Year	% of total
1970	4.943166024230973
1971	5.105733235056685
1972	4.985581676676546
1973	5.093162229580987
1974	4.959195685420022
1975	5.106861548886608
1976	4.663517986230067
1977	4.286372462797754
1978	4.411934492467748
1979	4.489939487510609
1980	5.23204726574914
1981	5.422522820601622
1982	5.542905609363135
1983	5.87668204818321
1984	6.346774225794198
1985	6.514247226208967
1986	6.64324516293121
1987	6.831474766927266
1988	7.747978100263851
1989	8.766199349248987
1990	11.302211302211303
1991	12.090680100755668
1992	12.661498708010335
1993	13.720316622691293
1994	14.666666666666666
1995	15.089514066496163
1996	15.802469135802468
1997	16.040100250626566
1998	15.328467153284672
1999	17.391304347826086
2000	17.874396135265698
2001	19.4300518134715
2002	15.49636803874092
2003	15.8311345646438
2004	15.69620253164557
2005	17.232375979112273
2006	17.759562841530055
2007	16.79790026246719
2008	17.20430107526882