"NATURAL" EXPERIMENTS
 

    Sometimes, it's possible to lay an experimental template over actual events and undertake analyses as though we had designed some grand experiment to be conducted in real life.  Following the Three-Mile Island nuclear accident in 1978, researchers set about constructing, in retrospect, an experimental design in which they would have selected comparable nuclear power plants and then caused an accident in one of them, as a way of determining the consequences of such an event.