Paid And Organic Search

"You rank #1 organically for your brand keyword search, and you’re trying to determine if and how much you are willing to pay for a paid ad on your brand keyword search. The goal then is to understand how the clickthrough rate (CTR) of the organic listing is affected by the presence of the paid ad. You’ll do this by looking at how the CTR of the organic listing changes with and without the presence of the paid ad. The CTR rates I am referring to need to be normalized for search volume. I’ll explain what that means below, but that was the tricky part that I didn’t get before, the elusive reality about which Matthias enlightened me."

Paid And Organic Search: Understanding The Math (And The Truth)