The science of the coronavirus pandemic is complicated. So is the math.

What quickly became apparent from the project was the complexity of reporting. Different states used different definitions for testing or for deaths. Data was delayed or only sporadic. Piecing together the national picture was fairly easy, but state-level evaluation was trickier. Dive one level lower to counties, and things quickly get even wobblier. It was still possible to make comparisons, certainly, but that meant dealing with a lot of exceptions to any rule. Trying to, for example, figure out the typical pattern from detecting a case to hospitalization to death yielded different results from a state to the next one over.