Originally Posted by Andy

In certain respects, he's correct that it's the media that can trigger stock market moves. Most of the trading today is done by computers and one of the inputs they use is newsfeed. They react off of key words in the news, causing the automated programs to either buy or sell.

I read an interesting study a couple of years ago about a program trading off of Twitter sentiment. It would categorize twitter posts as either positive or negative and then trade based on that sentiment.