Before revision:  In addition, we revisit the effects of fundamental price drivers, such as coal prices, gas prices and measures of economic activity, on allowance prices in the EU ETS using a time-varying coefficient regression model .
After revision:  In addition, we revisit the effects of fundamental price drivers, such as coal prices, gas prices and measures of economic activity, on allowance prices in the EU ETS using a time-varying non-parametrical regression model. Finally, we examine the two potential explanations from a theoretical angle to shed light on candidate underlying mechanisms. We conclude that no explanation can be ruled out, but further research is needed to increase confidence in either .