I don't understand if quality score is per keyword or per campaign or even per my domain name? In statistics it shows like per keyword, but I have some keywords which have just few impressions and one click (high CTR), but got disabled. It make me think that there are 2 quality scores one for campaing (domain) another for keyword and quality score which they show in statistics is a combined quality score. Is it right?
Its all of the above. All factors, it seems, have something to do quality score. But it seems to be the best kept secret on the internet. Your right that CTR has something to do with it, as well as bid, ad text, domain relevance, etc... If I knew exactly what it was, I'd be working at Google.
Hey, its the quality score formula... I guess you don't have to work at Google to get it. https://adwords.google.com/support/bin/answer.py?answer=10215&query=quality+score&topic=&type=f
Quality Score relates to the ad itself only and the factors in it: the ad copy, the landing page relevance etc