Since the end of April, beginning of May I experienced a sharp decrease in CTR even though my traffic is up 35% and as a result i'm earning 25% less than I was prior to May. I use OpenX to manage advertising on my site, so today i checked it for the first time in a couple of months. I found that from around May 1st it was consistently reporting ~250 clicks more than what adsense was reporting. Today adsense tells me I have 650 clicks so far, but OpenX says 920. This can't be: -a OpenX error - because prior to May 1st the differences were never more than ~20. -invalid clicks - because invalid clicks are reported in adsense, but they pay $0. This is a well established site with 3 million page views per month. There are alot of returning visitors so my CTR never really breaks 2%. Anyone else experiencing this? OpenX has free hosted version if you want to test this out. Some wordpress plugins can do tracking too. I'm sure I'm not the only one.