Year	% of total
1990	19.299367682962405
1991	19.627334441330277
1992	17.092455196715395
1993	17.571498816206645
1994	18.007194647014042
1995	19.288530404129023
1996	19.651659057556
1997	19.866263924142977
1998	21.27015143888967
1999	22.115793163242834
2000	21.479652459417903
2001	22.39961736688165
2002	23.15354776690276
2003	24.6258923856555
2004	25.765027838282233
2005	25.077528138075515
2006	26.45844319612788
2007	25.360545800940656
2008	25.16620433913611
2009	25.629799564007683
2010	26.334312626934835
2011	25.27853549844589
2012	25.757491963337984
2013	25.779701288035373
2014	26.361526103005705
2015	27.00906972193028
2016	27.339659770822184