Year	% of total
1971	14.612364977734387
1972	15.466373360840254
1973	16.653492077804888
1974	14.664368757370374
1975	16.401302622205638
1976	17.109780709114332
1977	22.344073855860888
1978	25.245397692286254
1979	23.746404117576933
1980	22.80286608025581
1981	21.308246681142197
1982	20.944724574255538
1983	19.038384954479014
1984	21.28773201533645
1985	21.60086665908148
1986	21.47363536582101
1987	20.255956871013215
1988	21.462809666882947
1989	19.730224195742657
1990	21.333649229255172
1991	20.14417155576599
1992	23.883743029032274
1993	26.570099854128532
1994	28.47486672540706
1995	29.524266111812768
1996	28.577168226846545
1997	29.13696858530027
1998	30.96400690513007
1999	32.435096288817114
2000	28.200423037634557
2001	28.787062764806926
2002	30.513620433339174
2003	30.972866436254204
2004	31.11406859872538
2005	29.009378744963044
2006	30.105518981186574
2007	30.254176685477752
2008	30.01931930694186
2009	30.709850111597227
2010	32.580288551036176
2011	33.63711166996936
2012	33.81693460286254
2013	33.61510405492384
2014	33.70331204509327