Year	% of total
1991	29.91457379652703
1992	26.32177214715396
1993	27.585628344724192
1994	27.741243531794737
1995	28.447118755456902
1996	29.740470039529168
1997	30.07101627066313
1998	30.4769207236312
1999	31.536779381643306
2000	31.82205219315748
2001	32.3728058714453
2002	32.31613526559972
2003	33.12601533344579
2004	33.674103399565624
2005	34.45689641235004
2006	33.662965604827264
2007	34.13539913063512
2008	34.76092843926781
2009	34.98306110280895
2010	36.67229917119003
2011	35.70213975908908
2012	34.975368356000914
2013	35.23286829512798
2014	35.09537898111532
2015	35.01597538397485
2016	35.782175681805334