Year	% of total
1970	30.991211869030888
1971	31.04723427298567
1972	31.384221500535652
1973	31.822777508296756
1974	32.274930547788124
1975	32.66988679615502
1976	32.685708698420605
1977	33.03872665411123
1978	33.38311565500035
1979	33.10457318260671
1980	33.084817136796914
1981	33.32885867026402
1982	33.6504607717457
1983	34.74551001233287
1984	35.568212534580134
1985	35.18764187115397
1986	35.80648192325203
1987	36.12743243868587
1988	36.26137204731395
1989	36.155990326298706
1990	39.55626472152572
1991	38.24409448818898
1992	36.3720228111372
1993	35.31792882442233
1994	36.32925864040102
1995	36.77390527256479
1996	37.45177291934595
1997	38.56749311294766
1998	39.73169255598144
1999	39.441624365482234
2000	40.33577728190416
2001	42.278338945005615
2002	43.64985862393968
2003	44.73978387777916
2004	47.00120756742251
2005	49.29936305732484
2006	51.049160671462836
2007	52.96952736318408
2008	54.637065029129275