From State to Nation: What Makes a Policy Spread?

Ever wondered how a law starts in one state and then spreads across the entire country? In the U. S. , many national policies begin as state laws. But why do some state laws become national while others don't? Researchers have looked at where a law starts, what type it is, and even the wealth or political leanings of the state that passes it first. They wanted to see if these factors could predict whether a state law would become a national policy. To find out, they built models to forecast if a state policy would go national and how many states needed to pass it first. Surprisingly, they found that the state's characteristics didn't matter much. What really counted was how many states adopted the policy. For example, same-sex marriage and laws about methamphetamine precursors spread differently. The models helped predict when these policies might become national. The researchers also made a data-driven guess about when marijuana legalization and "stand your ground" laws might go national.