Wednesday, April 27, 2011

Global Burden of Disease: Epidemiologists at Work.

Cancer Cell #14

Angela Canada Hopkins, American Contemporary, Artist's collection, undated.

At the end of the century recently passed, the 20th century, huge strides were made by epidemiologists in understanding the distribution of disease and the effect of disease on not only economics but also upon human well being and culture. I have been thinking a great deal about risk lately, and herein I propose to discuss the origins of a tool developed in epidemiology to assess risk, specifically the conception of the DALY, which is an acronym for Disability Adjusted Lost Years. In case anyone thinks that "lost years" refers to some time that one spent the first years of college smoking pot and going through all sorts of machinations in hopes of getting into someone's pants - even going so far as to incur the risk of driving to Greenpeace "No Nukes" rallies with the object of one's desire - "lost years" here refers to what is also known as "YLL" or "YoLL," - Years of Lost Life. On the simplest level, "years of lost life" might be nothing more than not living to "average life expectancy" because one has incurred a risk of, say, of getting cancer through exposure to gasoline, or dying of a pulmonary embolism as the result of particulates lodged in one's lungs, though in practice, calculations of this type are way more sophisticated than that.

The important fact is that the unit developed is designed to quantify risk.

First I need to be clear about something: I am not an epidemiologist, but - in the spirit of being unafraid to approach any topic with the intention of learning more about it - and because my professionall work is peripherally involved in epidemiological conceptions - I often speak with epidemiologists in connection with my work - I thought it might be worthwhile to review what I have taught myself about their tools.

The main references for this diary will be a series of four publications published in the early 1990's by the epidemiologist C.J.L. Murray who was then Executive Director of the Evidence and Information Cluster at the World Health Organization......beginning with the less than succintly titled Quantifying the burden of disease: the technical basis for disability-adjusted life years. (Bulletin of the World Health Organization, 1994, 72 (3): 429-445). Dr. Murray, who is a physician and an epidemiologist, is now an Adjunct Professor of Population and Public Health at the Harvard School of Public Health.

Despite the fact that his titles (for himself and his papers) are as long winded (if more meaningful) than NNadir diaries, Dr. Murray's works are widely cited in the primary scientific literature.So what is the "DALY" and what is meant by the "Global Burden of Disease" beyond the obvious dimension of disease burdens?

I'll let Murray speak for himself on these points:

Why measure the burden of disease?

The intended use of an indicator of the burden of disease is critical to its design. At least four objectives are important.

- to aid in setting health service (both curative and
preventive) priorities;

- to aid in setting health research priorities;

- to aid in identifying disadvantaged groups and
targeting of health interventions;

- to provide a comparable measure of output for
intervention, programme and sector evaluation
and planning.

Not everyone appreciates the ethical dimension of health status indicators (4). Nevertheless, the first two objectives listed for measuring the burden of disease could influence the allocation of resources among individuals, clearly establishing an ethical dimension to the construction of an indicator of the burden of disease.

The bold in the word ethical is mine.

Without a doubt, an attempt to quantify ethics is immediately on shaky ground. How for instance can one rectify say, Ayn Rand type "ethics" - which I think that most of here regard as something of a very, very, very, very bad (and profoundly unfunny) joke - with the ethics of a Eleanor Roosevelt or a Raul Wallenberg? Still, the exercise may be a worthy one.

Many statistical measurements, such as the Gini index - which measures the distribution of weath in a culture and can be used to measure things like the distribution of decent health care in a culture - do have quantifiable aspects that should evoke an ethical response. It is possible to quantify distributions of access to health care by measurements of those portions of a population that have, for example, access to vaccination, or regular check ups, or laboratory blood work. A Gini type calculation might - I'm not aware of such research but am merely suggesting a possibility - measure the number of persons who can afford to have their cholesterol level checked - and compare two or three cultures. Obviously such a distribution would be very different if determined in French culture than if were determined in American culture or Malian culture. (If - as we may expect - nearly every person in France can have his, her or its cholesterol checked, their Gini distribution would be lower than in the United States, where some large percentage of the population has no access to health care, and even worse (at least we hope as Americans) in Mali, where access to laboratory tests are only available to the elite.

(For the record, most of nations that measure worse in the economic Gini wealth distribution index are not considered "first world" countries), although China, nominally socialist, has recently entered first world status while having a slightly worse Gini coefficient.)

Obviously in an increasingly complex world, ethical responses should have at least some basis in measurable data.

