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create crosstabs (pivot tables) TARGET vs. ATTRIBUTES and compare them between periods. Crosstabs tell you how much has distribution & effect changed.
If you have continuous variables, start with binning into 5 bins on training data. Then bin new data with the same boundaries. And only then compare crosstabs.
Assuming no inter-dependency among the independent variables, checkout the correlations between target and each characteristic in both earlier time frame and current time frame. The variables that have drastic change in correlation over both the time frames could be contributing the most to the shift in target. For a more degree of accuracy, avoid correlations and draw scatter plots in both the time frames and compare the trends.
If your target is binary, plot the event rates for each attribute of all characteristics and compare the plots in both the time frames.
Hope this helps!