Year	% of total
1971	11.703517884341089
1972	11.548603195216073
1973	10.484302884651523
1974	11.372404571724498
1975	12.593995942865904
1976	14.136232075169572
1977	14.603379736076997
1978	16.264395526144558
1979	18.690036508398265
1980	20.285910708952635
1981	21.396120570377445
1982	21.80121087050924
1983	22.301773638920768
1984	28.55344050560283
1985	29.39792872091531
1986	29.135183962189675
1987	28.360710755764163
1988	28.527796857752147
1989	28.581460334788083
1990	30.612254218165564
1991	31.346531469732085
1992	35.87804573993505
1993	40.59922031111209
1994	40.93432943084945
1995	41.72812817530742
1996	42.86822554774867
1997	43.136491034727115
1998	44.03948859828866
1999	43.309543948789354
2000	43.54575991858958
2001	44.521440877745825
2002	44.86558306532599
2003	44.59854366570906
2004	45.42595573450607
2005	47.71055003983809
2006	48.79655565006581
2007	48.1612828979522
2008	48.14654019488647
2009	49.96114013964355
2010	49.686014750169306
2011	51.60050345288083
2012	53.265704685687254
2013	52.333613337266286
2014	54.1556792314618
2015	55.91874388308216