Selection Comparability Outcome
1 2 3 4 1 1 2 3 Total
Karoussis et al. [31] ★b ★ ★a ★ ★b ★ 6★
Gatti et al. [32] ★b ★ ★a ★ ★b ★ ★b 7★
Swierkot et al. [33]★b ★a★★b★ 5★