Year	Number
1970	23.73598
1984	19.94021
1985	18.13333
1986	17.00501
1990	17.72716
1991	16.92352
1998	9.74394
1999	14.62227
2000	14.62638
2001	13.83643
2002	14.39427
2007	14.84725
2008	14.82472
2009	14.96024
2010	14.88117
2011	14.56807
2013	13.29749
2014	13.40591
2015	14.5488