Year	Number
1971	45.90793
1972	46.63227
1974	44.15724
1975	45.44791
1976	44.78182
1977	44.22086
1978	43.89227
1981	39.08709
1982	37.41357
1983	36.6442
1984	35.92316
1985	34.79416
1986	33.62718
1987	32.81685
1988	31.88843
1989	31.31406
1990	31.06703
1991	30.5361
1992	30.01775
1993	29.64061
1994	29.14454
1995	28.70808
1996	28.3372
1997	27.90964
1998	27.56511
1999	27.22577
2000	27.15793
2001	26.98308
2002	26.87027
2003	26.66029
2004	28.47157
2005	28.3176
2006	28.00397
2007	27.99039
2008	28.02416
2009	28.11672
2010	28.14672
2011	28.11199
2012	28.01636
2013	27.69096
2014	27.40876
2015	26.92701
2016	26.74201
2017	26.55228