Year	% of total
1970	31.32808504411459
1971	30.858501227716058
1972	31.43385622110934
1973	32.58135712595376
1974	33.86087674097983
1975	35.183994999529716
1976	36.8962703720059
1977	38.31273987431637
1978	39.336460331010244
1979	40.49006456039566
1980	41.61199064226805
1981	42.801951922278214
1982	44.017730010268416
1983	45.180371221765306
1984	46.520402778364286
1985	47.846402204367614
1986	48.96812778384951
1987	49.91010824726065
1988	50.85743022265671
1989	50.786057328351475
1990	68.21232458816353
1991	68.05555555555556
1992	69.99325691166554
1993	69.88795518207283
1994	69.6376811594203
1995	68.44444444444444
1996	69.48324022346368
1997	70.15121630506246
1998	70.77114427860697
1999	71.42857142857143
2000	72.04724409448819
2001	73.125
2002	74.22178988326849
2003	75.09107468123861
2004	75.98627787307034
2005	76.77340899878395
2006	80.09320905459387
2007	82.621001981319
2008	84.4242125984252