I've always wondered

Whenever a reported writes about the stock market, they always give the reason for movement in either direction. Today's AP for example:

Wall Street has ended a relatively calm day with a moderate decline, with the Dow Jones industrials falling about 76 points as profit-taking set in after Monday's massive advance. It's the first time in nine sessions that the Dow hasn't closed up or down in triple digits.

emphasis mine


To which I have always wondered... really? How do you know that exactly? Did you poll traders? What was the methodology?

I understand the all to human need to find a reason, but I've never seen evidence that this tendency doesn't use the Bureau of My Ass for it's statistical analysis.