Yesterday, I received an email from someone who’d purchased one of my ebooks. Her question was one I’ve been asked several times before: “How many instances of keywords within the copy are enough?” That’s like asking, “How long is a piece of string?” There isn’t one answer. Proponents of keyword density formulas will quickly spout out a percentage: 4%, 6%, 12%. However, I wonder where they get these figures from. [...]