Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.
U.S. stock markets have declined slightly today on very little economic news. Investors are still concerned about tapering from the Federal Reserve in coming months and, after a run-up nearly all year, it's pretty normal for stocks to take a bit of a breather. The Dow Jones Industrial Average (^DJI 1.56%) is down 0.46% late in the trading day and the S&P 500 (^GSPC 1.52%) has fallen 0.32%.
The up and down trading days of Alcoa (AA +0.00%) and Caterpillar (CAT 1.00%) continued today with the stocks climbing 3.2% and 0.8%, respectively. Investors are buying both stocks because of a report showing that China's industrial production rose 9.7% in July from a year ago. This follows positive data about exports yesterday and gives investors hope that China's economy won't slow as many have predicted. For the long term, we should be more concerned about the profits of both companies than about one economic report and the overall lower trends of the past year. 
AA Net Income Quarterly data by YCharts
We should also keep in mind that China can be notoriously uneven and inaccurate with economic reports, so buying on a single data point isn't a good move. Instead, look for progress on an earnings front and take heed of management's comments in coming quarters because that's more important for the stock long term.
AT&T (T +0.68%) continues to decline today, falling 1.3%. There's a lot of concern that T-Mobile will take share after gaining 1.1 million customers in the most recent quarter. The quarter may show that AT&T and Verizon Wireless need to be more flexible in pricing and contracts or risk losing customers to their smaller rivals. With the stock trading at 13 times forward estimates and paying a 5% dividend yield, I don't think there's any long-term concern for AT&T and dips like this are great buying opportunities for investors.
