Year	% of total
1970	6.220915524723524
1971	6.043780705319058
1972	5.742225190990276
1973	6.412143125773895
1974	5.7437533237458105
1975	6.2724168979920645
1976	6.3323798499716695
1977	6.322136142382926
1978	6.590928063463419
1979	6.834345422897716
1980	6.99697177730786
1981	7.28970529709224
1982	6.934683548188627
1983	6.96695296696762
1984	7.1911036490773075
1985	7.971487224307347
1986	8.45883858560402
1987	8.898325755131422
1988	8.755733289521473
1989	8.819140420281427
1990	6.982248520710059
1991	7.363420427553444
1992	7.142857142857142
1993	7.201889020070838
1994	7.3053892215568865
1995	7.439024390243902
1996	7.701711491442542
1997	7.28395061728395
1998	7.215189873417721
1999	7.049608355091384
2000	7.123655913978495
2001	7.113543091655266
2002	7.344632768361582
2003	7.5691411935953425
2004	7.703488372093023
2005	7.969924812030076
2006	7.87037037037037
2007	8.225806451612904
2008	8.47457627118644