The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage. NEW YORK ( TheStreet) -- U.S. stocks rose last week by 2.1%, as measured by the S&P 500 Index, once again rebounding off the low end of the range from about 1100 to 1200 that has constrained the Index for the past couple of months. The rebound was driven by a combination of solid and better-than-expected economic data, few negative earnings pre-announcements, supportive actions by foreign central banks, and talk among European policymakers of injecting capital into Europe's banks to insulate them from a potential Greek default and recession. While macroeconomic factors are likely to remain key drivers of the market this week, microeconomics will also garner investors' attention as companies begin to release their third-quarter earnings reports. Four times a year investors focus on the most fundamental driver of investment performance: earnings. As you can see in chart 1, the performance of the S&P 500 and analysts' revisions to their earnings per share (EPS) estimates are closely linked. Market participants have priced declines in earnings into stock market valuations, as we detailed in the Weekly Market Commentary from Sept. 9 entitled Recession Obsession. Yet, analysts have high expectations for earnings. The consensus of analysts expects double-digit, 13% profit growth (compared to the third quarter of 2010) in the third quarter of 2011, as profits reach a new record high for the first time since the Great Recession, and 15% year-over-year growth for the fourth quarter for S&P 500 companies. Who is right? The truth is likely to be in the middle as earnings expectations are revised modestly lower and markets price in a less dire outlook for profits as results are reported and guidance on coming quarters is provided by corporate leaders. In recent weeks, third-quarter earnings estimates have been falling. Of the 127 companies that pre-announced third quarter earnings guidance in recent weeks, the ratio of negative-to-positive news was 2.6, worse than the average ratio of 2.3 since 1995. For S&P 500 companies that have reported third-quarter earnings so far, 21 of 29 (72%) have exceeded estimates, while six have missed estimates.