Year	Number
1979	21.64634
1980	21.59373
1981	21.49424
1982	21.65362
1983	21.66796
1984	21.49753
1985	21.13167
1986	20.94499
1987	21.00578
1988	21.03189
1989	20.94175
1990	20.95969
1997	19.45607
1998	19.28031
1999	18.71173
2000	18.11554
2001	17.234
2002	17.29055
2003	19.55874
2004	19.08468
2005	19.50026
2006	20.25215
2007	20.00486
2008	18.60193
2009	19.95317
2010	21.24005
2011	21.54691
2012	19.2727
2013	19.25248