Year	% of total
1990	20.159499748204926
1991	20.289464339228125
1992	17.56485589510963
1993	17.999998109639478
1994	18.457400918194658
1995	19.79247509244105
1996	20.167697790669067
1997	20.39134186149205
1998	21.8015315933189
1999	22.632493744376603
2000	21.94872728452225
2001	22.872191405828183
2002	23.62877541915315
2003	25.101298824449145
2004	26.230167375320264
2005	25.523453109428193
2006	26.881416065943757
2007	25.74521803951325
2008	25.533781734251814
2009	26.145456522117737
2010	26.75110280274434
2011	25.661525521080794
2012	26.165652426535306
2013	26.14836472454096
2014	26.692112943676282
2015	27.37335216851244
2016	27.70540230444615