Table 2.

Methodological quality of prospective case–control research based on the NOS.

Included studies	Study population selection	Comparability	Exposure or results	Levels
Basile et al. (2021) (22)	☆☆	☆☆	☆☆☆	7☆
Quartuccio et al. (2015) (24)	☆☆	☆	☆☆☆	6☆
Roccatello et al. (2016) (25)	☆☆☆☆	☆☆	☆☆☆	9☆
Saadoun et al. (2008) (10)	☆☆☆	☆☆	☆☆☆	8☆
Saadoun et al. (2010) (11)	☆☆	☆☆	☆☆☆	7☆
Zaja et al. (2003) (29)	☆☆☆	☆☆	☆☆☆	8☆
Terrier et al. (2012) (30)	☆☆☆	☆☆	☆☆	7☆

Stars are used to denote scores. ☆corresponds to one point, ☆☆correspond to two points, ☆☆☆correspond to three points, ☆☆☆☆correspond to four points.