| Year | Value | | 2019 | 31.448848674036 | | 2018 | 32.533218502359 | | 2017 | 30.095113199618 | | 2016 | 29.005690069003 | | 2015 | 27.94312503793 | | 2014 | 26.937279736519 | | 2013 | 10.733283781495 | | 1999 | 85.554697916605 | | 1998 | 77.961679109972 | | 1997 | 69.421687059848 | | 1996 | 72.150009362609 | | 1995 | 82.629676356515 | | 1994 | 92.504154944828 | | 1993 | 73.287434489262 | | 1992 | 44.381173566704 | | 1991 | 50.885878764986 | | 1990 | 48.352956920881 |
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