Year	Percent change (Units)
1980	19.332
1981	18.400
1982	14.274
1983	5.987
1984	9.453
1985	16.818
1986	36.187
1987	71.429
1988	30.000
1989	15.385
1990	11.111
1991	9.000
1992	11.100
1993	13.200
1994	15.328
1995	7.722
1996	8.872
1997	1.889
1998	-0.953
1999	-3.700
2000	-3.900
2001	3.401
2002	-0.518
2003	5.797
2004	4.433
2005	7.240
2006	10.390
2007	4.677
2008	15.153
2009	2.804
2010	4.398