Earnings reports for S&P 500 companies have continued to impress in 2005. Will the good times keep rolling in 2006? There’s reason to wonder, in part because interest rates are expected to rise further, and it’s not clear if the stock market will be able to shrug off the trend indefinitely. The United States economy faces other challenges as well, ranging from trade and budget deficits to next year’s arrival of a new and therefore untested Federal Reserve chairman as replacement for the retiring Alan Greenspan.