Year	% of total
1990	17.144909872529123
1991	17.781363405659544
1992	18.084778113639928
1993	18.725020094674953
1994	18.941061527051048
1995	19.01782340001883
1996	19.501315344349297
1997	19.743389215698624
1998	19.346678136696784
1999	19.638937614967464
2000	19.987304559859755
2001	20.95022910125843
2002	20.859891702021542
2003	21.329804093619675
2004	21.887341077293588
2005	22.038403661937235
2006	23.055822100036565
2007	22.855407133172175
2008	23.159235781940655