*Excludes Observations that spanned multiple years

  B
b
t
W
w
 
Pre 197020017019
1970100304
1971000303
1972000000
1973000000
1974000202
1975000000
1976100001
1977000202
1978000101
1979000000
1980000000
1981000202
1982000000
1983000000
1984000202
1985000202
1986000101
1987000101
1988000101
1989000000
1990000000
1991000303
1992000000
1993000000
1994000101
1995000202
1996000000
1997000000
1998000000
1999000101
2000000101
2001000000
2002000000
2003000000
2004000000
2005000000
2006000000
2007000202
2008000000
2009000101
2010000000
2011000000
2012000000
2013000000
2014000000
2015000000
2016000000
2017000000
2018000000
Total40048052