ON March 6, Terry and Jon Poling stood outside a federal courthouse in Atlanta, Ga., with their 9-year-old daughter Hannah and announced that the federal government had admitted that vaccines had contributed to her autism. The news was shocking. Health officials at the Centers for Disease Control and Prevention and at the American Academy of Pediatrics have steadfastly assured the public that vaccines do not cause autism. Now, in a special vaccine claims court, the federal government appeared to have said exactly the opposite. What happened? The answer is wrapped up in the nature of the unusual court where the...