I have a fundamental question regarding calculation of percentage error
In the graph below, there is a calculation about what percentage of population needs to be vaccinated in order to prevent a potential third wave of COVID19
So, the target is 7 %, and currently vaccinated percentage is 4 %. So, in my opinion the shortfall is 3 % from target. However, in the graph below it has been calculated as 41 % (4-7 / 7 )
So, my question is which is correct. 3 % or 41 %, and why ?
It is easier if we consider a real value problem.
Suppose that there is a price drop of 3D (D for dollar) of an item. How "big" is the saving?
If the original price is 7D and it has been cut down to 4D, the saving of 3D is quite "large" because we have only spent 4D for that item.
But, what if the item was 10007D originally, and the discounted price is 10004D. The saving is also 3D, provided that we have spent 10004D.
That is why we need to use the percentage change formula to make a relative comparison.