Clinical study types and guidance for their correct post-pandemic interpretation.

Randomized clinical trials (RCTs) are key to the advancement of medicine and microbiology, but they are not the only option. Observational studies provide information on long-term efficacy and safety, are less expensive, allow the study of rare events, and obtain information more quickly than RCTs. On the other hand, they are more vulnerable to confounding factors. Prospective exploratory pilot studies share many aspects with RCTs but are not subject to supervision by external commissions or mandatory registration. Multitesting can pervert the balance of publications in favor of the desired effect. Bonferroni's reasoning shows that if 10 studies are performed with an ineffective antibiotic, the probability that at least one will show P <0.05 might be 40%. Scenarios in which there is intensive pressure to perform research, such as the recent pandemic, might result in many research teams trying to study the effect of an antimicrobial. Even if the drug has no efficacy, if 100 research teams conduct a study to assess its usefulness, it might be virtually certain that at least one will get a P value <0.05. If the other studies (with P >0.05) are not published, the scientific commu nity would consider that there is strong evidence in favor of its usefulness. In conclusion, RCTs are a very good source of clinical information, but are not the only one. The systematic registration of all research can and should be applied to all types of clinical studies.