than they want. But, lo! There is salvation in building a larger government! If that isn’t a fair interpretation of the authors’ views, then I’ll (again) eat my hat.

The impetus for Frieden’s latest passion is noticing that salt (sodium) is correlated—but not perfectly predictive of, it should be emphasized—with cardiovascular disease, namely high blood pressure (HBP). This correlation makes physical sense, at least. However, because sodium is only correlated with HBP, it means that for some people average salt intake is harmless or even helpful (Samuel Mann, a physician at Cornell, even states this).

What is strange is that, even by Frieden’s own estimate (from the Circulation paper), the rate of hypertension in NYC is four percentage points lower than the rest of the nation! NYC is about 26%, the rest of you are at about 30% If these estimates are accurate, it means New York City residents are doing better than non residents. This would argue that we should mandate non-city companies should emulate the practices of restaurants and food processors that serve the city. It in no way follows that we should burden city businesses with more regulation.

Sanity check:

[E]xecutive vice president of the New York State Restaurant Association, Charles Hunt…said any efforts to limit salt consumption should take place at home, as only about 25% of meals are consumed outside the home.

“I’m concerned in that they have a tendency to try to blame all these health problems on restaurants…This nanny state that has been hinted about, or even partially created, where the government agencies start telling people what they should and shouldn’t eat, when they start telling restaurants they need to take on that role, we think its beyond the purview of government,” Mr. Hunt said.

Amen, Mr Hunt. It just goes to show you why creators and users of statistics have such a bad reputation. Even when the results are dead against you, it is still possible to claim what you want to claim. It’s even worse here, because it isn’t even clear what the results are. By that I mean, the statements made by Frieden and other physicians are much more certain than they should be given the results of his paper. Readers of this blog will not find that unusual.

What follows is a brief but technical description of the Circulation paper (and homework answer). Interested readers can click on.

Friedman’s results
The paper is the result of a survey on hypertension. Surveyors ran around the city and asked just over 3000 people to participate. A little less than 2000 agreed to help a little, and only about 1700, or 55%, gave all the information requested. Incidentally, I don’t except anybody to take my word for any of this: download the paper and follow along with my summary.

If you know the city, you know it’s blocked off by neighborhoods that tend to, roughly, fall along racial and ethnic boundaries. The researchers knew this and correctly tried to sample by these blocks. They couldn’t get fair representation of this groups—meaning that, say there are known to be 12% of Group A residents in the city but the survey only could find 5%. It was also the case that the response rate varied by the blocks, which should add another “grain of salt” with which you read the results. Because of these factors, they decided to use a complicated weighting formula to adjust all their results. What you are seeing, then, are not the raw numbers. You are seeing the result of an error-prone statistical model. They say:

Analyses were weighted to adjust for the complex sampling design and nonresponse; weights were poststratified to represent the NYC adult population on age, sex, race/ethnicity, and borough of residence, then further adjusted to address component- and item-level nonresponse. SUDAAN version 9.0 (Research Triangle Institute, Methods Research Triangle Park, NC) was used to apply sample weights and to obtain standard error estimates by Taylor series linearization1.

The numbers were further massaged by what is called a logistic regression model. They “adjusted [their] models based on known risk factors, including age, race/ethnicity, sex, place of birth, education, income level, insurance status, and having a routine place for care.” This is not an unusual thing to do, but readers should be aware that they are not getting direct numbers, but instead estimates of parameters of statistical models.

Readers of this blog will recall that nearly all statistical procedures are designed to make statements about (unobservable parameters) and that probability statements regarding them will always be more certain than the actual observable data which they parameterize. The short way to say this is that if you leave any statistical analyses thinking only of parameter statements, you will be too sure of yourself.

Very well. The results, as pointed out above, found that NYC residents have less hypertension than non residents. They also found “disparities”, i.e. certain groups, ages, races, etc. had hypertension rates different than other groups etc. Apparently one such “disparity” is that Mexican-Americans have lower hypertension rates than do Dominican- and Puerto Rican-Americans. And more old people than young. Most of these findings are not new.

No social medical study worth its salt will publish a paper nowadays without pointing out “disparities.” I keep meaning to show you, my loyal readers, a calculation which shows that “disparities” are inevitable in datasets of sufficient size, even when nothing is going on. But that is a subject for another time.

The paper did mention several caveats and limitations, for which I applaud them. Here are some:

The present study has limitations associated with potential measurement error, survey response rates, and small sample size for subgroup analyses. First, although a clinical diagnosis of hypertension requires documentation of elevated pressures on 2 separate office visits, our measurements were collected in 1 sitting, which potentially could have caused us to overestimate disease rates…Another limitation is the 55% survey response rate. We addressed this potential selection bias through the use of survey weights that adjusted for information on age, sex, race/ethnicity, borough of residence, income, education, language spoken at home, and household size, obtained either directly from interviews or from neighborhood census data. Other potential sources of error include recall bias and measurement error…Another limitation is that the present model could not measure all aspects of access to care.

Now go back to the New York Sun article and see how many of these limitations and caveats made it into the story, and into the decision making process of Frieden.

