Risk of bias in individual studies
The methodological quality of the included studies and the possibility
of bias were assessed using the modified Newcastle–Ottawa, Pierson and
Bradford Hill scales for case and case series reports21. The authors of this scale recommend assessing the
quality of the studies according to four categories, selection,
ascertainment, causality and reporting, with eight specific questions to
answer giving low (1–3 questions), medium (4–6 questions) and high
(7–8 questions) quality values. This analysis was carried out
independently by each of the two investigators, and in cases of
disagreement, the third acted as a mediator.
This study was sent to the Ethics Committee of Clinical Research of
Galicia (Spain), stating that ethical approval was not required for this
type of study. Written consent of the patient was obtained.