Year	% of total
1970	22.54773064549957
1971	20.793925537867622
1972	20.937732551496943
1973	17.106337643634664
1974	15.260569539468028
1975	13.45648342303537
1976	12.149789447954683
1977	13.727369987100602
1978	12.673617590033246
1979	10.52047203596088
1980	12.814170149356668
1981	22.694052874565855
1982	21.91523876281847
1983	21.730454175331595
1984	18.761895264305995
1985	15.773645664171735
1986	13.710153374557517
1987	14.150858561550086
1988	13.122854640127446
1989	13.078327464357065
1990	40.998959417273674
1991	33.21637426900585
1992	36.353591160220994
1993	40.103092783505154
1994	40.54878048780488
1995	39.0495867768595
1996	32.795698924731184
1997	34.034034034034036
1998	33.96764985727878
1999	32.24907063197026
2000	30.85972850678733
2001	30.07181328545781
2002	30.175438596491226
2003	25.023084025854107
2004	26.465364120781526
2005	28.89637742207245
2006	28.908794788273617
2007	29.222309505106047
2008	29.02979373567609