Randomized controlled trials - The what, when, how and why.

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.