There are many factors at play you can't really answer that. High traffic sites, even with high paying ads, will have low CTR, whereas lower traffic sites with decent ads will have 3-5%. I would review things over if you exceed 5%. Though if you aren't doing anything wrong why worry about the CTR in the first place? It is what it is and you have very little control over it.
i find your CTR really depends on your overall layout: the design of the site (which includes the template) & maybe more importantly, the location of your ads. how many ads you have above the fold, and what you have detracting from people seeing your ads are factors as well. before i added a cost per lead function to my sites, i was experiencing a 6-8% CTR. then i wanted ppl to focus on the CPL ad unit, so naturally my AdSense CTR dropped to about 2-4%. But I am making more money, as the CPL leads pay much more than I lost in AdSense earnings...
Well, my question in other thread answered here. So there is absolutely something wrong with my website with just 0.3% CTR . Maybe because people visit my website through image in my article so that they don't click the ads ? (for some keywords, some images in my article appear in 1 page of google search) Although all my article are absolutely unique and has more than 500 words each. Maybe just as Rupam said in other threads, I need to learn and learn again...
Yes, image source for traffic yields a VERY LOW CTR. My business partner had some images that he optimized and with a frame breaker was able to get a ton of traffic to his site. The problem is that those people are NOT looking for content, but rather just the image itself. Therefore, they are likely not interested in anything related to your ads. You need search traffic for your articles...
Good quality content + a nice CTR Theme could do wonders! Have you tried "Adsense Pro Ultimate"? I have been using for quite some time with great success, with CTR as much as 6-7%...
You Need to Think about user end and try to go through in depth. After considering and research about it make useful content and related ad that can increase your CTR .rate from your blog or web traffic... Like to increase more traffic consider www.webtrafficgeeks.com
That's just some crap he copied from wikipedia, nothing to do with adsense at all: http://en.wikipedia.org/wiki/Click-through_rate