2.6. Risk of Bias in the Individual Studies

Two independent researchers assessed methodological quality of the studies using the PEDro scale; there was a third researcher to settle cases of doubt or disagreement. The PEDro scale [26] evaluated 11 items, scoring each item as 1 or 0, depending on whether the item fulfilled study criteria or not, respectively. External validity was assessed using Item 1, internal validity using Items 2 through 9, and interpretability of the results using Items 10 and 11. The first item was not taken into account for the final score, which could be a maximum of 10 points. Each article was classified according to the score obtained: “high quality” if its score was ≥6, “moderate quality” with a score of 4-5, and “low quality” if the score was <4.

Also, the RoB2 tool was performed. It is the second version of the Cochrane tool to assess the risk of bias in clinical trials. The biases are evaluated in 5 domains: (1) randomization process, (2) effect of being assigned to intervention, (3) missing outcome data, (4) measurement of the outcome, and (5) reported results. Within each domain, 1 or more questions must be answered. These answers lead to the judgements of “low risk of bias,” “some concerns,” or “high risk of bias” [27].