Year	Number
1971	17.46079
1972	15.42143
1973	14.23736
1974	14.18128
1975	13.62824
1976	10.10037
1977	10.6195
1978	10.27938
1979	8.77359
1980	8.52122
1981	8.61636
1982	8.35457
1983	7.86524
1984	8.08459
1985	10.01162
1986	8.30274
1987	10.10766
1990	11.82828
1991	12.87154
1993	11.3019
1994	11.84452
2002	11.09684
2003	11.07543
2004	10.85278
2005	10.35915
2006	9.81226
2007	10.16743
2008	10.71457
2009	10.54274
2010	10.59304
2011	10.41057
2012	10.52573
2013	10.45601
2014	10.80291
2015	10.43427
2016	10.53152
2017	10.4633