Year	Number
1970	37.88876
1971	37.65384
1972	37.55241
1973	37.72809
1974	37.47169
1975	37.919
1976	37.85793
1977	38.23863
1978	37.02764
1979	36.86007
1980	37.42236
1981	37.18224
1982	37.15209
1983	36.65515
1984	36.63457
1985	36.85175
1986	36.8522
1987	37.23715
1988	36.92012
1989	35.59579
1990	36.93658
1991	37.04255
1992	36.65263
1993	36.44697
1994	37.27058
1995	37.71209
1996	36.54465
1997	38.89153
1998	39.93197
1999	40.12334
2000	40.65323
2001	40.04866
2002	41.11949
2003	40.19381
2004	40.79102
2005	40.70217
2006	40.65422
2007	41.42107
2008	41.07022
2009	40.48349
2010	39.70246
2011	38.56908
2012	40.02012
2013	36.61039
2014	35.77044
2015	35.34598
2016	35.41145
2017	35.40572
2018	35.41248