eCPM is the simple calculation of how much you earn /1000 page views (or projected amount if you have received less than 1000 page views, given your earnings so far). This number is entirely dependent on the price of the clicks clicked upon (and, of course, the number of clicks).

Alos, the current day's stats are not always up to date and should be taken will less than a grain of salt.

I actually know what eCPM is.

From AS: "For example, if a publisher earned $180 from 45,000 impressions, the eCPM would equal $180/45, or $4.00."

My sites:

Before: More money/same impressions = more eCPM

Now: Less money/same impressions = lower eCPM

For me, there is to much coincidence that one day is at $2 and the other day is at $5, with the same company ads running in my sites. My question again is:

Does AS decides what eCPM is giving to us in a daily basis? Does AD tries to compensate bad days by raising the eCPM?

Advertisers have a say in how much the click is worth, and ultimately what your eCPM is.

Add to that the unpredictable reasons for which visitors are coming to your site and their propensity to click or not click an ad, including whether they are shoppers, in debt, have a bad mortgage, their business is slowing down, are looking for info not products, etc. and you have a recipe for unstable earnings.

It's not just Google flipping switches from Mountain View. Many other factors influencing the eCPM. ;)

Before: More money/same impressions = more eCPM
Now: Less money/same impressions = lower eCPM

You're forgetting a key, if indirect, factor of the equation: clicks.
If you have the same number of impressions, but fewer clicks leading to less money, then blame your visitors for not clicking more.

If you have the same number of (or more) clicks with lower revenue, then most likely you can blame the advertisers for lowering their bids. Or fewer avertisers using the Content network. Or more advertisers blocking their ads from showing on your site. But like MB said, Google isn't flipping switches to raise/lower your eCPM.

The question I ask back is, WHY would Google compensate for bad days by giving you a good day? They don't owe you a stable eCPM or stable earnings.

Over the years, my eCPM has been heavily influenced by gradual changes in both the CTR for my site and the average click value I've been receiving. As far as I can tell, Google isn't controlling either of those, with the possible exception of click value, which can go up and down due to "smart pricing."

But like MB said, Google isn't flipping switches to raise/lower your eCPM.

Sounds good enough.

I just wanted to know if any one else tought the same way. It just seems odd the big change from one day to another.

WHY would Google compensate for bad days by giving you a goodday?

Believe it or not, I think that we are all important to Google, thus they want to keep us happy. If Google start losing us, and we all move to Yahoo, I think we can make a difference.

So you're not happy with the AVERAGE you're seeing? I have good days and bad days too, and yet the average makes me very happy. I don't need a bonus to keep me happy--and I don't think Google hands them out.

puckparches,

your question - "does AS decide what eCPM is giving to us in a daily basis?" - is very valid.

I have been analyzing my data set with a statistically relevant number of single values for about three years now. One thing that strikes me is that eCPM on a daily basis is volatile, while the long-term averages are not volatile at all.

This follows a certain pattern - eCPM goes up and then suddenly, usually after a week, drops between $0.50 and $0.75. It stays at this reduced value until it sharply goes up again.

It amazing that -despite these sharp rises and falls- the long-term averages seem to be "on track", like a straight line (pointing down).

Why should Google be doing this?

First, to line their own pockets. Second, to present an incentive for publishers to create more page views and clicks to compensate for the reduced income. Those who can not keep up with this growth requirement will fall behind and receive just Pennies in the future (because they are not as important to Google as those who actually can satisfy their demand for growth).

My sites, folks, my sites!

There is the other option to keep your earnings up...

Build pages that are more Search Engine Optimized and higher in the natural search rankings. Thus you don't need to keep building more and more crappy pages just to keep up.

Mike