Dear AV Community,
I am currently working on Exploratory Data Analysis of a Quarterly Data Set for a Time Series Forecasting problem. Based on the analysis I have done so far, I have come across a subset of data (~30% of data) whose overall trend is negative. Just to clarify, the variable of interest is depicting an overall negative trend for quarter “Q1” data over years 2013 to 2018. The variable of interest may or may not show the same overall negative trend for other quarters such as Q2, Q3 and Q4. For 50% of this subset of data, the overall trend is negative for all 4 quarters individually across years 2013 tp 2018 meaning trend is negative for Q4 across years 2013 to 2018 and likewise for other quarters.
For such a dataset that shows an overall negative trend over years, what type of Time Series Model should be used? Can you please make any suggestions on this problem.
Please write back if you need any additional information or have any questions about the dataset?