Year	Number
1971	28.58095
1972	28.3359
1973	28.00313
1974	28.061
1975	28.5924
1976	29.01752
1977	30.87913
1978	30.66521
1980	32.14948
1981	32.19058
1982	31.14637
1983	31.56999
1984	30.97276
1985	30.721
1986	30.85887
1987	31.45627
1988	31.84201
1989	33.00045
1990	32.66715
1991	32.8906
1992	33.41975
1993	33.67088
1994	33.46948
1995	33.73656
1996	34.47076
1997	34.72563
1998	34.47868
1999	34.69483
2000	35.31923
2001	35.20686
2002	35.38941
2003	34.92513
2004	34.53153
2005	35.07377
2006	34.59417
2007	33.66837
2008	33.7418
2009	31.43572
2014	31.35082
2015	30.26629
2016	28.98824
2017	29.08352