Year	Number
1978	31.06642
1979	31.23032
1980	31.29402
1981	31.35406
1982	31.27451
1983	31.46123
1984	31.45513
1985	31.2872
1986	30.65816
1987	30.74625
1988	30.64399
1989	30.13131
1990	29.85744
1991	29.57144
1992	29.19093
1993	28.99024
1994	28.91272
1995	28.68717
1996	28.56183
1997	28.21811
1998	28.80902
1999	27.20033
2000	27.08789
2001	27.95144
2002	26.69572
2003	27.17367
2004	27.52195
2005	28.58852
2006	28.57687
2007	28.12136
2008	29.87886
2009	30.43249
2010	28.01385
2011	27.62268
2012	28.47869
2013	27.99108
2014	27.26742
2015	27.41033
2016	27.40284
2017	29.97227
2018	27.46162