I heard this on NPR recently: “Why we can't find what we're looking for”. Researchers at Harvard Medical School are studying how good people are at finding rare occurring problems, people like airport security personnel and radiologists looking for tumors.
“We know that if you don't find it often, you often don't find it,” said [Lead researcher Jeremy Wolfe].
In the NPR interview, the researcher went on to say even when doing the experiment on himself, with full knowledge of how many pictures in the stack of 2000 contain images with guns in them, he can't make his own accuracy increase. And any urgency brought to bear on the worker knowing what's at stake if something is missed does not seem to have any impact on their performance.
Rare stuff often gets missed. That means that if we look for 20 guns in a stack of 40 bags, we'll find more of them than if we look for the same 20 guns in a stack of 2,000 bags.
I think this has interesting implications for developers trying to find bugs in their code. Sheer willpower is not enough to improve our quality.
Another NPR story from Feb 11 2013 updates the prior one -- “Why Even Radiologists Can Miss A Gorilla Hiding In Plain Sight” -- covers this topic.
When you ask someone to perform a challenging task, without realizing it, their attention narrows and blocks out other things. So, often, they literally can't see even a huge, hairy gorilla that appears directly in front of them.
That effect is called “inattentional blindness.”
He took a picture of a man in a gorilla suit shaking his fist, and he superimposed that image on a series of slides that radiologists typically look at when they're searching for cancer. He then asked a bunch of radiologists to review the slides of lungs for cancerous nodules. He wanted to see if they would notice a gorilla the size of a matchbook glaring angrily at them from inside the slide.
But they didn't: 83 percent of the radiologists missed it, Drew says.
see also DarkIsTheDefault, TestCheckList, WhyUnitTest