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 26-Jun-2008, 23:24 #1 NRP Senior Member   Join Date: Aug 2004 Posts: 1,870 Percent Difference How is it calculated? % diff = (start-end)/start or (start-end)/end? It seems to me like the former equation should be used because the change should be relative to the starting point for the number to have any physical significance. However, some stuff on Google suggested that it should be calculated using the latter equation. Which way is correct, and why? If a mod feels this belongs in a different area please move.
 27-Jun-2008, 00:03 #2 AlStrong rwaaaraararagh   Join Date: Feb 2004 Location: beaver Posts: 14,047 I would have picked the former as a representation of what has changed since before -> it tells me improvements or detriments based on a known quantity. The latter represents what the past was like in relation to now which is well... I don't find it that useful. (This should probably be in GD) __________________
 28-Jun-2008, 15:04 #3 Xmas Off-season   Join Date: Feb 2002 Location: On the pursuit of happiness Posts: 3,019 Always (end - start) / start, so it's positive if end is more than start. Calculating relative to the end point really doesn't make much sense. __________________ Binary prefixes for bits and bytes
 28-Jun-2008, 16:05 #4 trinibwoy Meh   Join Date: Mar 2004 Location: New York Posts: 9,809 What he said ^ It's always relative to a starting point. __________________ What the deuce!?
 28-Jun-2008, 23:24 #5 Mintmaster Senior Member   Join Date: Mar 2002 Posts: 3,786 I'm going to have to disagree a bit with these opinions. The way percent change is calculated always depends on how you use it. Saying "heat output used to be 20% higher", "we started our plans when we had 30% more cash, but plans change", etc. all divide by the end amount. This is something that several video card reviewers need to learn as well. If you say card A is X percent faster or slower than card B, you have to divide by card B's score. Always divide by the reference point, i.e. what you're comparing a change to.
 28-Jun-2008, 23:36 #6 Anarchist4000 Member   Join Date: May 2004 Location: Somewhere, IN USA Posts: 313 Unless you're in a marketing field, then it's the way it's meant to be graphed.
29-Jun-2008, 03:09   #7
trinibwoy
Meh

Join Date: Mar 2004
Location: New York
Posts: 9,809

Quote:
 Originally Posted by Mintmaster I'm going to have to disagree a bit with these opinions.
You're not disagreeing though. You just changed terminology from "starting point" to "reference point". We're all saying the same thing.
__________________
What the deuce!?

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