Year	% of total
1990	18.5196017423926
1995	17.7755056559668
2000	18.5559663630583
2005	19.1221678810919
2010	18.2176168049473
2011	16.7921293693532
2012	22.3585305257646
2013	13.9561608125261
2014	16.1903842592858
2015	8.32906961362858
2016	4.94687413039807
2017	4.49774701574109