Year	% of total
1971	0.14435701077725205
1972	0.2756298094282449
1973	0.3088558652213903
1974	0.14429305443311383
1975	0.4646410051339114
1976	0.6128753529948469
1977	0.778754738569563
1978	1.0047925605156531
1979	1.4719232955921195
1980	2.005802805101795
1981	2.3789905650436536
1982	2.437125176941515
1983	3.023262558372285
1984	2.462800621595852
1985	2.515927087192035
1986	2.166777953644836
1987	2.559811547681149
1988	2.3143943910979257
1989	2.696738871757286
1990	2.963575699121575
1991	2.6679666267264306
1992	2.698404566654888
1993	2.765976068773577
1994	3.190840633788679
1995	2.8422595731875067
1996	3.070879307623332
1997	4.144384121876475
1998	3.9110986630772318
1999	4.2566140776180506
2000	3.888949634892121
2001	3.975170529871882
2002	4.965829404861511
2003	4.600069520061653
2004	5.4459633094025
2005	5.586053699068939
2006	5.657529191711184
2007	5.47355028105799
2008	5.329112045099187
2009	5.524018328881494
2010	6.786433499344921
2011	7.411568312031079
2012	7.756919170497079
2013	7.987258420447676
2014	8.591718959890638
2015	9.597514401579547