Table 2. Study quality risk bias assessment for randomized clinical trials.

Study ID	Adequate Randomization	Allocation concealment	Blinding	Baseline characteristics Balanced	Lost to follow up (<20%)	Incomplete data (attrition bias)
Comerota 1996 (STILE II)	Yes	Yes	No	Yes	Yes	No
Groar 1994 (STILE)	Yes	Yes	No	Yes	Yes	No
Nillson 1991	Yes	Yes	No	Yes	Yes	No
Ouriel 1996 (TOPAS)	Yes	Yes	No	Yes	Yes	No
Ouriel 1998	Yes	Yes	No	Yes	Yes	No