How looking only at policy diffusion "successes" between states may be misleading

Ideas often have a way of spreading. This is certainly true in the case of American states; innovative policies are often adopted by others in a process known as policy diffusion. But in trying to determine which policies spread, could we be giving too much of a focus on those that are successful? In new research which examines interstate compacts, Andrew Karch, Sean C. Nicholson-Crotty, Neal D. Woods, and Ann O’M. Bowman find that an emphasis on successful policies may be leading scholars to overestimate the importance of some factors, such as neighboring state activity, and underestimate the importance of others, like the number of previous adopters.