Year	% of total
1970	6.430273863384523
1971	6.704639659785061
1972	7.114070175719661
1973	6.979551470933293
1974	7.905307332113022
1975	7.17252113243325
1976	7.191462858497275
1977	6.627633177894021
1978	7.280008641007295
1979	7.083502854809782
1980	6.214459545332242
1981	6.324330862052051
1982	5.996883166787499
1983	6.257254101810612
1984	6.37593531207329
1985	6.520783627528187
1986	6.651860936667642
1987	6.590733159637111
1988	6.617982654593504
1989	6.450331452990872
1990	13.777777777777779
1991	13.779718583212034
1992	13.733905579399142
1993	13.558537714021288
1994	13.520871143375683
1995	13.816381638163817
1996	13.697442566103163
1997	13.647851727042964
1998	13.125739061884115
1999	13.294346978557506
2000	13.461538461538462
2001	13.943768996960488
2002	14.3928035982009
2003	14.38823107283818
2004	14.901960784313726
2005	14.418296320848526
2006	14.409317803660565
2007	14.605978260869565
2008	14.295257181028726