Cpc or cost per click is the amount of money you are paid for each click that occurs on the adsense ads. Higher the cpc higher the earning per click. So publishers are always looking for ways to increase their cpc.
So what does cpc depend on. Simply put, it depends on the amount of money the advertiser is willing to pay for his ad displayed. One of the theories about adsense says that google tries to show the highest cpc ad to a given ad slot or something similar.
However in my experience I believe that for obvious reasons this cannot be possible. If google were to show the highest cpc ads all the time, then it would drain out the high paying advertiser before the low paying advertisers get a chance. So there must be some kind of rotation policy in the adsense engine that displays a mixture of cpc.
Low cpc ads
If the adsense inventory runs out of proper ads for your website, it will start showing backup ads. These ads may be totally irrelevant to the topic of your website and in most cases these are the ads that have very low cpc. This is common. Have you seen an ad of sun glasses on a website that teaches C programming, or an ad of toothbrush on a website that talks about servers and internet.
It happens that some advertisers try to buy any possible traffic for very cheap and from any kind of audience. There are terms like "made for adsense" websites etc. which are used for websites that just try to pull in traffic through adwords and then make the visitors click higher cpc ads on their own website to generate income. So they are commonly placed in backup ad situations. Or otherwise google runs of ads for a webpage, it might just display some nearest matching ad without any significant cpc.
Moreover its important to mention that Google had already clearly stated any any attempts to selectively block ads will unlikely cause any increase in earnings or cpc. The google adsense engine already works out the best level to find the most relevant ads for a webpage.
That is totally fine. Ofcourse google needs to do all it can to take of these things. However sometimes some "spam" or even "scam" kind of ads creep in due to some matching keywords on your website and can have a negative effect. So I just chose to review the ads once to make sure nothing like that was happening. This seemed to have an effect on binarytides. After blocking certain types of ads I noticed a slight improvement in the cpc.
The google adsense interface has 3 options to block ads
Block an ad by url
This option allows the publisher to block ads from particular urls. For example you might want to block ads from your competitors since you know their urls/domain names.
Block entire category
This will block an entire category like hotel industry, cosmetics etc. There are certain sensitive categories too. You may want to block those categories entirely that are far away from the nice of your website. However the google adsense engine takes care of showing relevant ads, so this is not necessary.
Block individual ad units/adword accounts - Ad Review center
Here you can check individual ads in their original sizes that appear on your website and inspect them. If you find any ad that does not make any sense or is totally useless, you can consider blocking them.
Find low paying ads
Estimating the cpc
I am not aware of any technique or method that can be used to find out the exact cpc of a certain ad url. This is more of a guess work with intuition and observation over a period of time. It begins at the "Ad Review Center". The ad review center is going to show all the ad units that had a significant amount of impressions on your site.
I recently checked the ad review center for the first time and started looking at what sorts of ads show up. As I kept browsing, I noticed that some ads appeared multiple times for different ad sizes, like once for 728*90 and again as 300*250. So I kept browsing. Most ads were related to the topic, and some were bit off-topic. It was easy to understand that whenever the adsense inventory ran out of "targetted" ads other kind of less relevant ads started showing up.
So this is all the information we have and we have to guess if there is some very low cpc ad out there.
When browsing through the ads I noticed some strange pattern. One particular ad (it was whatismyipaddress.com) had too many units in the review center (17 to be exact in just square shapes). Those included text, image and flash animations. It was appearing far more than any other ad. Now this ad was somewhat related to few posts on the blog due to some matching keywords, but there was no reason for it to have so heavy impressions. I also remembered that particular ad showing up too many times on binarytides. So I opened the url and checked it. And it was a very small site that was not selling any product or service, but just had a large advertisement to earn some money.
So this was a "SPAM SITE".
Now the main observations in this case were :
1. Very high impressions (because too many ad units of this url appeared in the ad review center). 2. The site itself did not seem to be selling something, like a product or service.
Block the ad
This led me to conclude that this advert is a fraud/spam/scam that was "by chance" filling the ad spaces on my website and spoiling my cpc. I blocked all units of that ad right away. The very next day I noticed a spike in my earnings. However I used to get spikes every 4-5 days and it was already time for it so I decided to observe for few more days.
The next day onward I again saw other units of the same ad url. I kept blocking them. In 3 days I had blocked all units of it. And then came some interesting results.
For the first time in my adsense history, the spikes continued for over a week making a higher average line in the earning graph. This was simply amazing. Take a look at what I am talking about
Note the graph from 17th novement onwards. The cpc kept high for many days continuously.
Some interesting observations
I also found that after blocking those bad ads, the next ads that came up were much more relevant and sensible to the content of the website.
Another important thing I noticed was that the $0.01 (1 cent) clicks vanished. Earlier they were very frequent and now they were totally gone. It was probably that spam site that was causing the $0.01 clicks.
So you may also want to review your ads in the ad review center and block any of them that appear to be fraudulent. I following some very basic ideas to detect spam ads.
1. Are they selling any real product/service ? Do they appear like a proper company ? 2. Are they themselves trying to earn from some adverts on their website 3. Do they have too many units in the ad review center.
Apart from these, I also blocked some other kinds of advertisements
1. ads asking for donation 2. ads that are totally irrelevant to my website topic (like factory equipment for example)
I am not very sure if this is a proper technique that is going to work for all. As far as adsense is concerned no effect can be strongly related to any particular optimisations. Experts would say that such kind of micro ad management is really not worth, since if a site is getting large and quality traffic, adsense engine would itself manage the ads in the best way.
Moreover Google mentions that users should not try to manage their ads too much by blocking them or changing their ad type (text/image or sizes) and that it is not going to help publishers earn more. This is mostly true since the adsense algorithm does all the analysis on a website, like keywords, quality etc to determine the best ads.
But from time to time, many have reported significant differences in their earnings based on certain optimisations. So I think its not a bad idea to try out new things on your adsense account.