Commentary to 'short-term outcome of mild isolated antenatal hydronephrosis conservatively managed'.
A major limitation of this observational study is the lack of a comparison group during the study period. A small comparative study prior to the one they are describing does not qualify. Observational studies provide weaker empirical evidence than do experimental studies because of the potential for large confounding biases. Theother limitation is their sample size. Based on the incidence of UTI on and off prophylaxisprovidedby theauthors (8%and13%), thenumber of children required in each arm would be over 900 (alpha 0.05 and power 0.8). The value of this cohort study is to provide preliminary evidence that can be used as a basis for designing a stronger experimental study, such as a randomized controlled study, to answer the question they posed.