Quote:
Originally posted by JakeKills
Wtf is the rolling effect? [/idiot]
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It's like the radio rolling effect if you've ever been in the Mediabase thread.
Basically, there is about a 24-hour rolling window for iTunes sales. When Taylor's song was released, it was instantly selling faster than every other song on iTunes, but in order to surpass the #1 song, it had to essentially pass the entire 24-hour sales of the number one song.
This took the song about 50 minutes. From that point on, since all sales were part of its initial rolling window, you saw everyone else's percentages decrease continually. Now that 24 hours have passed, you will see her start to drop in relation to everyone else because the initial rolling window has passed and now her sales rate is compared to her sales rate 24 hours prior (and it is not selling as fast as it was immediately upon release).
It's easier to think about in terms of radio airplay.
For the first seven days (the one week rolling window for airplay), assume a song gets heard by 2.5M people each day. Its updates would like this:
DAY 1: 2.500
DAY 2: 5.000 (+2.500)
DAY 3: 7.500 (+2.500)
DAY 4: 10.00 (+2.500)
DAY 5: 12.50 (+2.500)
DAY 6: 15.00 (+2.500)
DAY 7: 17.50 (+2.500)
At this point, the initial window is over, and rolling will begin. Let's assume on day 8 that the song is heard by a total of 2.8M people. Now, its update is taken in relation to the same period of the last rolling window:
DAY 8: 17.80 (+.3000)
since 2.8M (day 8) - 2.5M (day 1) = .3M
When you're in the initial window, you can only go up, but after that, you're getting compared to yourself.
Digital Sales Data: 2012/08/14
