# Trend shifts in timeseries

How can we detect trend shifts in time series? I know of Ets in R which tries to make trigonometric analysis of seasonal data. However I have not found yet a way of finding periodic trend shifts in time series. I feel the current methods cannot predict trend shifts. They can however guess the extrapolation of the current trend which is more of a localised prediction for trend. Pardon me if my question is not correct. Thanks in advance.

• No extrapolation method can $predict$ trend shifts. Only domain knowledge and judgement can predict future trend shift. And you are incorrect in saying that ets models use trigonometric analysis of seasonal data. – forecaster Jul 16 '15 at 19:54