Year	% of total
1970	44.21940059168153
1971	44.56335252244516
1972	43.12440898196673
1973	41.53541319384568
1974	41.102431184673094
1975	41.277386773738684
1976	42.73822387675306
1977	42.167500886243204
1978	42.90987760644502
1979	43.39501706917891
1980	44.05719203087514
1981	43.98877886265897
1982	46.86570574344724
1983	47.753199238065164
1984	49.32162166180195
1985	52.615754308669175
1986	51.17550134013628
1987	53.34099351658422
1988	52.05269899557189
1989	52.91344340857144
1990	66.12244897959184
1991	65.17311608961303
1992	65.74468085106383
1993	64.08602150537635
1994	64.78260869565217
1995	63.39869281045751
1996	63.11300639658849
1997	62.93103448275862
1998	62.20302375809935
1999	61.33909287257019
2000	60.130718954248366
2001	61.88340807174888
2002	60.689655172413794
2003	58.75576036866359
2004	67.54617414248021
2005	67.36842105263158
2006	66.57824933687002
2007	65.84699453551912
2008	65.4353562005277