Year	% of total
1970	73.61898618444914
1971	73.45841728954045
1972	72.75043410755345
1973	71.88063629080538
1974	71.35426740409933
1975	71.17247278329233
1976	71.09049656993335
1977	71.70349892850363
1978	73.42678181593591
1979	74.97868022845641
1980	76.42722837186903
1981	77.26776989798681
1982	77.8468595997627
1983	77.83264024319055
1984	77.76671784795988
1985	77.67455937348714
1986	77.22801028077642
1987	77.39002806004355
1988	50.094597728125436
1989	47.2316054079377
1990	22.56267409470752
1991	23.391812865497073
1992	22.397476340694006
1993	21.428571428571427
1994	22.382671480144403
1995	23.371647509578544
1996	24.796747967479675
1997	26.521739130434785
1998	26.666666666666668
1999	28.717948717948715
2000	31.147540983606557
2001	31.382978723404253
2002	31.606217616580313
2003	32.323232323232325
2004	32.84313725490196
2005	32.367149758454104
2006	32.093023255813954
2007	32.142857142857146
2008	31.601731601731604