Year	% of total
1970	35.225546043501524
1971	34.876582137178644
1972	34.8596248723227
1973	34.4200729935061
1974	34.624573456164015
1975	34.85917824419022
1976	34.79330149915296
1977	34.96557002518536
1978	35.01207757507035
1979	34.80398160302682
1980	35.1833872676971
1981	35.20451199840985
1982	35.78541979302057
1983	35.911275334569325
1984	34.199026286073014
1985	32.479570510469244
1986	31.096184040081464
1987	29.68864472470523
1988	29.245588583882657
1989	29.454400788782483
1990	51.83431952662721
1991	50.712589073634206
1992	51.405152224824356
1993	52.5383707201889
1994	53.41317365269461
1995	52.80487804878049
1996	52.933985330073355
1997	53.20987654320988
1998	53.037974683544306
1999	53.65535248041775
2000	53.76344086021505
2001	53.76196990424077
2002	54.94350282485876
2003	55.74963609898108
2004	55.9593023255814
2005	57.14285714285714
2006	57.71604938271605
2007	58.87096774193549
2008	61.694915254237294