The integrity of science requires, among many other things, avoiding the misleading use of statistics and data. Yet one of the easiest and most common ways to misrepresent science or to mislead the public and policy makers is to selectively choose data that tells only part of a story, or the wrong part of a story.
A common way to do this is through the use of a misleading comparison, or what I call the inappropriate denominator trick. Here are three examples from recent interactions between policy and science, from three very different fields, where science and statistics are being misused in a similar manner to mislead the public and policy makers.
Bottled water and groundwater use: Many local communities with existing or proposed bottled water plants are concerned that so much water will be pumped from local aquifers that local streams, ecosystems, or wells used by farmers or homes will be badly affected. I discuss examples in detail in my new book: Bottled and Sold: The Story Behind Our Obsession with Bottled Water. The bottled water industry, however, regularly tries to mislead the public by comparing their use of water to an irrelevant, but very large number, i.e., by using a misleading denominator. For example, a paper from the industry-funded Drinking Water Research Foundation (self-described as "Co-located with and partially supported by the International Bottled Water Association in Alexandria, VA") concluded "Total annual bottled water production in 2001 was found to be a trivial component (0.019%) of total fresh groundwater withdrawals." In this case, the industry is dividing their water use (the numerator) by a huge number (total national groundwater withdrawal) intentionally chosen to make their impact appear small. This misleading comparison will be small consolation in the local communities where the actual consequences of inappropriate groundwater withdrawals are felt.
The BP oil spill in the Gulf of Mexico: The CEO of BP, Tony Hayword, recently used the exact same misleading denominator trick when he said:
"The Gulf of Mexico is a very big ocean. The amount of volume of oil and dispersant we are putting into it is tiny in relation to the total water volume."Wow. Nervy. This will be of small consolation to the coastal communities, the fisheries, the dead and dying wildlife, and the economy of the Gulf Coast, for whom the spill is a very big deal, no matter how large the volume of the Gulf of Mexico. This is also a grossly misleading comparison driven by an inappropriate denominator.
Carbon dioxide and climate change: The third example, in exactly the same misleading vein, is the claim by some that carbon dioxide is such a tiny fraction of the atmosphere (over 390 parts of CO2 in every million parts of the atmosphere - the inappropriate denominator comparison again), that human production of CO2 couldn't possibly be affecting the climate. This grossly misleading (and grossly scientifically incorrect) claim is like saying we can add just a little bit of cyanide to a glass of water and not worry about it - after all, it's just a tiny bit compared to the volume of water in the glass. Wrong. In this case, the misleading statistic is only part of the problem; the argument is faulty science too. It is, of course, the effectiveness of each molecule in trapping energy that counts, not only the number of molecules. And the role of carbon dioxide and other gases that also contribute to the earth's greenhouse effect is incredibly well understood by scientists.
Scientists and the public must call out such phony science and point out misleading uses of statistics, by all sides. These kinds of misleading comparisons, whether done intentionally by polluters or anti-environmental extremists or environmental activists on the other side, or unintentionally by people who just don't know better, should be highlighted and disputed quickly and publicly, so that policy makers are not misled.
The bottom line? Some bottled-water company groundwater extractions can and do cause local problems. The amount of oil pouring into the Gulf of Mexico is causing vast environmental and economic damage. And human additions to greenhouse gases are changing the climate.
Peter Gleick, Pacific Institute