Year	% of total
1970	11.562800889145844
1971	11.987019988133566
1972	12.913820486739
1973	13.297444446437702
1974	13.699290277677342
1975	14.113646230079013
1976	14.924746376063966
1977	15.770318450798154
1978	16.486468479676216
1979	16.054754122045896
1980	16.237859153075163
1981	16.35605452989465
1982	17.59153944551343
1983	17.407551936494382
1984	17.091475074090205
1985	17.548466335747136
1986	18.08133830084667
1987	17.776505803792684
1988	18.74165791422952
1989	18.573988112157043
1990	21.346647417388514
1991	21.933218973151952
1992	22.648924166374847
1993	23.07956759234501
1994	23.199792461920467
1995	23.5725549158385
1996	23.533823844560324
1997	24.399328123858908
1998	24.83236394620828
1999	24.41303938194837
2000	24.56848923604496
2001	24.18052070263488
2002	23.87445633008111
2003	22.99469353226179
2004	22.658937198067633
2005	21.974954445004457
2006	20.895005959017336
2007	19.260131414030155
2008	19.444556410979885