Year	% of total
1971	36.224906195062005
1972	36.207558394234916
1973	37.48217249736116
1974	37.51338182166391
1975	37.691313226685146
1976	38.368493388259765
1977	38.619935599088954
1978	39.5247498983258
1979	39.51057033830002
1980	40.36105366858343
1981	41.94229472506849
1982	43.212434312255205
1983	42.87379306215815
1984	43.17578876134424
1985	42.5786025686793
1986	42.42152125068773
1987	43.10055040252015
1988	42.844324314845764
1989	41.281174527014244
1990	40.650918124794096
1991	41.18037467181421
1992	39.4239648860884
1993	40.26172865973304
1994	39.14675343730118
1995	39.65136450140455
1996	39.418525740561336
1997	39.45457900155032
1998	38.55118960079543
1999	38.89943230778958
2000	38.23631543709161
2001	38.897670946872694
2002	38.01463961722678
2003	39.08267870120901
2004	39.90807248901161
2005	39.62651793791886
2006	38.93769166036472
2007	39.61722475471027
2008	40.96648795156824
2009	39.85679104045936
2010	39.59751226282024
2011	39.17406749768438
2012	38.702171961025776
2013	38.27411641824492
2014	39.78936584348551