Lies, Damned Lies & Statistics

Dissecting and debunking a popular damage claim

Mullein (Verbascum thapsus), as observed at Grey Owl Gardens in Paonia, Colorado, 2023.

Another excerpt from the book-in-progress I am co-authoring with Nikki Hill, “Don’t Blame the Messengers: A critique of the ‘invasive plant’ narrative.”

Our concern is harm to ecology, not economic loss, especially since economic interests are largely responsible for the harm we oppose. But we must address one oft-cited economic claim: that “invasive species” cost the US an estimated $138 billion annually.

Numbers, just for being numbers, lend a validity to arguments, both in the sciences and in popular culture. Attaching a figure to one’s point makes it sound more authoritative, whether it’s deserved or not. Culturally, numbers are associated with tangible things like clocks, rulers, speedometers and our own ability to count. Statistics, though, inhabit a more abstract space, as we will discuss below. But the impression made by a number like $138 billion is real, and even more real is the subsequent action that is justified, like spraying herbicides willy-nilly, or mowing down a patch of vegetation despite the fact that wildlife are utilizing it for food and shelter.

The source of the $138 billion figure is “Environmental and Economic Costs of Nonindigenous Species in the United States,” a 2001 paper by David Pimentel, et al.ⁱ How “oft-cited” is it? Over 2200 instances by other papers as of January 2024, and innumerable times by popular media, anti-“invasive” agencies and environmental groups. Most of the mentions outside scientific literature are not attributed to the paper and just state the estimate as if it’s well established, or even as a fact. Pop “$138 billion” and “invasive species” into a search engine and you’ll get back hundreds and hundreds of results.

Given the paper’s wide acceptance and dissemination, you might assume its data and methodologies are rock solid. You would be wrong. When subjected to scrutiny, much of it is revealed as unsupported, exaggerated, or just plain sketchy.