Year	% of total
1970	5.891450904548574
1971	6.155644175117225
1972	6.32732779227244
1973	6.217091949729494
1974	6.173623107384004
1975	6.163494805974783
1976	6.155337556564071
1977	6.156436075440489
1978	6.158194768451259
1979	6.207627255145642
1980	6.2348510635386285
1981	6.18457489869485
1982	6.323647467065972
1983	6.3603716602648115
1984	6.232791933432711
1985	6.249357603675174
1986	6.38306082330389
1987	6.327239882879083
1988	6.290465961091857
1989	6.384043782232646
1990	12.146722790138305
1991	13.038277511961722
1992	14.104116222760291
1993	14.476744186046512
1994	15.082527034718272
1995	15.197404002163331
1996	17.230609057782406
1997	19.143576826196472
1998	20.955165692007796
1999	22.63083451202263
2000	24.267399267399266
2001	24.830086089714545
2002	25.211581291759465
2003	25.524475524475527
2004	25.8147512864494
2005	26.1493040911008
2006	26.440116038126817
2007	26.959376282314324
2008	26.860326303223236