Year	% of total
1970	16.678655710603934
1971	16.61389626016595
1972	16.79786604611105
1973	16.5551454592861
1974	14.2239275473198
1975	13.997012613737315
1976	14.329168259661781
1977	14.463975799640066
1978	14.90585300178526
1979	14.829374015977153
1980	15.394450424076386
1981	15.597384931203932
1982	16.81751894512596
1983	16.520336291706926
1984	16.472353592038445
1985	16.535458690613638
1986	16.79366212281121
1987	16.979972836377673
1988	17.825825574318472
1989	17.998775439918973
1990	10.184049079754601
1991	12.379421221864952
1992	12.748344370860929
1993	13.893967093235831
1994	13.274336283185843
1995	13.556338028169016
1996	13.969335604770016
1997	14.590747330960854
1998	14.928057553956833
1999	16.0075329566855
2000	12.704174228675136
2001	12.1160409556314
2002	14.92842535787321
2003	15.461847389558233
2004	15.192307692307692
2005	15.789473684210526
2006	16.6
2007	17.09741550695825
2008	17.20647773279352