Year	% of total
1971	43.86904197488248
1972	42.15952972182422
1973	40.67901045157626
1974	37.99285059132548
1975	38.2096370216782
1976	36.89159502278467
1977	37.03626015911356
1978	37.27834967570452
1979	35.70928394468115
1980	35.028392476555766
1981	33.45575872908228
1982	33.83310382416542
1983	33.31228527203764
1984	31.403270097896772
1985	29.95954917725821
1986	32.317335617019474
1987	32.28123323439394
1988	32.81455955693875
1989	32.62868861433565
1990	30.155458063863094
1991	31.37140543202951
1992	31.523001835614796
1993	29.669193300032926
1994	31.282030264688128
1995	30.412457907387992
1996	30.48324934520225
1997	31.774768458971476
1998	33.99761133047055
1999	34.636857388663536
2000	35.375105322836205
2001	37.69905702487165
2002	36.707775797005766
2003	37.594066551939434
2004	37.99309512538063
2005	37.995774887562774
2006	37.3523350029457
2007	37.76243594728991
2008	38.88269888789008
2009	38.180950230949584
2010	39.027021079087504
2011	37.787758982602604
2012	40.52038750445523
2013	42.59298140940405
2014	43.563662879960035
2015	44.662703075339024