Relative percentage increase / decrease

Hello, everyone. First time posting here. I am not a mathematician and I have only the most basic knowledge of statistics. But as luck would have it, I wish to calculate something that I'm not sure how to do. I can do without it, but I'd like to include this in my analysis.

My problem is as follows: I want to know if it's possible to calculate the percentage increase or decrease of B from one year to the next, relative to the overall increase or decrease of A, which B is a part of. For example, how would I calculate the percentage of increase / decrease of black cats born in 2020 and 2021, relative to the number of all cats born in 2020 and 2021?

If, for example 100 black cats were born in 2020 and a total number of cats in 2020 was 1000, and 200 black cats were born in 2021 out of the total of 500 cats in that year, what is the percentage increase of black cats relative to the population of total born cats? I assume that it's different (greater in this case) than just the simple increase without taking into consideration the total population of cats.

Also, same for decrease.

I've attached the excel file with concrete numbers that I need, but I'd really apreciate the formula so that I could calculate it myself.

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  • I actually suspected that it is useless and absurd, which is why I stated that I can do without this data. But since this is not my area of expertise I needed an opinion of someone who actually knows what they're talking about. Thanks.

  • Thank you for the tip and feedback :)

The answer is accepted.