Year	% of total
1971	2.0028118930534093
1972	2.517519756976038
1973	3.1178248145310454
1974	3.954240189159292
1975	5.336416444008521
1976	5.751636463587371
1977	6.777943484490074
1978	7.5556746760407645
1979	7.451590077015926
1980	7.8059285276132595
1981	9.034592431375213
1982	9.635967292567495
1983	10.490088762559195
1984	11.95275828045246
1985	13.647005534318584
1986	14.418345603344932
1987	14.797507183829284
1988	15.284953782993158
1989	14.896029496114386
1990	16.91081425433462
1991	17.298216198072822
1992	17.294260547653106
1993	17.42067290790556
1994	17.405635007463577
1995	17.501796716838292
1996	17.583602240995745
1997	17.046995012942773
1998	16.97550712924057
1999	17.0848825776904
2000	16.703650946349317
2001	16.87798347469922
2002	16.384221123443783
2003	15.656158982074286
2004	15.551744684525277
2005	15.071327524003147
2006	14.63263395379942
2007	13.662398681822301
2008	13.475271489089646
2009	13.344124533972165
2010	12.786946448741638
2011	11.604177576256493
2012	10.811499665050166
2013	10.580146594433884
2014	10.601443939971308
2015	8.113442226260027