Year	% of total
1990	16.5975324783366
1995	15.3066784600369
2000	15.0870713291621
2005	9.75075011707954
2010	15.0929781723734
2011	19.9140586589907
2012	24.2957499965468
2013	21.2419781952346
2014	21.5226325115215
2015	21.3922855178398
2016	20.9578121048987
2017	20.8324237472538