Comparison of the efficacy and safety of the chronological groups (1997–2003 versus 2006 to 2009 and 2012 to 2014) regarding the microsurgical procedure.

Chi-Square tests examine the 0-Hypothesis H0 that there is no difference regarding the rate of clipped cases (n = 246) in the comprehensive group of 1997–2003 (n = 361) compared to the rate of clipped cases (n = 144) in the comprehensive recent microsurgical clipping group (n = 281) (microsurgical 2006–2009 and 2012–2014). Moreover Fisher-exact tests and Chi-Square tests examine the 0-Hypothesis H0 that there is no difference regarding the rates of symptomatic ischemic stroke, occlusion rate, rebleeding, direct mortality and reinterventions between the two chronological groups (“Microsurgical 1997–2003” versus “Microsurgical 2006–2009 and 2012–2014”).