Year	% of total
1971	33.87287042544843
1972	34.00650275790639
1973	34.26186735821213
1974	35.33817731969892
1975	35.7247529150918
1976	36.41454650675107
1977	36.88531286245767
1978	36.11191817071369
1979	37.593417791786884
1980	38.36126077312222
1981	40.313285440615864
1982	41.92255910024651
1983	42.67916751468809
1984	43.74822828163245
1985	45.674465840063554
1986	46.622665758400956
1987	48.34842163216719
1988	49.75859577336594
1989	51.24460956250581
1990	52.14725919540592
1991	53.2204307908594
1992	54.26389704788097
1993	55.29819456488767
1994	56.273458274024954
1995	58.18549369435192
1996	59.10565166748466
1997	59.939664808149665
1998	60.17093586959014
1999	61.60024492875795
2000	61.82295582576192
2001	61.806240733524874
2002	62.328084391091494
2003	62.58626422578699
2004	63.63679312166997
2005	64.04593451269635
2006	64.88514028480125
2007	66.04972487154693
2008	67.03846247953574
2009	68.9359300142452
2010	69.18918430965476
2011	69.3130540828319
2012	70.22646035013622
2013	70.04817635399932
2014	71.52352350899726