Year	Percent change (Units)
1998	15.726
1999	0.581
2000	-28.317
2001	40.060
2002	-28.448
2003	10.891
2004	-3.271
2005	-19.903
2006	-35.169
2007	-29.104
2008	-20.541
2009	51.989
2010	-5.382
2011	-12.809
2012	5.103
2013	2.117
2014	27.855
2015	6.396
2016	-11.422
2017	-3.285
2018	11.736
2019	3.701