| Year | Simple Mean | Median Method | Jackknife Method |
| 1986 | −0.76 | −0.77 | −0.79 |
| 1987 | 0.27 | 0.26 | 0.28 |
| 1988 | −0.12 | −0.13 | −0.13 |
| 1989 | −0.55 | −0.56 | −0.57 |
| 1990 | 0.01 | 0 | 0.01 |
| 1991 | −0.11 | −0.12 | −0.12 |
| 1992 | −0.29 | −0.3 | −0.3 |
| 1993 | −0.41 | −0.42 | −0.43 |
| 1994 | −0.58 | −0.59 | −0.6 |
| 1995 | −0.76 | −0.77 | −0.79 |
| 1996 | 0.03 | 0.02 | 0.03 |
| 1997 | −0.12 | −0.13 | −0.13 |
| 1998 | 0.56 | 0.55 | 0.58 |
| 1999 | −0.02 | −0.03 | −0.02 |
| 2000 | 0.23 | 0.22 | 0.24 |
| 2001 | 0.25 | 0.24 | 0.26 |
| 2002 | 0.16 | 0.15 | 0.16 |
| 2003 | 0.36 | 0.35 | 0.37 |
| 2004 | 0.01 | 0 | 0.01 |
| 2005 | 0.35 | 0.34 | 0.36 |
| 2006 | 0.35 | 0.34 | 0.36 |
| 2007 | −0.13 | −0.14 | −0.14 |
| 2008 | 0.3 | 0.29 | 0.31 |
| 2009 | 0.5 | 0.49 | 0.52 |
| 2010 | 0.96 | 0.95 | 0.99 |
| 2011 | 0.13 | 0.12 | 0.13 |
| 2012 | −0.15 | −0.16 | −0.16 |
| 2013 | 0.05 | 0.04 | 0.05 |
| 2014 | −0.3 | −0.31 | −0.31 |
| 2015 | −0.16 | −0.17 | −0.17 |