|Anyone notice that Google is Paying Less over the Last Year?|
For instance, about a year ago, I was getting paid about $20 a day, with a ctr of 2%. Today, I've increased my ctr to 3.7%, and the same traffic brings in $20 a day. Does that make any sense?
Visitors to your site may only be worth $20.00 a day so G is adjusting payment as you adjust placement. Unless your content is completely unchanged, and even then it has changed, it has become more "stale"... too many variables to even try to figure out the problem with only the info you provided.
You increased your CTR?
You say that your CTR has increased during that time, but have conversions for advertisers increased at the same rate?
Many AdSense publishers optimize for clickthrough rates (e.g., by extreme "blending," placing several ads above the fold, using AdSense in lefthand navigation bars, etc.), but such optimization doesn't necessarily benefit advertisers--which means the publishers may be "smartpriced" or advertisers may add the non-performing publishers' domains to their blocking filters.
CTR, eCPM, and total $ are up for me year after year. But I'm constantly developing my sites and bringing new stuff online, as well as testing new ad layouts etc. All original (and reasonably high-quality) content, too.
Hard to compare one site (or group of sites) to any other, too many variables.
Think of driving down the highway where billboard ads might be placed. The town at the end of the highway says you can have only one billboard every five miles and they get x dollars for that space.
Now a businessman becomes the mayor and pushes through a rule that says you can have a billboard every 10 feet. As the billboards go up it is likely that the cost for that space will go down. Eventually they might even get blank billboards or, can you believe, ads for dating services and 'free widgets'.