[Interpretation of negative clinical trials]. / La interpretación de los ensayos clínicos negativos.

Randomized clinical trials without statistically significant differences between treatment groups may provide useful information for clinicians. However, negative trials must be interpreted cautiously, since the absence of evidence of treatment effect is not the same as evidence of absence of treatment effect. Before the reader of a negative article can conclude that one intervention was not better than the other, the potential causes of a negative study should be explored. The objective of this manuscript is to critically describe some of the most common methodological problems that can explain the lack of difference between studied groups in randomized clinical trials.