Year	% of total
1990	21.45459989125792
1991	22.548795108062688
1992	22.704546262905772
1993	22.924290750429538
1994	23.08568755029316
1995	23.59686256836139
1996	22.861568917091027
1997	21.960616663010622
1998	21.359365128245067
1999	22.335162660402375
2000	22.652286091123635
2001	21.484240975535965
2002	22.772641826544262
2003	22.1194916599789
2004	21.463671183131453
2005	21.371816606974036
2006	21.51198757807339
2007	22.59211379835461
2008	23.256671438496365
2009	24.78146100659617
2010	24.553615513173124
2011	26.143050479783557
2012	28.295338937001315
2013	28.17469003100633
2014	29.00283133850598
2015	30.389284539175506
2016	31.549800941602935