I have 2 variables, A and B, and 2 time periods, 1 and 2.

A1= 1
B1= 2

A2= 3
B2= 4

I want to analyze the differences between the ratios of both periods.

A1/B1= 0.50
A2/B2= 0.75

The ratio has increased by 0.25 from period 1 to period 2.

I want to show how much of the increase is due to A and how much of the increase is due to B. For example, I want the end result to be A=0.15, B=0.10 (I know that these numbers are wrong). How should I calculate this? Is this possible?

Thank you!