Year	% of total
1971	54.198078177145824
1972	56.77875512221885
1973	55.9001637572647
1974	62.192407137538844
1975	60.49938798846461
1976	59.625744238212555
1977	57.875627739480464
1978	53.84500164401502
1979	52.43840748731981
1980	49.60988406571837
1981	50.45914318205513
1982	47.57928835153111
1983	42.94371267595398
1984	40.619600551162485
1985	41.92603239647724
1986	40.607752948644276
1987	40.92744176009439
1988	42.089577680632864
1989	42.29481159223271
1990	42.07798852735864
1991	44.484703026768976
1992	39.67821382954678
1993	39.50716635871707
1994	37.424956890115055
1995	37.03891772914551
1996	36.45515080159369
1997	35.75810066134805
1998	39.45819943318594
1999	39.0166050252115
2000	39.422720457778695
2001	41.40097322056272
2002	41.10983194018078
2003	42.4724111917594
2004	39.634998629627106
2005	44.973353759236865
2006	43.18827116825644
2007	44.11444831066243
2008	40.70817964440383
2009	40.717392613679806
2010	39.900478627480815
2011	37.57108685878222
2012	38.410101748317366
2013	36.03254458545124
2014	33.749348688738564
2015	32.431549405276556