Year	Number
1980	17.93413
1981	16.74747
1982	16.67187
1983	16.60881
1984	15.8555
1985	16.13265
1986	15.78476
1987	15.6636
1988	15.45324
1989	15.51227
1990	13.31749
1991	12.52821
1995	15.01711
1996	14.53263
1997	14.01797
1998	13.62151
1999	14.66174
2000	15.32815
2001	15.15422
2002	14.36776
2003	13.9797
2005	14.64833
2006	14.11456
2007	14.1662
2008	13.67053
2009	13.42271
2010	12.96228
2011	13.03218
2012	12.65309
2013	13.25139
2014	13.11067
2015	13.22948
2016	12.93654