Also - and this is the point I think that Dr. Murray and his co-workers at the World Health Organization surely intended to make - it is definitely in a world of limited resources necessary to choose effective responses that will give the greatest and broadest benefit for the resources expended.

It would be unwise for instance to invest hundreds of billions of dollars to distribute home cholesterol test kits in France, since little change to health status would be effected and we might ethically argue that such money, if available, would produce a better result in building laboratories in Mali. However, without any knowledge of the data connected with the Malian health care system, such a determination would be impossible.

However, a very real and very urgent ethical point - very, very, very slippery in fact - would be in comparing the relative worth of a Malian with a French person, particularly if one is either French or Malian.

The Global Burden of Disease study conducted in the 1980's and 1990's was an effort to begin with the obvious point of determining what, actually, are the main causes of death in the world, and then, what the main causes of premature death. Surprisingly until that time - much of what was known on the that subject came largely on an ad hoc and lest than comprehensive and systematic basis.

The risks of ignorance of these things is, in fact, enormous. To quote Murray's paper again:

More importantly, there may be no open discussion or debate on key value choices or differential weightings. The wide variation in the implied value of saving a life in public safety legislation is but one example (8). Alternatively, we can explicitly choose a set of relative values for different health outcomes and construct a single indicator of health. The black box of the decision-maker's relative values is then opened for public scrutiny and influence.

Now, let me step back for a second and state my personal view that "public scrutiny" is usually an exercise in unbridled stupidity - with such stupidity being whipped up by the undue influence of very, very, very, very badly educated and narrow minded "journalists" possessing ersatz ethics.

For instance - and this is is diary about nuclear energy just as my recent diary about suspicions that talc in cosmetics causes ovarian cancer was also (albeit not explicitly) about nuclear energy - the "public" is supposed to have decided that nuclear energy is more "dangerous" than air pollution. Because of the mindless rote visceral unethical uneducated anti-nukes there is no open discussion of whether it is more important that 21 people at Fukushima are known to have been exposed to more than 100 microseiverts of radiation - with none having died from radiation more than a month into the accident and none likely to die from radiation in the near future - than the epidemiologically well known fact that more than 5000 people die each day from air pollution.

The fact that people on this website will invest thousands upon thousands upon thousands of hours debating the issue of whether someone, even 1000 or 10,000 people may face increased risk of getting, say cancer, has nothing at all to do with the far greater and far better understood risks of climate change - and the attendant rise in sea levels making any tsunami anywhere at any time even more devastating, with or without the agency of a nuclear facility being involved.

If - and this won't happen by the way - 10,000 people died from "eventual" cancers shown to be by a possible Bayesian analysis to be attributable to Fukushima, it still would not be the equivalent of two days worth of deaths from the normal operational output of dangerous fossil fuel plants, never mind the well known carcinogenic effects of say, crude oil, now distributed essentially forever, over the floor of the Gulf of Mexico.

For the record, the National Institute of Environmental Health and Safety, is conducting a study, The GuLF study on the health effects of populations and workers - many hundreds of thousands if not millions - of people exposed to carcinogenic crude oil exposure from the Horizon oil spill.

Where are the brainless Greenpeace types calling for banning oil?

I'll tell you where, driving their cars around to "No Nukes" meetings because of a 14 meter tsunami struck a nuclear plant in someone else's country. In brainless driving around (an using up nuclear and non-nuclear electricity to post insipid web posts) the Greenpeacees are effect making an argument that any life lost to nuclear causality is infinitely (and the word "infinite" still applies since immediate radiation deaths are still zero) to millions of energy related deaths from other causes, included but not limited to air pollution.

(No tsunami or earthquake was involved, by the way, in the explosion of the Horizon oil platform disaster off the coast of the United States and the Horizon oil platform explosion immediately incinerated more people than have died thus far from Fukushima.)


The fact is that a 14 meter tsuami swept over a nuclear facility, and stored nuclear fuel from its operations over decades and - compared objectively with the loss of life from non-nuclear causes connected with the same event, the tsunami - resulted in trivial loss of life. I don't know about you, but the feeling that anti-nukes are disappointed that the nuclear death toll was not enormous is palable from where I sit.

Anyway, about DALY's:

As I pointed out earlier in this diary, DALY's cannot help but be involved with some type of value judgment, and in fact a consideration of the mathematical distribution function that expressed one type of value judgement implicit in the DALY - the weighting of a person's age at the time of attributable death (say for instance from ozone exposure) - drew me to these seminal papers on the subject.

