2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | Pooled data | |
n | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 900 |
| 2.62 | 2.47 | 2.62 | 2.62 | 2.83 | 3.16 | 2.63 | 2.63 | 2.39 | 2.64 |
S.E. | 0.2624 | 0.2471 | 0.2621 | 0.262 | 0.2833 | 0.3163 | 0.2632 | 0.2628 | 0.239 | 0.0883 |