I have a question about the interpretation of a decomposition plot. From Hyndman's book "Forecasting: Principles and Practice"
which results from a classical additive decomposition model of the data. If we closely look at the seasonal components, wee see that the value of the troughs slowly changes over the years. What does that mean ? That we have an evolving seasonal effect or that maybe a multiplicative decomposition would be more suitable in that case ?