Methods: To compare the clinical effectiveness of these two treatment options, the investigators will conduct three separate retrospective comparative effectiveness studies for each of these diseases using detailed electronic data on diagnoses, procedures, laboratory tests, and orders for drugs and devices supplemented by limited chart review from 43 free standing children's hospitals that are members of the Children's Hospital Association (CHA) (study years 2009-2011, total sample size will exceed 15,000 children). The primary outcome will be rehospitalization for treatment failure. The investigators will use conventional and propensity-score based methods, including matching, to estimate and compare the effect of the two treatment options on patient outcomes. These comparisons will have the goal of asking about the effect of therapy as if the patients had been randomized to one of the two treatment options.