However, to be fair, again, it goes without saying that my reconsideration of DALY's, with which I was generally familiar, and my need to having a deeper understanding of their basis, was generated by my moral and intellectual disgust at the (to me) obvious international expressions of ignorance and superstition that have surrounded Fukushima.

Murray refers to, but divorces himself from quasi-philosophical approaches to value judgements with respect to the DALY.
This paper is not intended to present a new paradigm for measuring health, nor to firmly identify one intellectual tradition such as utilitarianism, human rights, or Rawls' theory of justice (9) as the basis for the social preferences incorporated into DALYs. Rather, the majority of the paper is devoted to a discussion of several types of social preferences which must be incorporated into any indicator of health status. In order to derive a usable indicator, a particular stand is also taken on each of the social values described. The philosophical basis for this position will not be argued in detail.

Thus, perhaps breezily, sweeping these points away, Murray describes the basic assumptions, with which, frankly I personally have no problem whatsoever. They are, with direct citation of the text:

(1) To the extent possible, any health outcome that represents a loss of welfare should be included in an indicator of health status.

Suppose one is studying coal miners on a Native American Reservation, like say, miners at the Kayenta coal mine, the official position of the management at this website notwithstanding that the only Native Americans ever injured by energy mining related causes were uranium miners. Murray argues that one need not wait for a Kayenta coal miner to die before accounting for the effect of coal on the health of the Dine people. If miners are disabled by say, black lung, and cannot work, the DALY should be designed to include the effects of this loss of productivity. Similarly, if a worker at Fukushima whose dose of radiation exceeded, say, 250 microsieverts, develops leukemia 15 years from now, the effect on his or her productivity is incurred not at death, but at the moment of disability.

I can live, and perhaps die with that.


(2) The characteristics of the individual affected by a health outcome that should be considered in calculating the associated burden of disease should be restricted to age and sex.

Murray makes reference to the belief on the part of some scholars that some people are, in fact, worth more than others, and that therefore demographic factors like education level, and individual importance to the economy makes a difference. By the logic of these scholars, individuals who have earned, say, a Ph.D. at Harvard, like, say, Kurt Wise are "worth" more than say, the guys and gals who clean Boston's sewers, because "society" has invested more in Kurt Wise than in the guys and gals in the sewers. Of course, the fact that Kurt Wise is actually a waste of humanity - as is a person who claims that by having earned a Ph.D (in something) and then joining Greenpeace one has proved Greenpeace a worthy organization - is generally not included in a value judgement which weighs a person of high educational status more than one who lacks an education entirely. One could make similar types of arguments: About 25 or 30 - I've lost count - people right now depend directly on my job performance for their economic well being.

Murray rejects all such distinctions.

If I die tonight from an embolism however, the lives of those people who feel they "need" me to help them hold their jobs need not be permanently effected; management may merely replace me with another executive, maybe with someone better at the job than I am. If there is a surfeit of people who can do what I can do, society doesn't really lose, and if there is a shortage of people who can do what I do, there is loss to society, but overall, over the range of all possible deaths from embolisms, things average out. Few, if any individual human beings have any profound level of importance in measuring the burden of disease.

In the DALY, only age and sex count, and the reasons for this should be obvious: If an old fat fart like me dies from Fukushima or ozone or exposure to crude oil or gasoline, it is not the equivalent of my sixteen year old son dying from any of these things. But other things like Kurt Wise and the sewer guys average out.

Thus I am the equivalent of a male greeter at Walmart who happens to be the same age as I am where my life or death are represented in a DALY calculation. Similarly if the guys who know how Boston's sewers work die on the job, the impact on society as a whole may actually be greater than if Kurt Wise dies.

(3) Treating like health outcomes as like

We articulate a principle of treating like health outcomes as like. For example, the premature death of a 40-year-old woman should contribute equally to estimates of the global burden of disease irrespective of whether she lives in the slums of Bogota or a wealthy suburb of Boston. Treating like events equally also ensures comparability of the burden of disease across different communities and in the same community over a period of time. Community specific characteristics such as local levels of mortality should not change the assumptions incorporated into the indicator design. The value of a person's health status is his or her own and does not depend on his or her neighbour's health status.

'Nuff said.

(4) Time is the unit of measure for the burden of disease

These are the "YoLL" type units mentioned in the intro of this diary. One attempts to understand how long a person should or could live and then by comparing factors in the lives of certain subsets of people, people who have had tuberculosis for instance, or AIDS or who have cancer, determining how many years of expected or achievable life have been lost as a result of these diseases. It follows almost immediately that such a calculation can easily be extended to giving insight to risks incurred by people to use just one example who have worked to clean up leaks of carcinogenic crude oil on the beaches of exclusive Florida white sand Gulf beaches in time for the tourist season for example - to see whether crude oil leaks have a quantifiable effect on health.

