Year	% of total
1970	50.02273394755766
1971	48.88494296624504
1972	48.42780112990321
1973	48.77284002770257
1974	44.71277046272505
1975	46.37070381001915
1976	46.60608631148542
1977	49.005590847692005
1978	46.07304884250611
1979	46.50404648664024
1980	48.6931146482749
1981	45.01410053416671
1982	48.61509845279507
1983	45.416740530715934
1984	45.45445420385976
1985	43.57497670328076
1986	44.219734179106226
1987	44.802163252069924
1988	45.73748953693335
1989	45.87368931592851
1990	50.73891625615764
1991	48.205128205128204
1992	45.69892473118279
1993	44.148936170212764
1994	42.93193717277487
1995	38.7434554973822
1996	40.72164948453608
1997	44.18604651162791
1998	45.90163934426229
1999	41.17647058823529
2000	41.50197628458498
2001	37.75100401606426
2002	40.074906367041194
2003	39.92805755395683
2004	36.39705882352941
2005	44.23676012461059
2006	40.19933554817276
2007	37.15277777777778
2008	39.130434782608695