“…Eight studies obtained a score below 75% on the Quality Assessment Scales (Deveau & Leitch, 2015; Farragher, 2002; Green-Hennessy & Hennessy, 2015; Helin, 2007; Hidalgo, Maravić, Milet, & Beck, 2016; Huefner, Griffith, Smith, Vollmer, & Leslie, 2014; Jani, Knight, & Jani, 2011; Nunno, Holden, & Leidy, 2003) and were excluded, while seven received a perfect score. Although almost all of the included studies presented specific and adequately described objectives or research questions, 9 of the 19 quantitative or mixed studies did not control for confounding variables (see Table 2).…”