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How to make percentage differences end up the same? So larger number changes are even with smaller number changes...examples:

(a) New Price: 126.953 Old Price: 126.83 Difference = 0.123 / 0.09%

(b) New Price: 26.953 Old Price: 26.83 Difference = 0.123 / 0.45%

Both of them have a difference of 0.12 but extremely difference percentage differences, how would I calculate it to be the same percentage difference?

Sven Kahn
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    percentage is always respect to some characteristic value. You have two scenarios which vary in magnitude. The question is why do you want the percentages be the same? lets scale up the examples $1\to 2$ and $100000000\to 100000000+1$ do you really want to see a percentage change to be the same for both cases? for stock prices one is a better bet than the other in terms of a returns, would you bet £1 to get £2 back or £100000000 to get £100000001 back? But if you really determined you could set some maximum difference say $0.5$ and take percentages for that i.e. $0.123/0.5$. – Chinny84 May 05 '15 at 15:07
  • I'm writing a script that doesn't really consider the potential return, it just looks at the difference of the old stock price compared to current stock price in %, and if it's greater or = to X%, it'll do something. Without getting the percentages to be the same, it'll need many different thresholds, i.e.; if stock is less than 15, the change in % can be X, but if stock price is over 100, the change in % can be XX, so it'd make my life a lot easier if I can just "normalize" the percentages to be the same, if that makes sense – Sven Kahn May 05 '15 at 15:13
  • Still doesn't really make much sense to me, but this is because I don't work in the finance sector(yet)!. But if that's the case I would look at getting a distribution of differences and choose some scaling (charteristic measurement) to which you can create your heuristic. I have a feeling that changes would be skewed by the level of the stock price. – Chinny84 May 05 '15 at 15:18
  • You put me in the right direction and I got it sorted out for the most part, thank you. I think you'll be brilliant in the finance sector. :) – Sven Kahn May 05 '15 at 17:51
  • Cheers pal. I need the vote of confidence ;)!! Just out of interest and without giving away too much what's your job role? – Chinny84 May 05 '15 at 19:18

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