Year	% of total
1990	31.355854058898547
1991	30.6989115979148
1992	31.18238205627915
1993	27.40402837708681
1994	26.452815350645515
1995	28.580550621310497
1996	28.704661484251076
1997	30.543271258502397
1998	28.95910499345315
1999	27.5055323372729
2000	29.098650717182526
2001	26.88644238977011
2002	25.546063802378818
2003	27.57306638291852
2004	28.1774822353463
2005	24.71882790622817
2006	28.73859863110539
2007	29.237693671841267
2008	29.07277229174936
2009	32.57199505949597
2010	32.094639686505275
2011	36.00037766777365
2012	32.79123446827065
2013	33.49774310581329
2014	36.29001506857193
2015	36.09295206142128
2016	37.154914571272585