Year	% of total
1970	52.23142875267107
1971	53.612341578703074
1972	53.39494150113847
1973	52.90145866956717
1974	53.5095717814984
1975	53.49092292003116
1976	52.84179807575339
1977	52.76808493969292
1978	53.06089206390073
1979	53.12509299334649
1980	52.24483065364522
1981	51.34825038306441
1982	51.45588783508451
1983	51.532319428506135
1984	51.63486715559261
1985	51.26513674355254
1986	51.078198719898595
1987	50.93429754743634
1988	48.91053390383973
1989	48.778211357088594
1990	56.7847882454624
1991	56.99391833188532
1992	56.80212014134276
1993	56.32393084622384
1994	57.39868049010367
1995	56.81818181818182
1996	58.03842264914054
1997	58.91553701772679
1998	59.183673469387756
1999	59.86913849509269
2000	60.29082774049217
2001	60.79545454545454
2002	60.75949367088608
2003	60.14067995310668
2004	59.71563981042654
2005	60.99635479951397
2006	61.41439205955335
2007	62.43654822335025
2008	63.67137355584083