Year	% of total
1970	19.153594352069476
1971	19.074718920024893
1972	20.174228447291608
1973	20.6280630380579
1974	21.21709452967659
1975	20.610122934003563
1976	20.28665362218926
1977	19.712894196283763
1978	19.81588912007868
1979	19.791357095826296
1980	19.867246014964056
1981	20.54896142985862
1982	19.57778800937882
1983	20.682988559337375
1984	20.573147195622752
1985	20.100128001025162
1986	19.318399986384705
1987	18.479129146713234
1988	18.80179503851071
1989	18.185339205730003
1990	6.295754026354319
1991	6.276747503566334
1992	6.406685236768802
1993	6.377204884667571
1994	6.490066225165562
1995	6.657963446475196
1996	6.390977443609022
1997	6.398996235884567
1998	6.4638783269961975
1999	6.107784431137724
2000	5.788876276958002
2001	5.950991831971995
2002	6.310679611650485
2003	6.6167290886392
2004	6.155632984901278
2005	6.081081081081082
2006	6.004366812227074
2007	6.263982102908278
2008	6.216505894962487