A guy is driving through Texas, and passes a barn. It's got a bullseye painted on the side -- with a bullet hole in the dead center.
He sees two old-timers leaning on a fence nearby, and pulls over to talk to them.
"Did one of you guys make that bullseye shot?" he says.
One of them says, a proud smile on his face, "Yeah. That was me."
"That's some amazing shooting!"
The man says, "Yeah, I guess it was a pretty good shot."
The old-timer's friend gives a derisive snort. "Don't let him fool you, mister," he says. "He got drunk, shot a hole in the side of his own barn, and the next day painted the bullseye around the bullet hole."
This is the origin of the Texas sharpshooter fallacy, the practice of analyzing an outcome out of context and after the fact, and overemphasizing its accuracy. Kind of the bastard child of cherry-picking and confirmation bias. And I ran into a great example of the Texas sharpshooter fallacy just yesterday -- a Dutch geologist who has gone viral for allegedly predicting the devastating earthquake that hit southeastern Turkey and northwestern Syria on February 6.
The facts of the story are that on February 3, a man named Frank Hoogerbeets posted on Twitter, "Sooner or later there will be a ~M 7.5 earthquake in this region (South-Central Turkey, Jordan, Syria, Lebanon)." This, coupled with the fact that the day before, the SSGEOS (the agency for which Hoogerbeets works) had posted on its website, "Larger seismic activity may occur from 4 to 6 February, most likely up to mid or high 6 magnitude. There is a slight possibility of a larger seismic event around 4 February," has led many to conclude that they were either prescient or else have figured out a way to predict earthquakes accurately -- something that has eluded seismologists for years. The result is that Hoogerbeets's tweet has gone viral, and has had over thirty-three million views and almost forty thousand retweets.
Okay, let's look at this claim carefully.
First, if you'll look at Hoogerbeets's twitter account and the SSGEOS website, you'll see a couple of things right away. First, they specialize in linking earthquake frequency to the weather and to the positions of bodies in the Solar System, both of which are correlations most scientists find dubious at best. Second, though, is that Hoogerbeets and the SSGEOS have made tons of predictions of earthquakes that didn't pan out; in fact, the misses far outnumber the hits.
Lastly, the East Anatolian Fault, where the earthquake occurred, is one of the most active fault zones in the world; saying an earthquake would happen there "sooner or later" doesn't take a professional geologist.
What seems to have happened here is that the people who are astonished at Hoogerbeets's prediction have basically taken that one tweet and painted a bullseye around it. The problem, of course, is that this isn't how science works. You can't just take this guy's one spot-on prediction and say it's proof; in order to support a claim, you need a mass of evidence that all points to a strong correlation.
Put a different way: the plural of anecdote is not data.
No less an authority than the United States Geological Service has stated outright that despite improvements in fault monitoring and our general knowledge about how earthquakes work, quakes are still unpredictable. "Neither the USGS nor any other scientists have ever predicted a major earthquake," their website states. "We do not know how, and we do not expect to know how any time in the foreseeable future. USGS scientists can only calculate the probability that a significant earthquake will occur (shown on our hazard mapping) in a specific area within a certain number of years."
So what Hoogerbeets and the SSGEOS did was basically nothing more than an unusually shrewd guess, and I'd be willing to bet that the next "sooner or later" prediction from that source will turn out to be inaccurate at best. Unfortunate, really; having an accurate way to forecast earthquakes could save lives.
But realistically speaking, we are nowhere near able to do that -- viral tweets and spurious bullseyes notwithstanding.