I’ve been looking into this over the past few months each time we have a new client who wishes to use our SEO services. I usually make a rough comparison of what they would be paying to get a certain number of clicks for certain keywords via PPC compared to what SEO costs and the benefits they can reap from SEO. Although it has been proven that PPC often has a higher conversion rate, SEO has the greater ROI in the long-run for long-term projects.
YOUMoz and Searchlight Digital have looked into the click-through rate of organic search results recently, giving more insight into how we can judge the value of search engine rankings. From my experience, I have noticed major difference between industries when it comes to CTR. There is a big difference between going shopping online via search engines and looking up the meaning of a word.