Year	% of total
1971	0.2517750899113118
1972	0.24696381213957924
1973	0.263438878840295
1974	0.24653997020663135
1975	0.2692179255641891
1976	0.27727204259055
1977	0.2819266571766112
1978	0.27422495295530525
1979	0.3024294911788737
1980	0.3491960718805966
1981	0.3804352139996877
1982	0.48201508735180837
1983	0.5174597118670871
1984	0.5357660246222193
1985	0.5604069174219762
1986	0.5992251712026837
1987	0.6039984623117631
1988	0.6034460913205043
1989	1.1090519224901085
1990	1.3112778021210454
1991	1.0301201448458606
1992	1.1300497636098192
1993	1.1449678103700265
1994	1.1766337748445286
1995	1.1823492643629963
1996	1.178749272703169
1997	1.2233641106362743
1998	1.2512408244790492
1999	1.3244768437255126
2000	1.399771059778943
2001	1.4362780425693218
2002	1.5595126667413601
2003	1.6506951110168835
2004	1.795900562008952
2005	1.9564370721140187
2006	2.1247287482704595
2007	2.3485740453029043
2008	2.6791881891341927
2009	3.1270531296793345
2010	3.5510084319510344
2011	4.095887576709136
2012	4.692838195088532
2013	5.407781464282441
2014	6.003371426814834
2015	6.761825460314862