Global Paid Search Spend growth - size, research etc

Looking for data and research on the size growth of the Global Paid Search

[clayduck]

Hi all

Can anyone point me towards data and research which maps out the growth of Global Paid Search spend over the last 5-7 years.

I have tried the usual sources - Jupiter, Forrester, Comscore but not much luck.

The research tends to be mainly region based e.g. US or Europe only.

All tips appreciated.

PS - Mods- posted this in Google Finance as its the most likely to get noticed and of interested to a wider group.