Table 2.

Quality appraisal summary scores for external validity and internal validity

	Internal validity score	External validity score
Alloway (2011)	++	+
Åsberg Johnels et al. (2014)	+	+
Çelik et al. (2016)	+	+
Mano et al. (2017)	+	+
Mayes and Calhoun (2007)	+	−
Tamm et al. (2014)	++	+