Year % 2011 8.0054221465425 2012 6.18702858460746 2013 6.56102257085237 2014 6.18389010006754 2015 5.7247265660517 2016 5.71072482772314 2017 5.24619092380409 2018 4.74201086025218 2019 5.16828540729108 2020 4.77446925869926 2021 4.76216005308376