Year	% of total
1971	0.8180160149602081
1972	0.8256156108359072
1973	0.8940470383002281
1974	1.0045206092431336
1975	1.1809883980394187
1976	1.3046187877054856
1977	1.2865247336566794
1978	1.2826109159700974
1979	1.3668832083872557
1980	1.221883818249968
1981	1.307579251862152
1982	1.469743261375884
1983	1.5957392113232989
1984	1.4497677326855138
1985	1.3925744417303845
1986	1.6741836947340882
1987	1.8578530630151833
1988	1.794738063931644
1989	1.7997446540227033
1990	2.0433614373743176
1991	2.2528673500261625
1992	2.6763643007977804
1993	2.596486474630729
1994	2.5042147105676102
1995	2.5087446613356756
1996	2.4340699976716604
1997	2.3616977676308197
1998	2.2044938006741774
1999	2.2449999174891127
2000	2.1773858295188755
2001	2.5043354464066416
2002	2.5790508500917806
2003	2.707426761990446
2004	2.7443704906540716
2005	2.8775412387933947
2006	2.810536646615326
2007	3.221093882881882
2008	3.1905310958305524
2009	3.562331940696225
2010	4.294701658249343
2011	4.380685719053606
2012	4.875593664744465
2013	5.4891109046440905
2014	6.523675782257906
2015	7.822693917795805