Year	% of total
1971	0.3507790879675622
1972	0.3234808382806171
1973	0.3191154847827604
1974	0.25734548004839924
1975	0.2738863817177653
1976	0.25428452687197
1977	0.25912667202130774
1978	0.26224263291679034
1979	0.2602748066232839
1980	0.31237924073486667
1981	0.3226174966662313
1982	0.2874423342607445
1983	0.2904635401960784
1984	0.2966244223900792
1985	0.3027201018110173
1986	0.3245635895596907
1987	0.3076560548632371
1988	0.3181805373849288
1989	0.3148642999742051
1990	0.43677811767346864
1991	0.4617439299909075
1992	0.5104499564477623
1993	0.5821925271507942
1994	0.6499245791427568
1995	0.7177631512323893
1996	0.7302880102146699
1997	0.8987007792543961
1998	1.0616157255397183
1999	1.1587521848462825
2000	1.383598966569969
2001	1.505448231600288
2002	1.8165258383178704
2003	2.1050479048640396
2004	2.5796176101336763
2005	2.976332333076033
2006	3.3686529687379103
2007	3.9654445597749195
2008	4.485777304291971
2009	5.3241071900006105
2010	5.909014175182729
2011	7.186542308005829
2012	8.397362289295753
2013	9.537717457783252
2014	10.461958890839721
2015	11.781898935512231