Unilateral Biportal Endoscopic Discectomy versus Microendoscopic Discectomy for the Treatment of Lumbar Spinal Stenosis: A Systematic Review and Meta-Analysis

Table 3

Risk of bias of cohort studies.

Study	Selection				Comparability of cohorts	Outcomes			Score
	Representativeness of cohort	Selection of nonexposed cohort	Ascertainment of exposure	Outcome lacking at the beginning		Outcome assessment	Sufficient follow-up time	Follow up adequacy
Heo [24]	+	+	+	+	++	—	+	+	8
Choi [22]	+	+	+	+	++	+	+	+	9
Heo [23]	+	+	+	+	+	+	+	+	8
McGrath [28]	+	+	+	+	+	+	+	+	8
Rieger [31]	+	+	+	+	++	+	+	+	9
Kim [27]	+	+	+	+	+	—	+	+	7
Ito [25]	+	+	+	+	++	+	+	+	9

, The total score of NOS evaluation is 9 points; +, represents that the item has obtained the score; -, represents that the item has not been scored.