Year	% of total
1990	34.89802806121724
1991	34.797941297231475
1992	34.36477673645765
1993	33.51964292273266
1994	31.197010487222048
1995	30.55665001019035
1996	31.388320725307793
1997	31.264950948208714
1998	30.681234658612645
1999	31.936174983540926
2000	32.620546286466876
2001	33.281613608469
2002	33.88591769214794
2003	34.801688039499155
2004	35.377049742455135
2005	35.94196281656246
2006	35.63697565499084
2007	37.25418800126135
2008	37.07018807349186
2009	36.60193017376312
2010	37.604386680669485
2011	37.38539569883563
2012	37.61030560993896
2013	37.77710246218089
2014	38.87083952257611
2015	37.570712631018324