The "rolling effect" most noticeably takes place in big radio releases on the 8th day of their airplay release, however if songs receive radio deals spanning longer than 1 day, or receive massive updates throughout the week, it could be seen in the 9th to 14th update too
When a song that has a lot of hype, or a radio deal, is release to radio on its first day, it garners a large amount of A.I, or Audience impressions. This simply means the amount of people who have heard the song. Each radio station gives a different amount of A.I, depending on location, format, and time of the day of the spin.
So, a song like Ke$ha's will get large support from a lot of stations in prime spinning times, thus a large first day, and sometimes 2nd to 7th day, A.I accumulation.
However, on the 8th day, the first day of the second week, the A.I will almost always drop, and by a large amount, for these songs due to the "rolling effect". Essentially, the amount of spins are compared to the same day last week, the 1st day in the case of the 8th day, and thus a change of spins and A.I is deduced.
So, for day 1, "Die young" was played by major stations on the top of every hour during the day, and by a lot of otehr stations a lot during the day as well. This is due to hype and it being a new release. Due to this, a massive amount of A.I was formed for the song.
On the 8th day however, the hype had dulled down and
normal radio rotations have been implemented, meaning an average amount of spins in average time slots. This reduces the A.I for that day, and with comparing to the 1st day, a large decrease can be seen, giving the impression to people that it's dropping a lot, when it's just coming down from a high to a normalised program.
A basic example:
Monday: 15M A.I (+15M) (Total 15M)
Tuesday: 5M A.I (+5M) (Total 20M)
Wednesday: 5M A.I (+5M) (Total 25M)
Thursday: 5M A.I (+5M) (Total 30M)
Friday: 5M A.I (+5M) (Total 35M)
Saturday: 5M A.I (+5M) (Total 40M)
Sunday: 5M A.I (+5M) (Total 45M)
A massive first week due to lost of hype. However, in the second week, it returns to normal:
Monday: 6M A.I (-9M) (Total 36M)
Tuesday: 6M A.I (+1M) (Total 37M)
Wednesday: 6M A.I (+1M) (Total 38M)
Thursday: 7M A.I (+2M) (Total 40M)
Friday: 7M A.I (+2M) (Total 42M)
Saturday: 7M A.I (+2M) (Total 44M)
Sunday: 8M A.I (+3M) (Total 47M)
As you can see, each day is compared to the amount of A.I received on
the same day last week, and thus a large negative update is shown.
I hope that makes sense. It's long and messy, but I did it quickly.
