| Year | Value | | 2022 | 31.647009185989 | | 2021 | 34.945909261741 | | 2020 | 37.54885233354 | | 2019 | 34.619416252979 | | 2018 | 32.71161032266 | | 2017 | 30.366154570783 | | 2016 | 27.977793630646 | | 2015 | 21.473157999939 | | 2014 | 22.869996879491 | | 2013 | 35.529001264654 | | 2012 | 36.687007820303 | | 1998 | 17.787811687206 | | 1997 | 10.824492498504 | | 1996 | 18.547648928207 | | 1995 | 16.469739608551 | | 1994 | 43.163744564975 | | 1993 | 7.5296135517332 | | 1992 | 14.913435045594 | | 1991 | 17.199601963988 | | 1990 | 6.5877212686481 | | 1989 | 13.792861007264 | | 1988 | 15.70171429411 | | 1987 | 10.816813085238 | | 1986 | 8.7453489865634 | | 1985 | 12.483063815514 | | 1984 | 0.70429332416194 | | 1983 | -5.4511017988378 | | 1982 | -9.0723727981015 | | 1981 | 2.483595177574 | | 1980 | -1.0424573493451 | | 1979 | -4.5837770647486 | | 1978 | 1.3641591795322 | | 1977 | -8.2732469900838 | | 1976 | -5.3203747518508 | | 1975 | 5.3764241649181 |
|