Advice on Adsense CPC rates or alternatives to Adsense

We would like advice on Adsense CPC rates We publish a site which gets around 250k page views per month. 9 months ago we made changes to ad positions and improved the click through rate. But that improvement has been countered by a drop in the CPC The data comparison from the last 30 days and the same 30 day period a year ago shows a CPC in the US dropping from £1.28 to £0. I am looking for advice on: Is this a common trend affecting the whole industry Is that any action we can take to get back to the CPC rates we were achieving 12 months ago Is there any other Ad serving service that would bring in more income than Adsense Attached is a PDF - page 1 is the last 30 days, page 2 the same period in 2012