Fun examples of round number bias

Yesterday was a comparatively big day for round number bias.

If you are unfamiliar with this idea, Economist’s View describes round number bias as “the human tendency to pay special attention to numbers that are “round” in some way.”

First, Facebook’s Sean Taylor drew me to this article, which gave several examples of round number bias that I hadn’t hear of before. Here are my two favorites:

Baseball: at the end of the season, the share of players who hit .300 or .301 was more than double the proportion who hit .299 or .298.

SAT’s: those who take the SAT test and end up with a score just below a round number–like 990 or 1090 on what used to be a 1600-point scale–are much more likely to retake the test than those who score a round number or just above.

I’ll add two of my favorite examples to this list.

Male heights, via OkCupid: men near 6-feet tall are more likely to add a few inches to their actual heights, in order to reach the 6-foot benchmark, relative to other men. Here’s a graph – note the horizontal shift among OkCupid users who are just below 6-feet fall.

Screen Shot 2014-12-18 at 9.05.20 AM

Marathon times: USC’s Eric Allen and colleagues found that runners make extra efforts to finish just before 5-minute cutoffs, with the largest effects for the 3 and 4 hour marks. Here’s another graph, this time a histogram (link).

Screen Shot 2014-12-18 at 9.08.55 AM

It’s amazing the number of runners who finished just below 4 hours, relative to those that finished just above.


Here’s some other round number bragging that also occurred recently:

  • Greg challenged me in a race to a round number of twitter followers. So, if you aren’t yet following me on twitter, please change that.

Screen Shot 2014-12-18 at 9.13.00 AM

  • The blog you are reading recently hit 50,000 views. Thanks for checking it out!

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