While we’ve heard in the past that Twitter can be a killer box office predictor, the same might not be true for social media and television ratings.

Social media monitoring company Viralheat spent a month tracking social media mentions — a million of them, in fact — right around the time that nine major TV shows were airing their season finales. The company looked at data from Twitter,Facebook, YouTube, Google Buzz and other sources, including the sentiment of all these mentions, comments and updates.

Then Viralheat compared the social media buzz with the Nielsen TV ratings for each show. Does chatter on the web equate to eyeballs on TV screens?

Not necessarily. Their research determined:

• Online buzz does not always correlate with ratings.
• Sentiment analysis of social media chatter casts those mentions in a new light.
• Even when ratings are lukewarm (as was the case for the Lost season finale) social media chatter can be overwhelming in volume. But a lot of those mentions online expressed a negative sentiment.
• Some shows, including Dancing With The Stars, saw good TV ratings but not many mentions online.

All in all, Viralheat found that Nielsen ratings combined with social media sentiment analysis provided the best snapshot of how a show’s season finale performed with viewers.

So, for you would-be social media gurus, next time you’re trying to measure a brand’s impact on the social web, remember to include some sentiment analysis along with your headcount, or you could be missing out on some critical information.

Here’s the infographic with more interesting factoids than you can shake a stick at; click to see the full version.