Year	% of total
1970	20.291325287234816
1971	19.820582960426925
1972	19.71663720705081
1973	19.57132981399074
1974	18.974226664302027
1975	21.06841134552882
1976	21.0320651152016
1977	21.71829842989304
1978	21.923461059209632
1979	22.147883288141696
1980	20.330466756334374
1981	22.15520871802714
1982	23.024432604053978
1983	24.628975802704037
1984	25.369089149811835
1985	26.36584623028555
1986	27.131938661032716
1987	27.076990933701534
1988	26.55047528881797
1989	27.188193462332457
1990	20.62937062937063
1991	20.43010752688172
1992	22.83464566929134
1993	21.653543307086615
1994	21.2
1995	21.428571428571427
1996	20.866141732283463
1997	21.825396825396826
1998	21.6
1999	21.75732217573222
2000	21.074380165289256
2001	19.4331983805668
2002	20.967741935483872
2003	21.428571428571427
2004	21.951219512195124
2005	21.90082644628099
2006	22.268907563025213
2007	22.64957264957265
2008	22.943722943722943