Beware of This Brain Glitch When Using Data

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Next time your computer spits out an error message, take a moment to thank it. At least your computer knows when a glitch has occurred. Not so with your brain. You can encounter a system error in your brain without ever knowing it.

If you’re interested, there’s plenty to read about brain glitches. A classic article by Tversky and Kahneman in Science back in 1974 does a great job of describing glitches that get us into trouble when making decisions about uncertain events. Since our brains do not send out error messages, the best we can do is to be aware of potential glitches so that we can avoid drawing the wrong conclusion and then acting on it.

Today, I’m just going to mention just one that any smallish nonprofit should know about. I think you’ll appreciate this glitch more if I can reproduce it in your brain right now. Tversky and Kahneman provide a great example that may do the trick:

“A certain town is served by two hospitals. In the larger hospital about 45 babies are born each day, and in the smaller hospital about 15 babies are born each day. As you know, about 50 percent of all babies are boys. However, the exact percentage varies from day to day. Sometimes it may be higher than 50 percent, sometimes lower. For a period of 1 year, each hospital recorded the days on which more than 60 percent of the babies born were boys.” Which hospital do you think recorded more such days: the larger hospital, the smaller hospital, or do you think they recorded about the same number of days? (Let your brain produce an answer and then scroll down.)

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If your brain said: “about the same number of days” then you’ve encountered a common glitch. We know, in the general population, about 50 percent of babies are born with the sex of male. You are more likely to see this 50/50 split in large groups (aka “samples”) than in small groups because larger groups more closely represent the entire population. Thinking about coin tosses often helps to correct glitches. If you toss a coin just 6 times, you are more likely to get a lopsided result (such as 4 heads and 2 tails) than if you toss it 60 times.

Nonprofits often deal with small groups. This can lead to errors. For example, you may go astray by:

  • Planning for what’s needed for a large program based on the experience of a small pilot program.

  • Projecting what the needs of a certain group may be over a longer period of time based on the needs of a group over a shorter period of time.

  • Applying “evidence based practices” based on studies of large groups to your smaller group of clients which may differ in key ways from the large group.

In summary, beware of small numbers when predicting and planning.

To see past data tips, click HERE.


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