I would like to ask a question about FLAC Compression, whether some of you know how it exactly works. Without naming the track, I have the same Single's US and UK version. Ripping the same track from both CD's in FLAC LEVEL 8 I get this:

US Version:
Average bitrate: 944 kbps
Compression Ratio: 66%

UK Version:
Average bitrate: 909 kbps
Compression Ratio: 64%


Not that it matters a lot, I'm just being curious. I woulda think I should get the same result, and yet, I don't. Why?

Edit:
Some additional infos:
- both version released in the same year
- i used the same programme for ripping

FLAC is a lossless codec, meaning that it uses special (and complex) mathematical algorithms to render a waveform exactly the same as the original by finding simple and/or repetetive segments of data and shortening them (kind of like how a journalist can use shorthand to write a sentence quickly and accurately by replacing common words with symbols). The more complex the original data, the less effective the data reduction is.

So, if a song has different versions, various nuances in the file's complexity means that the compression results will be different to each other.