Year | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 |
Synergy degree | −0.0985 | 0.1504 | 0.1723 | 0.1999 | 0.2018 | 0.2772 | 0.3204 | 0.3487 |