Table 3. Methodological quality score using the CASP scale of relevant studies. CASP scale Brown et al (2004) Brown et al (2008) Caulfield & Garrett (2004) Caulfield et al (2004) Delahunt et al (2006) De Ridder et al (2015) Doherty et al (2016) Lee et al (2017) Lin et al (2011) Suda et al (2009) Zhang et al (2012) Did the study address a clearly focused issue? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Did the authors use an appropriate method to answer their question? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Were the cases recruited in an acceptable way? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Were the controls selected in an acceptable way? Yes Yes Yes Yes Yes Yes Yes Yes No Yes No Was the exposure accurately measured to minimize bias? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes CT Aside from the experimental intervention, were the groups treated equally? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Have the authors taken account of the potential confounding factors in the design and/or in their analysis? CT CT CT CT CT CT CT CT CT CT CT How large was the treatment effect? CT CT CT CT CT CT CT CT CT CT CT How precise was the estimate of the treatment effect? CT CT CT CT CT CT CT CT CT CT CT Do you believe the results? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Can the results be applied to the local population? Yes Yes Yes Yes CT CT Yes CT Yes Yes Yes Do the results of this study fit with other available evidence? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes CT Yes score (%) * 9(75) 9(75) 9(75) 9(75) 8(67) 8(67) 9(75) 8(67) 8(67) 9(75) 6(50) Level of evidence 2 2 2 2 2 2 2 2 2 2 2 * Scores are based on items 1 thorough 12. CASP, Critical Appraisal Skills Programme; CT, cannot tell.