Background
Performing multiple linear regression analysis on dataset containing 21 time-series of 4 data points. Each data points represents 9 variables.
R² adjusted is not decreasing rapidly after adding more variables.
Problem statement
Since the 4 data points are a static window of a longer time-series I am thinking autocorrelation between the data-points is the problem.
Question
How to visualize or estimate if there is autocorrelation inside the different time-series?
What I have tried:
I think ACF of the residuals is not working since I have 21 time-series.