———-
1“Taylor series linearization” sound fancy? It isn’t. Anybody who has ever had calculus will recall that this procedure “cuts off all higher order terms” to make an approximation that is easier to compute than the original problem, meaning—surprise!—that the results will be more certain than they should be.

Homework answer

Given that everybody will die, and that all effects have a cause, everybody will die of some cause. In any period of time you consider in which there are at least some deaths, those deaths will therefore have various causes. One (or more) of these will outnumber the other causes. This cause (or group) will be called “The Leading Cause.”

It is not a question of logic whether seeking to change the current leading cause to another one is good.

19 Comments

  1. Your homework assignment puts me in mind of all those newspaper stories that say, “such-and-such new wonder drug reduces deaths by 30%.” Since everyones’ chances of death are 100% in the long run, those kind of statements make no logical sense.

    Usually, of course, what’s missing is the time frame over which the effects are measured.

  2. if i chose to smoke, it should be an informed decision. if i chose to overload on calories, it should be an informed decision. if i chose to not exercise, it should be an informed decision.

    the highest and best role of government is to ensure that the information is available. they can disseminate the information directly, or allow tax breaks for companies that make the information available (non-profit groups, tax deductions for R&D expenditures). these things are being done – perhaps not well, but done.

    for the government to now step in and mandate the food i consume is an absurd expansion of privilege. and that is what it is – a privilege, not a right. the government exists solely for our benefit. they lose sight of their assigned role constantly.

    MSG does not sit well with a lot of people that enjoy chinese food – so ensure that restaurants declare its use. that’s it. no more. help me make an informed decision. then leave me alone.

  3. Personally, I’m a big fan of the detailed calorie advertising that is required in Manhattan. I don’t really count calories that much, but it’s nice to know the information is there.

    As for salt reductions… wouldn’t having people get off their tuchuses and move around be more effective at lowering BP than reducing sodium intake?

    Call me crazy, and I may be grasping at straws here, but doesn’t the fact that most New Yorkers move around more than most of the rest of the nation (as in walking) probably play more of a role in BP than sodium intake?

    But what do I know, I’m not a physician…

  4. I thought the leading cause of death was old age. Don’t know how lifestyle alteration will change that. Several years ago I saw a study that concluded that lifestyle changes have little effect on longevity.

  5. Briggs

    September 29, 2008 at 1:00 pm

    Ray,

    You make an excellent point. However, when you finally crap out, the official form won’t list a category for “old age.” Officially, that doesn’t exist and cannot be (easily) tracked.

    Some other cause will be written in. It may be old age, of course, but whatever part wore out first will get the blame. And if the docs can’t guess, they will fall back on percentages and say something like heart failure.

    Ari,

    The problem with the mandatory calorie listing is that everybody mistakenly assumes you can measure calories exactly. You cannot. A given fast-food hamburger calorie count will vary. Not every patty (in the package) is identical. Some will have a little more fat, others less. Some will be a little bigger, some smaller. And not every set of toppings is the same. The difference between mustard and mayo, for example, is large.

    What I mean is that there will be a variation in the stated numbers. How much? Who knows? I know—that is, I know the answer to “Who knows?” Nobody.

    Meal Combo #1 lists out at 600 calories, and people expect 600. But it might be 700 or it might be 520. What is needed in a “plus or minus” range, chosen so that we are, say, 90% sure the actual calorie is in the range. Something like 600 +/- 80.

    But once you put up the range, lawyers will think the high end of it is the most accurate; dieters will go with the low.

    Meanwhile, everybody already knows—and this is the point—that constantly and consistently eating fast food is bad for you. The calories count is superfluous information and is ripe for gaming (using the ways I suggested above).

  6. Matt,

    Excellent points. I suppose I knew that deep down, but I must admit that my reasons for liking the calorie listings is not that I want to keep my calories down, but that I’m usually hunting for the most calorie RICH food. Sometimes I can’t tell if it’s the chicken or the beef, so if a specific meal has more listed calories, it can be a useful guide for me to get the most “bang for my buck.” Well, not that a fast food meal is really offering much of anything but sugar and protein.

    But then again, I think that the cornerstone of not being unhealthy is to eat a balanced diet and exercise.

    Crazy thoughts, right?

  7. In approximately one third of cases of essential hypertension cases, (i.e. cases where no other obvious cause such as kidney failure are observed), reducing salt intake may be found to alleviate the symptoms.

    What this is saying is that as you get older your body has greater difficulty in adjusting the salt content of your blood.

    So the proposal is that we all, whether it benefits us or not, should cut down our salt intake and eat blander food because it might lower the BP of a few of us.

    Incidentally, the levels at which blood pressure is regarded as high have been slowly reduced over the years in much the same way that obesity has gone from ginormous to somewhat overweight.

    If you suffer from the syptoms of high blood pressure then see a doctor. If you can regulate your BP by decreasing your salt intake, then good. If your local politicians try to change your lifestyle in this way then vote the bums out.

