Year	% of total
1971	45.14797296248539
1972	43.64854853922639
1973	42.37265691583576
1974	39.50115154853016
1975	39.30210049787226
1976	37.905932959849665
1977	37.711914625450945
1978	38.267967848091786
1979	37.44857463507999
1980	37.12079681092991
1981	35.95159711484241
1982	35.8849258827149
1983	35.11555895635992
1984	33.080015465016835
1985	31.399663622373758
1986	33.02161582786247
1987	32.40013140060648
1988	33.10621386843992
1989	33.331913108003505
1990	30.853702636318797
1991	30.729794719138788
1992	30.447540824405024
1993	29.051321220069255
1994	30.2671497840999
1995	29.912987680100112
1996	30.31681864986804
1997	31.16206372891045
1998	33.7109178000515
1999	34.547878304522186
2000	34.714598595414195
2001	37.00695334096926
2002	36.24954534551274
2003	37.29604644486358
2004	37.435372642729305
2005	36.860381734973764
2006	36.369575081510135
2007	37.191543309611525
2008	38.18158065713802
2009	37.523637472379725
2010	38.87278214724506
2011	37.77957382752203
2012	40.54278263046703
2013	42.19096954390024
2014	42.52226892359786
2015	43.81112990599435