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In the different Stack Exchange reputation leagues, like this one below,

excerpt of 2015 math reputation league

there are nice $\color{green}{\text{+green}}$ or $\color{red}{\text{-red}}$ or $\color{grey}{\text{grey=0}}$ numbers called "change". What is the algorithm behind those figures?

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Those numbers are the "change in rank", determined by the difference between the rank from the previous $time_frame and the rank from the $time_frame being viewed (where $time_frame is either week, month, quarter or year).

So from the image, Mike Miller is ranked #161 in the viewed year (turns out to be 2015), and saw a change (in rank) of +20 from the previous year, meaning that he was ranked #181 in the previous year (2014).

Mike Miller reputation league 2014

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  • $\begingroup$ I just don't get that: 181-161=20, 7696-6622=1074. Where does 547 come from? $\endgroup$ – zoli Aug 9 '15 at 13:20
  • $\begingroup$ @zoli: That should be the difference between the 2014 rank and the 2013 rank (181+547=728). Actually, it's off by one, which is something I can't explain. $\endgroup$ – user642796 Aug 9 '15 at 13:27
  • $\begingroup$ I am still confused: I do not have a 2013 rank. I do have a 2014 rank, 8146. My current year rank is 157. The difference, 8146-147=7989. And my change is 7995. $\endgroup$ – zoli Aug 9 '15 at 13:41
  • $\begingroup$ @zoli Changes for the current $time_frame change could be the fault of caching. This is not a definitive answer, but something similar was reported on Meta Stack Exchange, which automagically fixed itself. Maybe users who have since been deleted caused this discrepancy? I'm really not certain. $\endgroup$ – user642796 Aug 9 '15 at 13:52
  • $\begingroup$ THX. THX. THX. THX. $\endgroup$ – zoli Aug 9 '15 at 13:54

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