  8. Your tounge can taste 4 things. Sour, sweet, bitter, and salty. It has evolved that way for a reason, you need salt. Regulate yourself. Nanny government go away. Are they going to keep salt off the table in the restaurant? Prohibit chefs from using salt. Couldn’t think of making your food taste as bland as could be. Chefs of NY rebell!

  9. Tracey Reiman from PETA also seems concerned about the number one cause of deaths in the US for slightly different reasons! and has written to Ben & Jerry’s to express her concerns. Thanks to the previous post by Briggs I found this link from the Harvard Law school comment on the Business Association Blog.com. They’ve really lost it if this is for real.
    http://www.wnbc.com/news/17539627/detail.html

  10. And for those of you who do suffer from high blood pressure my advice to you would be to stop watching the Crazy Eddies in Congress.

  11. Clyde writes: “the highest and best role of government is to ensure that the information is available. they can disseminate the information directly, or allow tax breaks for companies that make the information available (non-profit groups, tax deductions for R&D expenditures).”

    I take some exception to that statement. First, information and knowledge are two different things. Erroneous information is information, after all.

    Second, neither data nor analysis are free. It costs money to collect and analyze data sets and to disseminate them. So when the government acquires and promulgates “information,” somebody has to pay for that. Somebody meaning taxpayers. Speaking as a somebody, I am rather fed up with the government squandering my hard earned income.

    Here is a better idea: if a “consumer” desires “information,” let the consumer pay for it. The free market can provide that service to those who want it. Those who don’t, such as myself, can remain blissfully ignorant about what the government thinks is best for us. If the government would plug its cake hole, I would be happier and richer for that, and I suspect many other people would be, too.

  12. Salt is a great choice for discussing the claims of negative health effects of those things we consume everyday. Salt is a necessity for life (at around 500 – 1500 mg/minimum daily intake.) Less than that can be harmful, even fatal (although some do-gooder will no doubt try to ban it), and more than that can be harmful, although how much more is open to debate and individual biology.

    http://www.saltinstitute.org/27.html

    http://www.saltinstitute.org/rss/health-other/2008/07/pesky_data_keep_undermining_th.html

    Yea, I know these links are to the “evil” salt industry institute and not to pure-at-heart, unbiased government funded studies… Rant off.

  13. James LeFanu in the UK Telegraph on salt and Sid the Slug.

    http://www.telegraph.co.uk/health/main.jhtml?xml=/health/2004/10/04/hdoc03.xml

    Rich

  14. Here is a good link on the relationship of salt intake and mortality. After all, mortality is what we are acutally trying to prevent.

    http://junkfoodscience.blogspot.com/2008/06/traffic-tickets-for-salt-does-healthy.html

  15. As stated earlier, salt is a biological necessity in mammals and fish.

    Salt provides chlorine to form hydrochloric acid, enabling us to digest food. Hard to survive without food. Hydrochloric defenses are employed in the immune system too.

    Salt further provides sodium and in much lower percentages other metals (some with nutritional value). Sodium is an electrolyte that conveys electrical signals from the brain.

    Salt regulates the retention of water, in humans, and for that matter in fish.

    Salt has been enormously valuable, since before the days of refrigerators and freezers. It is used to preserve food so homo sapiens can chow down. The corns of corn beef were salt crystals.

    Simply put, salt is food for life on our planet.

    No wonder some idiot would like to ban it.

  16. Excess salt intake does not cause hypertension except in rare individuals with true sodium-dependent high blood pressure. Drastically lowering your dietary salt intake will have a minuscule effect on your blood pressure – much less than a 1% drop.

    As noted above, guidelines for labeling someone as “hypertensive” have changed dramatically over the years. Due to this “drift” in what is considered normal about 60% of the US adult population is now considered hypertensive. Interestingly, there is considerable controversy in this area as many physicians have noted that the panels of experts making these recommendations contain many members with ties to the pharmaceutical industry – so take it with a grain of you-know-what.

    If you live long enough, you have a 90% chance of developing hypertension and if you live longer a 100% chance of dying.
    Low salt intake is MUCH more pathologic than high salt intake.

    I’m not sure what the highest and best role of government is but to my mind it has nothing at all to do with my decisions on what to eat. Apparently for New York City “Health Czar” Thomas Frieden the highest and best role of government is to increase the size and scope of his fiefdom and consequently of course his power and budget.

  17. R RobinsonMD’s comment that “Excess salt intake does not cause hypertension except in rare individuals with true sodium-dependent high blood pressure” makes me wonder if the claimed link between salt and hypertension is an instance of generalising from an atypical subpopulation to the general population without demonstrating that the link really applies to the latter. This apparently happens far more often than one would like, especially in the case of complications related to diabetes (see http://junkfoodscience.blogspot.com for examples of this).

    Thanks also for pointing out the drift due to reclassification. This is also seen in the fear-mongering about obesity and is yet another example of the scurrilous practice of turning normal variations into pathological conditions for the profit of snake-oil merchants and authoritarians.

  18. Surely everyone knows that the leading cause of death is breathing? Surveys have shown that close to 100% of people who die were breathing shortly before.

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