Why different with Google's data on visitors

Why different with Google Analytics’s data on visitors?The piwik’s data is less than Google Analytics’s.

Hi can you see this thread and do as I asked in the last post. I realize you asked for visits but google is special in the way it captures visits and the PVs and UVs metrics are more critical and telling metrics i feel.

http://forum.piwik.org/read.php?2,98371

Do you know what is the difference between them? I would like to know why this difference caused.

Here is a link for a comparison of the 2 but bottom line both calculate things differently.

Something else GA depending on volumes does sampling of data and does not report everything in those cases.

As i mentioned previous look at the thread and if you want help i may be able to identufy some things that could surprise you.

Good Luck