Quote:
Originally posted by thewaitinggame
that's amazing  ty.
S&M's recent update got labeled "red" (gain of: +0.0119) BTW's however got "green" (gain of: +0.0121) & Best Love Song (gain of +0.0074). I assume if it was a comparison to ALL other tracks it would be a certain value that's the average gain or lose for the whole chart, no? |
The current algorithm is a bit difficult to explain but I will try.
I define the relative popularity of song A compared to song B as the popularity of song A divided by the popularity of song B.
What it does is for each song it calculates the relative popularity with all other songs, at the current time and at the previous time. Then it calculates the difference between these two relative popularities. So a negative difference means song A lost ground to song B, a positive difference means song A gained on song B. So for each song you have up to 99 of these differences (cause there are up to 99 other songs that have a known popularity at the previous time).
Then it takes the median of these differences, and if it's negative then it will be labeled red, if it's positive it will be labeled green. This way you will always have roughly half the chart as red and half the chart as green.
If you look at the percentage growth of the individual pop bars, then your example makes more sense. The absolute gain of S&M was 0.0119 but percentage wise it was a gain of 2.2%. Similarly, BTW went up 2.7% and Best Love Song 2.36%. So I think S&M was very close to being green as well.
Yes, It was barely top1000 @ iTunes, but same happened with Firework at the beggining, and we knew how the story ended 
