Year	% of total
1990	19.31549214932099
1991	19.594250625430206
1992	19.769978927448843
1993	20.447876535376338
1994	20.537723590047648
1995	20.812440128180093
1996	21.047205399833725
1997	20.87550981057459
1998	20.912712556186946
1999	21.704047647989416
2000	22.163641502877674
2001	21.671668840002454
2002	22.483075708099765
2003	22.50343841391795
2004	22.581491868971398
2005	22.7573200406905
2006	23.065860520944227
2007	23.589956653328194
2008	24.578099080419793
2009	25.390850627706786
2010	25.907717339504998
2011	26.53433590304644
2012	27.523942516164844
2013	27.651205216446265
2014	27.96944851728563
2015	28.7580547649073
2016	29.868612159780966