Year	Number
1972	13.15
1973	17.25773
1974	18.11321
1975	15.30496
1976	13.47297
1981	18.46403
1982	18.41528
1983	18.89172
1984	18.95509
1985	19.51917
1986	23.0098
1987	25.24606
1988	25.425
1989	27.56037
1990	27.90244
1992	25.065
1993	24.65823
1994	20.36078
1996	18.88535
1999	22.81029
2002	31.85714
2006	31.29783
2007	34.25269
2009	29.71343
2011	27.89546
2012	26.55834
2013	25.13412
2014	24.54023
2015	22.77297
2016	23.75349
2017	22.727
2018	25.41709
2019	26.83286