All opinions that rely on underlying facts, however, are not necessarily outside the opinion privilege. If you state the facts on which you are basing your opinion, and the opinion you state could be reasonably drawn from those truthful facts, you will be protected even if your opinion turns out to be incorrect. For example, if you were to say "In my opinion, Danielle is failing out of school" it would likely lead your readers to assume that there are some unstated facts you relied on to draw your conclusion. Such a statement would not be protected, as the privilege does not protect back door entry of facts as "opinion" through innuendo. On the other hand, if you state "In my opinion, Danielle is failing out of school because she is a blond and the only thing I ever see her do at the library is check Facebook," this provides the reader with the information you are basing the opinion on, and allows the reader to come to his own conclusion.
Compare the following two statements:
"During the last six months I've seen Carol in her backyard five times at around 1:30pm on a weekday seated in a deck chair with a beer in her hand. I think Carol must be an alcoholic."
"I think Carol must be an alcoholic."
The first example states true, non-defamatory facts upon which a reasonable conclusion (that Carol is an alcoholic) is based, and also emphasizes the limits of your knowledge (that you only saw Carol five times). It would be protected as a statement of opinion. Under the second example, readers would likely assume that there are unstated, defamatory facts upon which your conclusion is based. Therefore it would likely fall outside of the privilege.