Year	% of total
1970	3.7197257174067277
1971	3.696655298221194
1972	3.7821439425227346
1973	3.9044876822116867
1974	3.9960947823626127
1975	4.057433334395397
1976	4.164840104104344
1977	4.119747706754687
1978	4.4704773406203175
1979	4.459458403450744
1980	4.654209198270282
1981	4.641935709722307
1982	4.512622246148075
1983	4.317118770630214
1984	4.285679643465723
1985	4.141632972417608
1986	4.806213689818072
1987	4.3373315583682395
1988	4.527210798821792
1989	4.60505105556168
1990	3.9671682626538987
1991	4.232505643340858
1992	4.284103720405862
1993	4.254727474972191
1994	4.324923759356806
1995	4.401805869074492
1996	4.39469320066335
1997	4.496253122398001
1998	4.477211796246649
1999	4.547945205479452
2000	4.612445414847162
2001	4.5331894225580145
2002	4.8588885656095435
2003	4.899713467048711
2004	5.0745412844036695
2005	4.953979426096373
2006	5.126073704627321
2007	5.15519568151147
2008	5.204872646733112