Year	% of total
1970	35.686818541986064
1971	35.985382951693786
1972	37.17266649613906
1973	36.87137014917129
1974	38.69846760321576
1975	37.47107828419455
1976	38.83159079980863
1977	39.247469907488465
1978	39.54186548802857
1979	39.58826759202089
1980	40.98748656015051
1981	43.37923638216002
1982	43.259240691294096
1983	40.779107418523964
1984	40.306861545960615
1985	38.13295658414751
1986	38.83900963413996
1987	37.476218950933685
1988	37.887835310588756
1989	38.16616153973412
1990	3.968253968253968
1991	5.555555555555555
1992	7.575757575757576
1993	8.695652173913043
1994	9.722222222222223
1995	11.333333333333332
1996	11.03896103896104
1997	10.69182389937107
1998	10.429447852760736
1999	10.179640718562874
2000	9.941520467836257
2001	13.736263736263737
2002	16.580310880829018
2003	19.607843137254903
2004	21.86046511627907
2005	24.336283185840706
2006	23.770491803278688
2007	22.988505747126435
2008	22.58064516129032