Year	% of total
1970	11.39091529658629
1971	11.60960678189178
1972	12.024839242346161
1973	12.497574369708744
1974	13.575516396046842
1975	14.34867988624941
1976	14.942231001311596
1977	14.956822305201278
1978	15.123663463651107
1979	15.421834000756155
1980	15.505825881315289
1981	15.709640400421756
1982	15.921713286607615
1983	16.258165522538377
1984	16.0152506906176
1985	16.350755640808472
1986	16.94397994513337
1987	17.345662503890356
1988	17.583781723019186
1989	18.00722857962874
1990	20.65615835777126
1991	21.31913303437967
1992	21.379181461409082
1993	21.366553416383542
1994	20.834900338473112
1995	20.525917517972
1996	19.9288256227758
1997	19.847470238095237
1998	20.082505156572285
1999	19.691555388376905
2000	18.647845468053493
2001	18.285163776493256
2002	17.423076923076923
2003	18.164138467522363
2004	17.170712296060486
2005	18.17095038852361
2006	17.606350498676978
2007	18.383550488599347
2008	19.176971416987634