Year	% of total
1971	3.176125129146491
1972	2.745782452434252
1973	2.4696429873447596
1974	2.2475702662919215
1975	2.007050865849448
1976	1.9228050434874873
1977	1.8500048527972446
1978	2.1907190036238733
1979	2.0448501404885358
1980	2.1033600890722086
1981	2.3672745550953294
1982	2.3812861707904687
1983	2.3730462626892086
1984	2.839908898261736
1985	3.0143400663043494
1986	3.45752035789739
1987	3.410871416699339
1988	3.609357002857171
1989	3.8706678284855514
1990	3.8287283887509482
1991	3.7547867267995194
1992	3.4689761225660845
1993	3.623102834164672
1994	4.0487361274454114
1995	4.32592676097153
1996	4.660167033277094
1997	4.652723332698147
1998	4.55043679077043
1999	4.788425055914667
2000	4.35103451405876
2001	4.432802715106001
2002	4.491592795660038
2003	4.7822143972995805
2004	4.365598039628922
2005	4.994075191578799
2006	5.037742775301782
2007	5.07514999171754
2008	4.263513998763151
2009	4.781388018097658
2010	5.124961275322406
2011	5.18819805621097
2012	5.709719447540377
2013	6.409441557366742
2014	6.467101185271383
2015	6.684506878565062