Sabtu, 31 Maret 2018

In the Dark About Left-Handedness

My younger daughter is left-handed. I am teaching her how to write her numbers more legibly and being right-handed I quickly realized that this was going to be hard. So as a good academic, I asked Google to look into this and ran into an internet meme of left-handers dying earlier than right-handers. Here is the original mention in the New York Times. One of those classic "study says, blah blah blah" stories that newspapers love publishing and all of us love nodding our heads to. As usual, it is based on research, and has a truthy feel to it. 

The year is 1991, and Dr. Diane F. Halpern of California State University at San Bernardino and Dr. Stanley Coren of the University of British Columbia, publish an article in the New England Journal of Medicine. Their data show that left-handed people die when they are much younger than right-handed people. They obtained a random sample of deaths from Southern California and asked family members if the person who died was right or left-handed. In their sample, left handers died at an average age of 66 compared to 75 for right handers. They attributed it to left-handers struggling to cope in a right-handed designed world – think cars, heavy machinery etc. Buzzfeed has a funny/empathetic list (depending on your handedness) of worst things in this world for left-handed people. Check #11 which refers to the New England Journal study (left-handed people die 9 years earlier than right-handed people). 

But this finding is actually false – it is a subtle artifact of a sampling problem in the original study. The thing to realize is that in earlier times kids who were natural lefties were trained/forced to become right-handed and eventually identified by others as right-handed (remember family members answered the question, not the dead chap;) We don’t force young left-handed people to switch today. So in their sample of deaths, older folks will tend to have more right-handed people (those who are genuinely right-handed plus those who were forced to switch). Whereas amongst people who died young, a higher fraction will now be identified as left-handed. So if you divide this sample into left and right-handed people, the average age will be higher for right-handed people, by 9 years approximately. The researchers did not realize this and this led them to conclude that left-handed people die young – a horrific meme that prevails to this day. This is my attempt to reassure all left-handed people reading this. And yes, the title of the post is a play on “The Left Hand of Darkness.”