Year % 1990 18.1818181818182 1991 20 1992 21.0526315789474 1993 24 1994 21.875 1995 24.390243902439 1996 25 1997 24.2424242424242 1998 25.3012048192771 1999 25 2000 25.5813953488372 2001 25.7861635220126 2002 25.6410256410256 2003 26.271186440678 2004 26.3698630136986 2005 26.685393258427 2006 27.2300469483568 2007 27.2908366533864 2008 27.4914089347079 2009 27.5187969924812 2010 27.5769745649264 2011 27.6029055690073 2012 27.5862068965517 2013 27.6464542651593 2014 27.7511961722488 2015 27.7628032345014 2016 27.9050042408821 2017 27.8807413376309 2018 27.9320987654321 2019 28.1133482475764 2020 28.3333333333333 2021 28.5613540197461 2022 28.7972508591065