Year	% of total
1971	0.144357010777252
1972	0.27562980942824483
1973	0.3088558652213902
1974	0.1442930544331138
1975	0.4646410051339112
1976	0.6128753529948466
1977	0.7787547385695627
1978	1.004792560515653
1979	1.4719232955921189
1980	2.005802805101794
1981	2.378990565043653
1982	2.4371251769415143
1983	3.0232625583722843
1984	2.462800621595851
1985	2.515927087192034
1986	2.1667779536448353
1987	2.5598115476811483
1988	2.314394391097925
1989	2.6967388717572858
1990	2.9635756991215745
1991	2.66796662672643
1992	2.6984045666548875
1993	2.7659760687735764
1994	3.190840633788678
1995	2.8422595731875058
1996	3.070879307623331
1997	4.144384121876474
1998	3.911098663077231
1999	4.25661407761805
2000	3.88894963489212
2001	3.9751705298718814
2002	4.96582940486151
2003	4.600069520061653
2004	5.445963309402499
2005	5.586053699068938
2006	5.657529191711182
2007	5.47355028105799
2008	5.329112045099186
2009	5.5240183288814935
2010	6.786433499344921
2011	7.411568312031077
2012	7.756919170497077
2013	7.9872584204476755
2014	8.591718959890638
2015	9.597514401579547