Sequential analysis of clinical trials allows researchers a continuous monitoring of emerging data and greater security to avoid subjecting the trial participants to a less effective therapy before the inferiority is evident, while controlling the overall error rate. Although it has been widely used since its development, sequential analysis is not problem-free. Among them main issues to be mentioned are the balance between safety and efficacy, overestimation of the effect size of interventions and conditional bias. In this review, we develop different aspects of this methodology and the impact of including early-stopped clinical trials in systematic reviews with meta-analysis.
