Year	% of total
1990	17.71949142394721
1991	18.06118824898864
1992	18.159881849037802
1993	18.657139235668097
1994	18.758952604258457
1995	19.447402811055078
1996	19.64694302291038
1997	19.450069560125538
1998	19.575241845151353
1999	20.43081664239253
2000	20.832388780783972
2001	20.517582449217837
2002	21.21841275367525
2003	21.17296162637722
2004	21.070508425881084
2005	21.263515884548955
2006	21.532229994887757
2007	22.130994988431567
2008	22.934891848679325
2009	23.784088922722535
2010	24.13888702467505
2011	24.554665065230466
2012	25.417938714024565
2013	25.703050288339195
2014	25.793838798724043
2015	26.134524905495027
2016	27.092822428512655