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The first Republican president once said, "While the people retain their virtue and their vigilance, no administration by any extreme of wickedness or folly can seriously injure the government in the short space of four years." If Mr. Lincoln could see what's happened in these last three-and-a-half years, he might hedge a little on that statement.
-Ronald Reagan

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Wednesday, June 12, 2002
Lies, Damn Lies, and Conservative Statistics

Instapundit today posts an item quoting from an article in Reason attacking Rachel Carson for misuse of statistics in her Famous book, "Silent Spring".

Carson was also an effective popularizer of the idea that children were especially vulnerable to the carcinogenic effects of synthetic chemicals. "The situation with respect to children is even more deeply disturbing," she wrote. "A quarter century ago, cancer in children was considered a medical rarity. Today, more American school children die of cancer than from any other disease [her emphasis]." In support of this claim, Carson reported that "twelve per cent of all deaths in children between the ages of one and fourteen are caused by cancer."

Although it sounds alarming, Carson’s statistic is essentially meaningless unless it’s given some context, which she failed to supply. It turns out that the percentage of children dying of cancer was rising because other causes of death, such as infectious diseases, were drastically declining.

In fact, cancer rates in children have not increased, as they would have if Carson had been right that children were especially susceptible to the alleged health effects of modern chemicals. Just one rough comparison illustrates this point: In 1938 cancer killed 939 children under 14 years old out of a U.S. population of 130 million. In 1998, according to the National Cancer Institute, about 1,700 children died of cancer, out of a population of more than 280 million. In 1999 the NCI noted that "over the past 20 years, there has been relatively little change in the incidence of children diagnosed with all forms of cancer; from 13 cases per 100,000 children in 1974 to 13.2 per 100,000 children in 1995."

Of course, these aren't those squishy, soft-headed, statistics that relativistic, Luddite, anti-Enlightenment liberal environmentalists love to terrify the innocent with. A good conservative/libertarian writer would never resort to such tricks, especially after just attacking an environmentalist for them. These are firm, trustworthy, conservative statistics with rock-hard pecs and abs, ready to stand up to the toughest challenge.

Aren't they?

The 81% increase in child fatalities looks unimpressive compared to the 115% increase in population. But the first problem is exactly that the comparison is to total population. We know that the percentage of the population in older brackets has increased dramatically in this period. Logic dictates that the percentage of younger groups in the population, including children, would have gone down. In the 1940 census, 36.3% of the population was under 21; in 2000 28.6% was under 20. So by comparing rates in children against total population instead of comparing against population of children, Baily is distorting the numbers by about 20%.

But this isn't the real trick. The real problem is that Bailey is comparing cancer fatalities and ignoring the dramatic improvements in treatments over the comparison period. From 1960 to the late 1980s, chances for 5 year survival of a child diagnosed with cancer went up dramatically , from 28% to 70%. For the period from 1938 to 1998, the difference would be even higher. So if cancer fatalities have stayed fairly constant for that period, it follows that cancer incidence must have risen dramatically.

According to this NCI report, from 1975 to 1995 mortality rates for children dropped 40% while incidence rates were rising at 0.8% per year. Incidentally, this report defines 'children' as birth - 19. If Bailey's report does the same, that's one more problem in comparing it to a report on children aged birth - 13. Bailey has just thrown out some numbers to make it look impressive - as long as you don't look too closely.

The bottom line is that you just can't make any meaningful statements about environmental risks for cancer by comparing mortality rates over generations. Any environmental factor more subtle than smoking 4 packs of unfiltered cigarettes a day while working in an asbestos mine will be drowned out by the treatment improvements.