Year	% of total
1971	51.647908255962705
1972	53.2733426808558
1973	54.47647224110577
1974	56.783425943260326
1975	56.211775853442845
1976	57.58357870259808
1977	58.23172298102435
1978	57.299839192074174
1979	58.22910525235726
1980	58.881618940743806
1981	59.873611800576086
1982	60.05682361698954
1983	60.379295971159195
1984	61.99604041953495
1985	63.23915139035352
1986	62.100238848848434
1987	62.326675183946165
1988	61.90961108141777
1989	61.591441395897704
1990	62.80622290687936
1991	62.71329121230951
1992	62.537926497883824
1993	64.040663635214
1994	63.07805122592788
1995	62.84002798735562
1996	62.628703693143436
1997	61.65894162331753
1998	59.53045108341799
1999	58.549686937278636
2000	58.63730625488536
2001	55.007235791511974
2002	55.49647992268405
2003	54.29467109879705
2004	54.47000064731504
2005	55.24893328908976
2006	55.68546281586959
2007	54.68483733901394
2008	53.85166836167722
2009	54.01564273590461
2010	52.416088105417835
2011	53.26499998743757
2012	50.1689465792484
2013	47.84164073857716
2014	46.72962352445928
2015	44.029117304131205