CTR tanks. Why?

Let's list possible reasons and solutions.

[sven1977]

Let's assume one is in the following desastrous situation.
The CTR suddenly tanks by about half. What could be the possible reasons for this?

1) Terrible targeting: Have lots of experience with this problem. In the beginning, I could regularly observe how closely tied CTR and ad targetting are. Let's assume we fixed that problem and our ads are neatly targetted. But your CTR is still half of what it usually is.

2) MFA ads all over the place: Well, one could call that bad targetting, too. But let's assume that these MFA advertisers are actually in the same niche as I and thus: well targetted. Solution: Filter, filter, filter.
Let's then assume that your CTR (after you wait nicely for about a week until the last dumb MFA disappeared from your pages) is still rock bottom.

3) What now? What could be further possible causes? Ok, ok I admit, it's me who has this problem. And I'm begging for your input.
Some more ideas I had were:
- users were so disgusted from the MFA's (which I filtered now) that they don't want to click anymore in general.
- the current advertisers (even though non-MFA's and targetted) just have bad ads. Right! Their ads suck. We don't see it. But our visitors do sort of unconciously know that they don't wanna click them: Ads too boring, or whatever.
- the nature of my traffic suddenly changed (more SE traffic or more inbound-link traffic)

Maybe you can help me and many other users of this forum to dig for the solution of this probably common problem. Thanks a bunch. Your little brainstorm would help me out of my momentary crisis.
Sven

[G_Smitty]

Could it be that your website receives many repeat visitors who find exactly what they want on your site? Could it be because your a well established non MFA site and the end of the line? Or it could be that your users are ad blind. Have you tried rotating ad schemes?

[sven1977]

G_Smitty, thanks for your reply. Those are all possible reasons, but the main question is, why does it happen now (low CTR) and not earlier?
My site is online since July 2005 and I never had a problem with such a low CTR.

[pmidds]

Have you seen a change in where your traffic has originated from?

[sven1977]

Yes, I did. I'm getting more google traffic now. My top traffic-source is still non-SE though.
I do know that google traffic is less likely to click ads. I still don't understand why that is the case?

[pmidds]

Although I've never noticed it myself I have heard it say that Googlers are less likely to click ads than say MSNers. (edit: sorry didn't read your post properly- you already know this)

The reason given is that some google referels will be about as off target as they come. Just looking at the huge numbers that Google deal with suggests they will throw a higher number of unrelated traffic your way. Check what keywords are bringing them to your site.

If nothing has changed on your site (colours, content ad placement) the only variable that I can think of is the make up of your traffic.