Year	% of total
1990	3.12452705964144
1995	3.31428757779615
2000	3.54753384923502
2005	3.81539843032538
2010	4.02228175532646
2011	3.98327618220637
2012	3.90021890098856
2013	3.43309124418034
2014	2.4990981622518
2015	2.32287217279337
2016	1.98092209220901
2017	2.02022596178817