| Ratings Author(s) | A. Selction bias | B. Study design | C. confounders | D. Blinding | E. Data collection method | F. Withdrawals and dropouts | Rating |
| Aiken et al. (2014) | strong | strong | Strong | moderate | strong | weak | Moderate |
| Aiken et al. (2002) | Strong | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Aiken et al. (2001) | Moderate | Weak | Weak | Moderate | Weak | Strong | Weak |
| Al-Kandari & Thomas (2008) | Strong | Weak | Moderate | Moderate | Strong | Moderate | Moderate |
| Amaravadi et al. (2000) | Strong | Strong | Strong | Moderate | Strong | Weak | Moderate |
| Ball et al. (2013) | Moderate | Weak | Strong | Moderate | strong | Moderate | Moderate |
| Carthon et al. (2012) | Moderate | Weak | Strong | Moderate | Moderate | Moderate | Moderate |
| Cho et al. (2003) | Moderate | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Cho et al. (2015) | Strong | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Cho & Yun (2008) | Moderate | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Cimotti et al. (2006) | Moderate | Moderate | Strong | Moderate | Strong | Strong | Strong |
| Cordova et al. (2014) | Moderate | Moderate | Moderate | Moderate | Strong | Weak | Moderate |
| Daud-Gallotti et al. (2012) | Moderate | Moderate | Moderate | Strong | Moderate | Moderate | Strong |
| Duffield et al. (2011) | Moderate | Weak | Moderate | Moderate | Strong | Moderate | Moderate |
| Glance et al. (2012) | Strong | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Halm et al. (2005) | Weak | Weak | Moderate | Moderate | Strong | Moderate | Weak |
| Hayes & Ball (2012) | Weak | Weak | Weak | Moderate | Weak | Weak | Weak |
| Hugonnet et al. (2007) | Moderate | Moderate | Weak | Moderate | Strong | Moderate | Moderate |
| Hinno et al. (2011) | Weak | Weak | Strong | Moderate | Strong | Moderate | Weak |
| Holden et al. (2009) | Moderate | Weak | Strong | Moderate | Strong | Strong | Moderate |
| Jones (2014) | Weak | Weak | Strong | Moderate | Strong | Weak | Weak |
| Kiekkas et al. (2008) | Moderate | Weak | Strong | Moderate | Strong | Strong | Moderate |
| Kovner et al. (2002) | Moderate | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Liang et al. (2011) | Moderate | Moderate | Strong | Moderate | Strong | Moderate | Strong |
| Needleman et al. (2002) | Moderate | Moderate | Strong | Moderate | Strong | Moderate | Strong |
| Pearson et al. (2004) | Moderate | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Potter et al. (2003) | Moderate | Weak | Moderate | Moderate | Strong | Moderate | Moderate |
| Rogowski et al. (2013) | Moderate | Moderate | Strong | Moderate | Strong | Moderate | Strong |
| Sasicbay-Akkadecbanunt et al. (2003) | Moderate | Weak | Strong | Moderate | Strong | Moderate | Moderate |
| Screuders et al. (2015) | Moderate | Weak | Moderate | Moderate | Strong | Moderate | Moderate |