An investor must comprehend a company's financial reports before investing in the company. It is easy to access the financial information of publicly traded companies in Taiwan through the official financial reports that are published every three months as required by regulation. This study calculates financial ratios and performs statistical analyses using data from a financial reports database, which is established by the Taiwan Economic Journal (TEJ). However, it is time-consuming and difficult to draw any conclusion by looking at all the financial ratios simultaneously. This article first standardizes data by using median and mean absolute deviations to eliminate company category differences as well as outlier influence. Then the generalized estimating equations model (GEE) is used to develop a practical selection rule (PSR). Only five ratios are incorporated into PSR: accounts receivable turnover ratio, equity ratio (debt ratio), asset turnover ratio, return on assets, and cash flow ratio. The prediction accuracy of PSR is validated and reaches as high as 0.822 (in terms of the traditional rate of accuracy, it reaches as high as 0.960). Thus the PSR can be used as a reliable investment tool.