Consistent- versus Inconsistent-Handed Predicts Better than Right- versus Left-Handed

At Berkeley, Andrew Gelman and I taught a freshman seminar about left-handedness. Half the students were left-handed. We did two fascinating studies with them that found that left-handers tend to have left-handed friends. I kick myself for not publishing those results, which I bring up in conversation again and again.

After the class ended I got a call from a journalist who was writing an article about ridiculous classes. I told him the left-handedness class had value as a way of introducing methodological issues but all I cared about was that his article be accurate. He decided not to include our class in his examples.

Stephen Christman, who got his Ph.D. from Berkeley (and did quirky interesting stuff even as a graduate student), and two colleagues have now published a paper that is a considerable step forward in the understanding of handedness. They argue that what really matters is not direction of handedness but the consistency of it. The terms left-handed and right-handed hide a confounding. Right-handers almost all have very consistent handedness (they do everything with the right hand). In contrast, left-handers much more often have inconsistent handedness: they do some things with the left hand, some with the right. I am a good example. I write with my right hand, bat and throw left-handed, play tennis left-handed, ping-pong right-handed. In fact, I am right-wristed and left-armed. When something involves wrist movement (writing, ping-pong) I use my right hand. When something involves arm movement (batting, throwing a ball, tennis), I use my left hand. Right-handers are much more similar to each other than left-handers.

Christman and his co-authors point to two things: 1. When you can get enough subjects to unconfound the two variables, it turns out that consistency of handedness is what makes the difference. Consistent left-handers resemble consistent right-handers.  2. Consistency of handedness predicts many things. Inconsistent-handers are less authoritarian than consistent-handers. They show more of a placebo effect. They have better memory for paragraphs. And on and on — about 20 differences. It isn’t easy to say what all these differences have in common but maybe inconsistent-handers are more flexible in their beliefs. (Which would explain the friendship findings in our handedness class.)

I think about these differences as another example of how every economy needs diversity and our brains have been shaped to provide it, one idea underlying my theory of human evolution. Presidents of the United States are left-handed much more than the general population. For example, Obama is left-handed. The difference between Presidents and everyone else is overwhelming and must mean something. Yet left-handers die younger. I would say that in any group of people you need a certain fraction, not necessarily large, to be open-minded and realistic. That describes inconsistent-handers (who are usually left-handed). These people make good leaders because they will respond to changing conditions. People who are not open-minded make good followers. Just as important as realism is cooperation, ability to work together toward a common goal.


9 Replies to “Consistent- versus Inconsistent-Handed Predicts Better than Right- versus Left-Handed”

  1. My mother told me that I was left-handed as a tiny child and seemed to have swapped to right-handedness by copying the rest of the family. Does that happen or was my mother mistaken? A counterargument is that falling in with people around me is not one of my most conspicuous traits. A supporting argument is that as a soccer player I was noticeably more “two footed” than most of my teammates – so much so that I was usually played on the left.

    Seth: maybe there is also “inflexible handed” and “flexible handed”. You are flexible handed. Your story about changing the hand you write with suggests testing everyone to see how good they are at writing with the less-usual hand (e.g., right handers write with their left hand). That would be good research. Would not depend on self-report (e.g., “which foot do you prefer to kick with?”).

  2. Left-handers die younger? Then why didn’t my life insurance company ask me if I was left-handed?

    Seriously, I thought this was urban legend that was debunked long ago (people once claimed a 7 year difference in life expectancy, which is crazy). But maybe there’s new information I don’t know about?

    Seth: I looked around for new evidence about the longevity difference. I couldn’t find any. As far as I could tell, several studies support the idea that left-handers die younger, and a few studies do not, in the sense of no significant difference (either way). Absence of a significant effect is weak evidence.

  3. This is very interesting. I’ve always had trouble specifying which is my dominant hand.

    I do things such as writing and brushing my teeth with my left hand, but when I was learning to play golf, left-handed clubs didn’t work out. I also use my right hand for tennis and ping pong.

    Saying that I’m inconsistently handed seems much more accurate.

  4. My handedness is exactly the same as Seth has described. I think of it as being lefty for forehand actions and righty for backhand ones, but the wrist-arm breakdown may be closer to the mark.

    I’m not that good a leader, though.

  5. Very interesting. Like some of the earlier posters I’ve never known how to properly specify which hand is dominant. I write with my right, play golf, lacrosse and bat with my left, snowboard goofy (typical for lefties), play ping pong right, etc. Never occurred to me that there might be a difference in handedness between arm and wrist as Seth writes. I’m also clearly right eye dominant which may play into things.

  6. I am right-handed except for two handed sports. In cricket I bowl right-handed, & bat left-handed I shoot & play golf left-handed. This is because my left eye is my master eye.

  7. As an inconsistent-hander, I have always snickered at those detective stories that include a scene in which a left-handed potential suspect is ruled out because some crime was obviously committed by a right-hander. I wonder how much this particular misconception has affected real police work.

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