The Left Hand of Obama

Voters in the 2008 Presidential election didn't have a meaningful choice. Whichever box they ticked, they were voting for a lefty.

Yes, Obama and McCain are both sinistral, a rather unlikely occurrence since just 7-10% of adults are left handed. Netherlands-based neuroscientists Casasanto and Jasmin decided to make use of this coincidence to test the hypothesis that people tend to make "good" gestures with their dominant hand and "bad" ones with their off-hand, in a new PLoS paper: Good and Bad in the Hands of Politicians.

They analyzed the final televised debates from the '04 and '08 elections, in which the candidates discussed various topics, both positive i.e. their own policies, and negative i.e. their opponent's Vietnam War records, choice of running-mate, and association with dodgy preachers. They also examined the gestures that the speakers made to accompany their positive or negative points, and recorded which hand they used. George W. Bush and John Kerry are both right-handed, by the way.

Here's what they found:
Both lefty candidates tended to use their left hands for good gestures and their right hands for bad ones, while the right-handed showed the opposite pattern. The data also reveal some interesting facts about the overall number of gestures: Obama had a hands-off approach with only 119 gestures in total, while McCain was gesticulating all over the shop (259). Bush and Kerry, however, were essentially equal (192 vs 193). Maybe Kerry's one extra gesture was just one too many for the electorate, thus costing him the Presidency.

Anyway, does this prove that we use our dominant hands to make "good" gestures - supporting the notion that we unconsciously associate positive ideas with our dominant side of space, and negative ideas with our non-dominant side? Well, this study includes a large amount of data: it is, statistically, very likely that Obama really does tend to use his left hand over his right hand for positive gestures, i.e. this is unlikely to be due to random chance.

But does this mean that there's a correlation between handedness and good-gesture-lateralization? We actually only have 4 data points relevant to that question: Obama, McCain, Kerry and Bush. We have a lot of information on each of those people, but there are only 4 independent sets of data.

Suppose that everyone has a hand-they-use-for-good-gestures, and that it's 50/50 whether it's left or right - that is to say, suppose it has nothing to do with your general handedness. Clearly, there's then a 50% chance that any given person's good-gesture-hand will match their handedness, just by coincidence. There's a 1 in 4 chance that, for any two people, both will have a match; it's 1 in 8 for three people and 1 in 16 for four people. Which implies that there's a 1 in 16 chance that these results would have happened purely by chance.

Maybe we need to look back to the Clinton / Dole debates to get some more data...

Daniel Casasanto and Kyle Jasmin1 (2010). Good and Bad in the Hands of Politicians: Spontaneous Gestures during Positive and Negative Speech PLoS ONE