Study	Reason for exclusion
Coats 1980	The allocation was quasi random and prone to cause selection bias. It is described in the article as, ”women who were admitted to the delivery suite were randomly allocated into two groups by the last digit of their hospital numbers“. In addition, when the staff performed an incision which was inappropriate to the treatment allocation, the woman was removed from the trial.” This withdrawal of women as opposed to the principle of’ intention-to-treat analysis’ increases the risk of selection bias
Detlefsen 1980	This study does not compare the restrictive use of episiotomy versus the routine use of episiotomy
Dong 2004	This study does not compare the restrictive use of episiotomy versus the routine use of episiotomy
Henriksen 1992	The allocation was quasi random. As explained in the article, “the deliveries were assisted by midwives on duty when they arrived on the labour ward”. This method of allocation is very prone to selection bias
Werner 1991	There is no reference about the method of randomization used. The effects are not shown in a quantitative format making the data uninterpretable