Year	% of total
1970	50.72262437164395
1971	50.799652834900556
1972	51.428962186201296
1973	49.23076420279983
1974	47.9923115891745
1975	47.2619605765707
1976	46.18425854037046
1977	45.94016765184936
1978	45.58722830473451
1979	45.26578042190928
1980	44.16434201546494
1981	43.18201737205163
1982	43.50122183315167
1983	42.193662484846506
1984	40.95757939575713
1985	39.126089939780094
1986	39.47040960243752
1987	38.73662176495622
1988	37.97121676822332
1989	38.196396958003675
1990	45.11609287429944
1991	43.32730560578662
1992	41.45370063060073
1993	39.4435857805255
1994	37.62662807525325
1995	35.85266030013642
1996	34.47388731669668
1997	33.9513604623164
1998	31.016670579948347
1999	31.83993040452371
2000	31.204794379003925
2001	30.58433485288023
2002	32.10473313192346
2003	32.09925955573344
2004	32.396039603960396
2005	32.24852071005917
2006	32.48322147651007
2007	32.83054003724395
2008	32.54794520547945