Year	Number
1984	3.33369736549514
1985	1.773722052730792
1986	2.0624519986020156
1987	1.3556251546567186
1988	1.1160997711729579
1989	1.0705506691657312
1990	1.3060651428917325
1991	1.3060537387528521
1992	1.504534955118108
1993	1.5356905444458648
1994	1.5766688906687403
1995	1.7423978925556114
1996	1.9707231816268889
1997	2.595188564977609
1998	2.8744262713757953
1999	2.84414831296105
2000	3.8538399766374853
2001	4.640340345900514
2002	3.6453514851118505
2003	2.619615080158548
2004	2.9925456766202942
2005	2.968183580798287
2006	2.7637199715656378
2007	2.9018364741051657
2008	2.427225978195618
2009	2.0972365944007785
2010	2.068618334707908
2011	2.027531776665043
2012	1.9759804472140932
2013	2.31829360675135
2014	2.318882103814377
2015	2.5436342806347083
2016	2.460258366009584
2017	2.4940628835577394