Ah yes, research. I think Pinker is referring to violence over the last millennia and is not focused on periods of time between US administrations. If Obama was hiding behind the semantics of his comments and really meant to say it in that way, then I'm not surprised. But as a President, he should be cognizant of the fact that anyone listening to that comment is going to view it as a statement of rating himself against other administrations (which would be a resounding laugh if we were to be asked to believe such a farce).