Year Percent change (Units) 1999 8.123 2000 3.204 2001 19.313 2002 11.095 2003 5.037 2004 7.524 2005 7.000 2006 11.911 2007 11.659 2008 9.388 2009 9.708 2010 6.618 2011 11.449 2012 7.709 2013 8.494 2014 7.661 2015 8.039 2016 12.518 2017 13.894 2018 28.525 2019 20.251 2020 13.122 2021 5.459 2022 9.185 2023 10.015 2024 5.431 2025 5.566 2026 5.006 2027 4.910 2028 4.852 2029 4.816