Year	% of total
1971	28.676947668175078
1972	25.856888260449967
1973	24.01619181436819
1974	24.001860540407865
1975	24.771679170188442
1976	22.910241540467535
1977	25.12280115271856
1978	25.819960884354
1979	25.35667365522266
1980	26.06129247417256
1981	26.49062178610011
1982	27.80936062655982
1983	29.163043286191627
1984	31.985174329621053
1985	35.25143591782189
1986	37.022888906070484
1987	38.04337740106908
1988	38.30657569399006
1989	38.49268117624912
1990	37.8204947700643
1991	39.17465623591897
1992	41.023533777386845
1993	41.88856338498098
1994	42.727115154421426
1995	42.91851285027136
1996	44.60447947842463
1997	45.27699883526424
1998	45.89993263256023
1999	47.492635938366966
2000	49.37774525441675
2001	50.52603452853508
2002	51.9246375448386
2003	54.78212737915774
2004	55.167495978637604
2005	56.980959233394465
2006	58.77960504590371
2007	60.55239655752974
2008	59.97198041148576
2009	60.68459662297524
2010	60.10899988826864
2011	62.539677209806946
2012	61.57036850262316
2013	62.01227527048426
2014	60.43218528998936
2015	59.367057733810114