Of course, one can never been comprehensive. It may be possible to determine by examing things like "causes of hospital admissions" or "visits to physicians" or "death certificates" to determine cancer rates in a population, including maybe, most, if not all, of the population of the entire world. However it is more difficult to assertain whether any or many of said people who appear as cancer victims have worked with carcinogenic oil. It is certainly not possible to review the health records of the many hundreds of thousands (or millions) of people who were exposed - and are still be exposed - to Deepwater Horizon oil. Nevertheless one may draw statistical inferences, and by statistical means - connected largely with the size of samples - make fairly precise, with the likelihood that one is making an accurate association as measured by what are called "confidence limits" - estimate of the risk of crude oil exposure, or gasoline exposure.

Still it is important to be careful about what the takeaway from such statistics. The State of Florida has defined "screening" levels for Deepwater Horizon carcinogens, found in it's coastal waters and in beach sediments. It is useful to review the document and see that the "screening levels" are risk weighted, specifically, the components of dangerous crude oil in the waters off Florida are considered a risk to human health if they raise the lifetime risk of getting cancer by 1 X 10-6, or one in a million. This means that among one million people exposed to such levels there will be one additional cancer at these levels. Of course, during the disaster in the Gulf, exposure vastly exceeded these "safe" levels by vast amounts. Nevertheless such things are somewhat fuzzy because for many compounds in dangerous crude oil, their actual carcinogenicity is poorly understood, and, of course, people in the Gulf are often exposed to a host of other carcinogenic agents. But, be all that as it may, increased risk is often confused in the minds of the general public with certainty.

The comedian George Burns lived to be 100 years old despite the fact that during his 90 year show biz career he famously (for at least 80 years of performance) appeared while smoking a cigar. Now, a medical doctor in whose care he may have been in his 60's would have certainly advised him that he was at risk of getting cancer from his habit, but he didn't get cancer. He died as the result of complications from a fall.

One may look at George Burns and interpret these results as an indication that smoking cigars is safe but the problem has to do with sample size.

Of the four great Nobel Laureate American scientists who did the much to found the American commercial nuclear industry, three of the four, Seaborg, Wigner, and Bethe lived more than 87 years: Bethe died at the age of 99, just one year short of the lifetime of George Burns, Wigner - considered to be not only a scientific genius but also an engineering genius - lived to be 93, and Seaborg, who not only worked with some of the most radioactive elements known, and in fact was discoverer or co-discoverer of 10 of them, died at the age of 88, from a stroke. One of the American (although he won the Nobel while still a citizen of Italy) scientists, Enrico Fermi - who built the world's first nuclear reactor (in a squash court in Chicago) - died at the age of 53 from stomach cancer.

One cannot, of course, draw the conclusion that Fermi's death proves that people who work on nuclear reactors will die before 60, nor can one prove from Bethe's case that people who work on nuclear reactors will come close to becoming centigenarians.

The sample size of Nobel Laureates who worked on the development of nuclear energy is simply too small. (Alvin Weinberg, who was mentored by Wigner, and who considered Wigner to be his intellectual father, who was also the designer of the Pressurized Water Reactor which dominates the world's commercial nuclear fleet, and the in many ways superior Molten Salt Reactor - a reactor in a permanent and deliberate state of "meltdown: - which has never been commercialized, much to the loss of humanity as a whole - lived to be 91. One of Weinberg's ideas that has thus far proved a failure was his promotion of the National Renewable Energy Laboratory. Thus far the entire failed Renewable Energy - it's toxicological implications ignored by an insipid and unaware public - has done nothing more than to function as a fig leaf for the gas industry.)

At Fukushima, 21 people seem to have been exposed to more than 100 microsieverts of radiation, most within a period of a few weeks, some with a period of a few hours. None of them have died thus far from radiation (or anything else), but all of them will die, although not necessarily from radiation related effects. It may be that all of them will die of cancer, in which case dumb people will take it as "proof" that "nuclear energy is dangerous," although, again, 11 people were incinerated instantly when the Deepwater Horizon rig blew up in the Gulf producing zero calls from the mental midgets at Greenpeace for the immediate phase out of oil. On the other hand, none of the 21 Fukushima 100+ μSv exposed persons may get cancer, in which case this will not be proof that such exposures are safe.

