Year	% of total
1990	18.270588232157404
1991	18.630946946776096
1992	19.676586230296667
1993	20.248150934441988
1994	20.31762243648001
1995	20.93916893124755
1996	21.33253682437185
1997	20.93103251071121
1998	20.8750422984072
1999	21.81145346593754
2000	22.04953643998868
2001	21.616787234367298
2002	22.214190727056437
2003	22.198838873406732
2004	22.135050528981655
2005	22.323069651923817
2006	22.38956809379772
2007	23.041698908902628
2008	23.906354802504612
2009	24.575159806272264
2010	25.179967976567998
2011	25.371211505955152
2012	26.255527463643336
2013	26.358039193833207
2014	26.406071817127142
2015	26.74862742967162
2016	27.83251034799693