But she was right, no matter which flavor you prefer. Math can be hard. Sometimes people get it all wrong, either accidentally or intentionally. Here’s an example of each.
I was listening to the Diane Rehm show today, and the topic was high-speed rail in the US. One caller with great intentions but not a lot of math skills wanted the US to move all freight on trains instead of having any transported by trucks. “That would lower the number of traffic deaths infinitely!” Umm, no. It might lower truck-caused traffic deaths by 100% (although I doubt it – the train will not deliver to Walmart), but it surely cannot lower it by 101%. Yes, there are occasional births on highways, but these are not caused by trucks. Creating a life takes longer than ending a life. So the caller was enthusiastic and well-intentioned, but wrong.
I’m more suspicious about the second example of bad math. The California Milk Advisory board has been showing a series of advertisements, with real California dairy farmers, to promote the fact that their milk is good. The tag line is that 99% of California dairy farms are family owned. I don’t doubt the percentage, but I suspect that it is hiding some more information. Let’s get all hypothetical. There are exactly 100 dairy farms in California, and 99 of them are family-owned. Let’s further suppose that each family-owned farm has one cow. And suppose that the single commercial enterprise has ten thousand cows. It is still true to say that 99% of the farms are family owned, but it’s also true that 99% of the milk comes from the non-family farm. And while I haven’t been able to confirm the idea behind my conjecture, I found a comment saying that 40% of the milk production comes from farms that are not family owned. That is unsubstantiated, so it’s hearsay. The California Department of Food and Agriculture does put out a publication (link to 2009 report on this page – I’m not going to link to a 9M PDF file directly!) showing the count of cows per farm, broken down by county. Page 11 shows that Kern county has an average of over three thousand cows, on each of its over 50 farms.
There are six counties that have over a thousand cows per farm, and indeed the California average is over a thousand cows on each of its 1752 farms. Three thousand cows is not exactly a mom and pop operation, even though that’s what the commercials want you to believe.
The next time you hear some numbers tossed around, think about them a bit before you accept them and their implications.