Year	% of total
1960	46.54649506862647
1961	46.361176768013706
1962	47.06917392122913
1963	47.220665473797375
1964	46.7469361592799
1965	46.21714824699323
1966	45.154281996080826
1967	44.88014423667566
1968	44.36248388004208
1969	42.09929139014859
1970	39.83079141157994
1971	39.08342879923806
1972	37.29437087708172
1973	37.51800041506501
1974	35.89546247143255
1975	36.19477997969804
1976	37.83580541937648
1977	37.59020169982861
1978	36.54186714429743
1979	38.00976974040146
1980	40.44331389637956
1981	40.894713310207706
1982	41.76767802141765
1983	42.290416266968826
1984	41.6490151221361
1985	42.346338325150946
1986	41.73945415845744
1987	41.93212115083286
1988	41.59975471106084
1989	40.58833611549224
1990	39.75628613449477
1991	39.31070618053956
1992	39.041732712657655
1993	38.72643300562698
1994	38.216991686780204
1995	37.7625015461838
1996	38.29532443166574
1997	38.32739129123429
1998	38.26543975286754
1999	37.633985019368595
2000	38.453848923800706
2001	37.87412574464081
2002	37.672734672387065
2003	38.27713983549301
2004	37.3302478016985
2005	37.24787236155841
2006	36.89056533374409
2007	36.60735827293429
2008	35.798567200973544
2009	34.10119160652118
2010	33.92681071075387
2011	33.015413997259344
2012	31.833373226133
2013	32.26406024910081
2014	31.79119092445531
2015	29.443466906612752