For sure these people will be intensely studied, and their medical records will be elaborate. But because the sample size is so small, any conclusions drawn will be essentially meaningless.

Right now of course, the inane and toxic Greenpeace crowd will sit around on their useless consumer cult asses, claiming - or at least implying strongly - that every cancer in Japan henceforth can be attributable to Fukushima, even though before Fukushima, among humanity as a whole, everyone has roughly a 1 in 5 chance of dying from cancer. NOT ONE of the anti-science, anti-intellectual, dogmatic assholes in this toxic organization will stop for a second to consider the possibility that if cancer rates in Japan do rise in the area of the tsunami that it could be the result not only from the reactors but also because of carcinogenic gasoline leaking from tens of thousands of smashed cars or, for that matter, highly carcinogenic solvents leaching from smashed semiconductor plants, including those where solar cells for the failed (and toxic) solar industry are manufactured.

As it happens, right now, Japan has the highest life expectancy in the world. This should not be construed as evidence that having two cities destroyed by nuclear weapons is good for public health. The sample size of countries in which one (or more) cities have been destroyed by nuclear weapons is too small, one.

This limit to the sample size of nations that have been victims of nuclear war has been observed for more than 60 years, despite many representations by less than honest (and decidedly dogmatic) people like the (Snowmass) Valley Girl Amory Lovins that nuclear power will inevitably lead to nuclear war. (World production of nuclear energy has increased 4 fold since the insufferable ass Lovins wrote an insufferably stupid paper making this claim in 1980, when he was commenting on the supposed "death of nuclear power.")

But this brings me to my final point about the structure of the statistical "risk" measure, the DALY.

Japan's population is aging and birth rates in that country are actually below the replacement rate. This means that the mean and median ages of citizens in Japan is rising.

One of the factors included in the DALY is a "discount rate" for human beings. The rationale for this approach is that as humans age, society invests in them - in the form, first, of health care, then education - which may last two or three decades - and finally professional training. After this "investment" according to the theory, people reach a maximum "return on the investment" with their productivity increasing and their "contribution to society" being accrued. By this scheme, losing a man or woman at the age of 30 costs society more if society has invested substantial resources in them - in terms of education and training - since society has not generally accrued all of the possible benefits of the productivity derived from said education and training.

By contrast - this will sound cold - children under 10 represent very little "investment" by society in most cases, and society can stand the loss of children better. Similarly, after the age of 65 (62 if you're lucky enough to be French), people have retired and, in fact, they are often simply consumers rather than producers. (Before anyone attacks me for this let me say that many elderly people do produce significant and important work. Hans Bethe, mentioned earlier, worked on very important areas of physics right up to his death.

Murray uses what he calls a "modified Delphi method" - consultation with a panel of "experts" - this may be the most unsatisfactory part of the paper because (for my taste) it's way too touchy-feeley to choose the constant β in the continuous function he proposes for age weighting from a "seat of the pants" geometric consideration:
f(x) = Cxe-βx

The oracles at Delphi consider that the optimal value of β that can be chosen is 0.04, which gives a function with a maxima at around 30 years of age.

The need for a continuous function avoids large discrete calculations - given that this approach is nearly 20 years old - which, back then at least, would have been very demanding for computers of the time. This may be less true today.

The complete description of the DALY function for individual calculations of the DALY - the solution for a differential equation - is given in the paper. It is too cumbersome to attempt to produce it in this editor.

In any case, Japan has one of the most elderly populations in the world, with about 25% of its citizens being over the age of 65. Part of this may be explained by long life expectancy in this country, which produces about 30% of its electricity from nuclear energy.

Given the age weighted nature of the DALY, appeals to this measure of risk in connection to the events of Fukushima will be influenced and one should keep this in mind if one is interested in metrics.

However, if one is not concerned about measurement, may I suggest huge outbursts of hysteria, fear, wild suppositions, inattention to trivial things like control groups, and of course that old standby, hearing only what one wants to hear.

Anyway, I should close.

If you are unlucky enough to be struck by a tsunami while driving your safe car around, try not to think how much more fun the tsunami would be if sea levels were jacked up another meter. What's important is that the world's largest source of climate change gas free primary energy be risk free, and if it's not risk free, we should abandon it for other things, accepting any degree of risk, because the perfect should always be the enemy of the excellent.

Have a nice coal, oil and gas powered day tomorrow.

(Orignally posted at Daily Kos with an amusing poll.
Here is the link.)

1 comment:

Jim Van Zandt said...

With beta=.04 yr^-1, the suggested age weighting function has a maximum at exactly 25 yr.


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