On Tuesday we were treated to two front page stories in the Arizona Daily Star linking a health phenomenon to a supposed cause. However, such epidemiological studies prove nothing regarding cause and effect; the link or association is merely suggestive. Frequently such studies fail to consider other possible causes or confounding factors. The association between X and Y could in fact be valid, or it could be a coincidence.

The first story, written by Tony Davis, is “UA study: Diesel exhaust here linked to childhood wheezing.”

In this case, University of Arizona researchers suggest “Infants and very young children in Tucson exposed to high levels of vehicle diesel pollution are more likely than other kids to suffer from early childhood wheezing, a potential asthma indicator.” The study involved 700 children, a very small sample size for such a study, and compared the incidence of childhood wheezing with traffic patterns. According to information in the story, the researchers did not consider some confounding factors such as allergens in the study area or emissions from gasoline-powered vehicles. They did note “A majority of children have wheezing problems in the first few years of their lives due to viral infections..” But the report of the study did not say how that factor was separated from the diesel fumes association. The study report did not dig deeply into socio-economic factors that could impact pre-natal and post-natal care. The study leaves many uncertainties. And perhaps more ominously, “The researchers are also going to see if any kinds of public policies need changing to protect such children.” What would bureaucrats do; forbid families with young children from living near major traffic routes?

The second study, “Kids may help prevent heart disease in men” reported by the Associated Press involved 138,000 men. This study, by AARP, the government, and several universities noted that men with children have lower testosterone and a lower incidence of heart disease. Unlike the first story, this one was more circumspect in its claims. The story noted “a study like this can’t prove that fatherhood and mortality are related.” The story also admitted that it did not consider confounding factors such as the cholesterol and blood pressure data, fertility of the men’s partners, nor the case of being childless by choice.

These kinds of stories make good headlines but often bad science and  unwarranted worry. They can also precipitate harmful government regulation. For instance, see my post “Ozone theory has holes.”

In that story I report that the FDA is banning inexpensive over-the-counter inhalers for asthmatics and forcing them to buy more-expensive prescription medications on the theory that the CFC propellants in the cheap inhalers are harming the ozone layer. Science has proved that wrong, but the FDA apparently hasn’t gotten the message.

So, whenever you see such a story reporting a link or association of one thing to another, be skeptical, and remember this coincidence: human life expectancy has increased since the invention of the Yo-Yo. Will we someday see this headline: “Study: Yo-Yos linked to longer life”? That headline has the same validity as the stories mentioned above.

See also:

Statistical Games #1

Statistical Games #2 Stroke for Stroke

Last Friday a story in the Arizona Daily Star: “Asthmatics must switch to costlier ‘green’ inhalers” notes that asthmatics will no longer be able to purchase inexpensive inhalers because the propellant contains chlorofluorocarbons (CFCs) which the FDA thinks harm the ozone layer. The FDA said that patients who use the epinephrine inhalers (cost about $20) will need to switch by Dec. 31 to albuterol inhalers which cost $30 to $60.

Besides asthma, it seems these people will also suffer from bad science and over-zealous regulation.

Ozone (O_3, a variant of the oxygen molecule O₂) produces smog when it is at ground level, but high in the atmosphere, ozone protects us from Ultraviolet (UV) rays from the Sun.

Back in 1956, scientists noticed that the atmospheric ozone layer seasonally thinned over the South Pole. The size of the ‘hole’ varied from year to year. The reigning theory as to the cause of this ‘hole’ was that CFCs reacted with the ozone and caused its destruction leaving us vulnerable to UV radiation. This theory led to the Montreal Protocol, an international treaty promoted by the United Nations. It went into effect in 1989 and required a phase-out of all CFCs which, at the time were used mainly in refrigerators, air-conditioning units, and to a lesser extent, as propellants for inhalers.

The alleged science behind this ban, according to Wikipedia, is this:

In 1973 Chemists Frank Sherwood Rowland and Mario Molina, then at the University of California, Irvine, began studying the impacts of CFCs in the Earth’s atmosphere. They discovered that CFC molecules were stable enough to remain in the atmosphere until they got up into the middle of the stratosphere where they would finally …be broken down by ultraviolet radiation releasing a chlorine atom. Rowland and Molina then proposed that these chlorine atoms might be expected to cause the breakdown of large amounts of ozone (O₃) in the stratosphere. Their argument was based upon an analogy to contemporary work by Paul J. Crutzen and Harold Johnston, which had shown that nitric oxide (NO) could catalyze the destruction of ozone.

In other words, the catalytic reaction of CFCs on ozone was hypothesized based on “might be expected” and by “analogy.” However, there still is no proof that it actually happens in nature on a large scale.

The first chink in the CFC-ozone hypothesis came in 2007 with an article in Nature: “Chemists poke holes in ozone theory.” Chemists at NASA’s Jet Propulsion Laboratory found that the rate of photolysis (light-activated splitting) of CFCs was much slower than had been assumed. This means: “The rapid photolysis of Cl₂O₂ is a key reaction in the chemical model of ozone destruction. If the rate is substantially lower than previously thought, then it would not be possible to create enough aggressive chlorine radicals to explain the observed ozone losses at high latitudes.”

So, if it’s not CFCs, what might be causing the variation in ozone? A possible answer was presented by researcher Qing-Bin Lu (University of Waterloo, Canada) in Physical Review Letters of the American Physical Society, 19 March 2009:

This Letter reports reliable satellite data in the period of 1980–2007 covering two full 11-yr cosmic ray (CR) cycles, clearly showing the correlation between CRs and ozone depletion, especially the polar ozone loss (hole) over Antarctica. The results provide strong evidence of the physical mechanism that the CR-driven electron-induced reaction of halogenated molecules plays the dominant role in causing the ozone hole.

Independent research from Cornell, published in 2010, also found a correlation between cosmic rays and the size of the ozone ‘hole.’

The FDA’s basis for banning the inhalers is not supported by current science, so asthmatics will suffer even more from the expense to pay for an eco-fad. And really, even if CFCs do impact ozone, how much CFCs come from inhalers?

Note: The ozone is produced by UV rays breaking down oxygen. Ozone thinning normally occurs in winter when sunlight and UV rays disappear allowing the normally unstable ozone to decay. The amount and extent of decay apparently depends on cosmic ray flux.

See also:

Antarctic ozone hole may have larger role in climate change

CERN experiment confirms cosmic ray effect on climate