Year	% of total
1990	3.7357358229711113
1991	3.764551032867632
1992	3.808429821210626
1993	3.699479366105446
1994	3.6960867695650492
1995	3.994081441660702
1996	4.572536187791727
1997	5.107085163293823
1998	5.735851073112681
1999	6.741263037503994
2000	7.773415259478342
2001	7.509604908535888
2002	7.482350151410829
2003	7.574039438183955
2004	7.445500752577634
2005	8.019556244510479
2006	8.358134762071405
2007	8.699183527860841
2008	8.960470619084813