Friday, April 13, 2012

Why we look for a single cause

In a previous post, I whined about the state of econometrics, particularly the obsession with instrumental variables and single factor causes. The obvious question is why does this state of affairs persist?

"I only wish we had a single agent causing all the declines," Pettis says. "That would make our work much easier."

This is from National Geographic on colony collapse disorder.

When CCD first hit, many people, from agronomists to the public, assumed that our slathering of chemicals on agricultural fields was to blame. Indeed, says Jeff Pettis of the USDA Bee Research Laboratory, "we do find more disease in bees that have been exposed to pesticides, even at low levels." But CCD likely involves multiple stressors. Poor nutrition and chemical exposure, for instance, might pummel a bee's immunities before a virus finishes the insect off.

It's hard to tease apart factors and outcomes, Pettis says. New studies reveal that fungicides—not previously thought toxic to bees—can interfere with microbes that break down pollen in the insects' guts, affecting nutrient absorption and thus long-term health and longevity. Some findings pointed to viral and fungal pathogens working together.

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