Year	% of total
1970	4.531359964538208
1971	4.6906828237464255
1972	5.036640620509339
1973	4.905446929604765
1974	4.441224313527281
1975	5.244151683138383
1976	5.110768324611662
1977	4.6146293538087235
1978	4.510033679385205
1979	4.686233082157317
1980	5.132494338343812
1981	5.082535168920196
1982	5.542442584497131
1983	5.463758809368649
1984	5.015073953044799
1985	5.022723399553989
1986	5.244181031676914
1987	5.913947331497072
1988	5.198005647982578
1989	5.7177401417023574
1990	8.804347826086957
1991	9.325287986834887
1992	9.51362907536077
1993	9.702660406885759
1994	9.95850622406639
1995	10.16949152542373
1996	11.25748502994012
1997	12.131596984235777
1998	14.249146757679181
1999	15.694164989939638
2000	18.985695708712612
2001	20.105124835742444
2002	20.561941251596423
2003	20.559610705596107
2004	22.33502538071066
2005	21.49532710280374
2006	21.83507549361208
2007	22.576832151300234
2008	21.2882096069869