Scratching beneath 'The Scratching Case': systematic reviews and meta-analyses, the back door for evidence-based medicine.

Endometrial scratching or injury was first suggested a decade ago as a simple intervention to improve endometrial receptivity in patients undergoing ART. More than a decade later, based on weak evidence some doctors have adopted this strategy, although there is not yet agreement about its real benefit. In this opinion paper, we analyze the methodological and plausibility problem beneath 'the Scratching Case'. This is also applicable to several other examples of spurious associations reported in the literature. In particular, we emphasize what should be done so as not to dilute evidence-based medicine by a vicious circle created by the over-exploitation of inadequate or insufficient data to compute incorrect or incomplete conclusions.