Year	% of total
1971	39.83532982589198
1972	39.469635560450065
1973	39.26281652984452
1974	38.160093561770736
1975	38.23619982074323
1976	37.873830500502784
1977	37.77050695490998
1978	38.14590904481355
1979	37.869043664916056
1980	37.70558027553955
1981	37.18282243847578
1982	37.35823450446563
1983	37.487437756222455
1984	37.34124565651793
1985	37.4845638456163
1986	37.869194017890415
1987	38.45739535135376
1988	37.936427331713965
1989	38.45279204696537
1990	69.24940505472492
1991	68.99689638949505
1992	68.80260574309483
1993	67.87148003427848
1994	67.53563056823057
1995	67.47224455874637
1996	67.95313221939429
1997	68.17400739854918
1998	68.16956106105621
1999	68.82653581112622
2000	69.40374885637706
2001	69.59664362007632
2002	70.26772666152883
2003	71.4383428814431
2004	71.09631816590868
2005	71.12852592399977
2006	71.68792354910757
2007	72.70057760124152
2008	72.45215097259018
2009	72.26995289351265
2010	72.13499853337447
2011	72.98057104758604
2012	72.11542630232198
2013	71.81664538351298
2014	70.96976802369362
2015	70.33914854261606