Year	% of total
1970	3.4983493237143546
1971	3.6975062700951384
1972	3.7656117510451494
1973	3.9025993088405464
1974	3.9548084810920403
1975	3.923185840042383
1976	4.12420511328701
1977	4.256275274879737
1978	4.285173637752918
1979	4.342932556898043
1980	4.696978179429826
1981	4.720663601884054
1982	4.918602473343491
1983	5.314688714618834
1984	5.339249745166989
1985	5.490347748836649
1986	5.642665268610201
1987	5.982602389747658
1988	6.298625533591961
1989	6.428490364549552
1990	3.05995650823237
1991	3.0716723549488054
1992	3.0438124519600307
1993	3.05542760632581
1994	3.017895056111617
1995	3.089845507724614
1996	3.2107325896894787
1997	3.2875074716078903
1998	3.4150744696855724
1999	3.423555230431602
2000	3.4812880765883376
2001	3.5978528942405337
2002	3.602449095827994
2003	3.631245601688952
2004	3.718365615721759
2005	3.7037037037037033
2006	3.7668895864610343
2007	3.8274276440357045
2008	3.8079036901334726