Table 1. Quality appraisal of observational studies using the Newcastle-Ottawa tool.

Study	Representative of Exposed Cohort	Non-Exposed Cohort	Assessment of Exposure	Outcome of interest not present at the start of the study	Comparability	Assessment	Follow up	Adequacy of f/u	Total
O'Sullivan et al. [1]	1	0	1	1	1	1	1		6
Sultan et al. [12]	1	1	1	1			1		5
Alushi et al. [15]	1	1	1	1	1	1	1		7
Sinning et al. [16]	1	1	1	1	1	1			6
Masri et al. [17]	1	1	1	1	1	1	1	1	8
Schewel et al. [18]	1	1	1	1	1	1	1		7
Barbash et al. [21]	1	1	1	1	1	1	1		7
Testa et al. [24]	1	1	1	1	1	1	1		7
Nijenhuis et al. [25]	1	1	1	1	1		1	1	7
Kleczynski et al. [26]	1	1	1		1		1		5
Keymel et al. [27]	1	1	1	1	1	1	1		7
Mujeeb et al. [28]	1	1	1	1	1				5