DOCTORS DON'T send you for a full-body scan every time you need a physical. They start with the basics--they take your temperature, listen to your heart and measure your blood pressure. Likewise, when you evaluate a stock, begin by conducting some simple tests on the financial figures to diagnose the general health and well-being of the company. In some instances, you'll want to probe more deeply. This article will help you use both simple and sophisticated tools to analyze stocks. The box on page 21, moreover, can help you avoid companies that practice overly aggressive accounting.

Before you begin a financial physical, you need to collect the data. Most of the numbers ...