Year	% of total
1990	15.552282122747528
1991	16.289546287616158
1992	16.816299678568395
1993	17.439591643593143
1994	17.812146879061668
1995	17.922645505939744
1996	18.14888289402619
1997	18.00648082379953
1998	17.530030881574774
1999	17.50467527824898
2000	17.562974137095896
2001	18.443290016695325
2002	18.28684487346925
2003	18.394879041962522
2004	18.82885968975729
2005	18.742139591989726
2006	19.65107498229184
2007	19.918003322330208
2008	20.182066501322392