Randomized controlled trials (RCTs) are at the top of the pyramid of evidence as they offer the best answer on the efficacy of a new treatment. RCTs are true experiments in which participants are randomly allocated to receive a certain intervention (experimental group) or a different intervention (comparison group), or no treatment at all (control or placebo group). Randomization, along with other methodological features such as blinding and allocation concealment, safeguard against biases. This review will focus on parallel group RCT design as it is the most common design in the field of Pediatric Urology. RCTs can be designed using a superiority, equivalency, or non-inferiority hypothesis, and are usually preceded by a pilot, where the trial protocol is implemented in a small number of patients, mimicking the larger, definitive study. Even though regarded as the best available option to bring out scientific data, RCTs might be prone to mislead. If RCTs are small and underpowered, a difference of even one single event between groups, may completely change the trial results. To safeguard against RCTs weakness, a fragility concept of statistical significance was developed and called the Fragility Index (FI). RCTs may not be appropriate, ethical, or feasible for all surgical interventions. They may have limitations such as prohibitive cost and unrealistic large sample sizes. Nearly 60 % of surgical research questions cannot be answered by RCTs. Therefore, clinical practice should be based on the best available evidence on a given topic, regardless of the study design. However, even in these situations, conclusions drawn from observational studies must be interpreted with caution.

Background and objectives: Posterior urethral valve is the most common cause of bladder outlet obstruction in infants. We aimed to describe the rate and timing of kidney-related and survival outcomes for children diagnosed with posterior urethral valves in United States children’s hospitals using the Pediatric Health Information System database. Design, setting, participants, & measurements: This retrospective cohort study included children hospitalized between January 1, 1992 and December 31, 2006, who were in their first year of life, had a diagnosis of congenital urethral stenosis, and underwent endoscopic valve ablation or urinary drainage intervention, or died. Records were searched up to December 31, 2018 for kidney-related mortality, placement of a dialysis catheter, and kidney transplantation. Cox regression analysis was used to identify risk factors, and Kaplan–Meier survival analysis used to determine time-to-event probability. Subgroup survival analysis was performed with outcomes stratified by the strongest identified risk factor. Results: Included were 685 children hospitalized at a median age of 7 (interquartile range, 1–37) days. Thirty four children (5%) died, over half during their initial hospitalization. Pulmonary hypoplasia was the strongest risk factor for death (hazard ratio, 7.5; 95% confidence interval [95% CI], 3.3 to 17.0). Ten-year survival probability was 94%. Fifty-nine children (9%) underwent one or more dialysis catheter placements. Children with kidney dysplasia had over four-fold risk of dialysis catheter placement (hazard ratio, 4.6; 95% CI, 2.6 to 8.1). Thirty-six (7%) children underwent kidney transplant at a median age of 3 (interquartile range, 2–8) years. Kidney dysplasia had a nine-fold higher risk of kidney transplant (hazard ratio, 9.5; 95% CI, 4.1 to 22.2). Conclusions: Patients in this multicenter cohort with posterior urethral valves had a 5% risk of death, and were most likely to die during their initial hospitalization. Risk of death was higher with a diagnosis of pulmonary hypoplasia. Kidney dysplasia was associated with a higher risk of need for dialysis/transplant. Podcast: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_10_03_CJN04350419.mp3