The pattern seems clear: A mass shooting is followed by loud calls to tighten America's gun laws, yet there is no change before the next massacre.
That is not exactly accurate, however. Change often does happen — but toward looser gun laws, according to an examination of the past three decades of violence.
A recent working paper by three researchers at Harvard Business School attempted to analyze how states respond to shootings at the policy level. The researchers tallied mass shootings across the U.S. since 1989 and looked at state gun laws that were introduced and passed over the same period.