Fact – (No Source) = Factoid.

In an article about pollution in China, the New Republic dropped in this eye-popping statement: “Sixteen of the 20 dirtiest cities in the world are in China.” No source, but hey, the New Republic is just a popular journal.

To find the cities listed, I went for the source. What follows is my search free of any reference to dates, though the New Republic piece did just come out.

“Voice of America” told me, “The Worldwatch Institute in Washington says 16 of the world's 20 most polluted cities are in China.” And sure enough, at Worldwatch’s site, I found the statement, “Globally, China is home to 16 of the 20 cities with the most polluted air.” But Worldwatch offered no source or study, even though a “China Watch” features prominently at its website. Since Lester Brown’s outfit is a press-friendly operation focused on getting media attention for environmental issues, I wasn’t totally surprised they offered up the eye-catching “16 of 20” sentence with no source to back it. Maybe they simply read it somewhere else?

In TIME for example? TIME oddly had the same statement as Worldwatch, but attributed it not to Worldwatch but to the World Bank, saying, “the World Bank has reported that 16 of the 20 most polluted cities in the world are Chinese.”

OK, now the World Bank's a credible source, a UN heavyweight that puts out lots of hard facts. So I went to the Bank. And in their “China Quick Facts,” sure enough appeared this similar, but slightly different, sentence, “And China has 20 of the world's 30 most polluted cities, largely due to high coal use and motorization.”

Where did that sentence come from? I searched the World Bank site. No study. No source. Just other writings using the same “fact”. Is the World Bank just another part of an echo chamber passing around the same undocumented factoid?

I don’t know. Maybe such a study exists. But I have my doubts, especially after finding Scientific American had published a study done by the Blacksmith Institute that lists the world’s 10 most polluted cities. Topping the list: Sumqayit in Azerbaijan. The top Chinese city, Linfen in Shanxi [pictured], ranks 6th, and Tianying in Anhui is 9th. Four other Chinese cities are in Blacksmith’s “Dirty Thirty”, making Chinese cities 6 of 30. Not good, but not 10 of 30 like the former USSR’s most polluted, and certainly not 20 of 30 or 16 of 20.

Whom can you trust?