Matthew Hurst over at Data Mining has in interesting post about influence and authority. He correctly points out that they are not the same thing.
However, I think influence actually needs to go beyond number of readers. In the truest sense of the word, influence implies changing others’ opinions. So you could have a really polemic blog or blog posting that lots of people read, but doesn’t change those readers’ minds. Is it influential? Maybe, maybe not.
Not sure how you’d measure it, but you need to take the change your post or opinion has on others to really indicate influence.
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