Year	% of total
1971	33.872870425448426
1972	34.00650275790639
1973	34.261867358212136
1974	35.33817731969892
1975	35.724752915091806
1976	36.41454650675107
1977	36.88531286245767
1978	36.11191817071369
1979	37.593417791786884
1980	38.36126077312222
1981	40.31328544061586
1982	41.92255910024651
1983	42.67916751468809
1984	43.74822828163245
1985	45.67446584006356
1986	46.622665758400956
1987	48.34842163216718
1988	49.75859577336593
1989	51.24460956250581
1990	52.147259195405915
1991	53.22043079085939
1992	54.26389704788097
1993	55.29819456488766
1994	56.273458274024954
1995	58.185493694351926
1996	59.10565166748465
1997	59.93966480814967
1998	60.17093586959014
1999	61.60024492875795
2000	61.82295582576192
2001	61.806240733524874
2002	62.32808439109148
2003	62.58626422578698
2004	63.63679312166995
2005	64.04593451269636
2006	64.88514028480125
2007	66.04972487154694
2008	67.03846247953574
2009	68.93593001424519
2010	69.18918430965476
2011	69.3130540828319
2012	70.22646035013621
2013	70.04817635399932
2014	71.52352350899724