A stock screener is designed to review all the quantitative points that come with a stock. Any number that you want to review in a stock will be revealed or analyzed in the screener. This is convenient, but it is not necessarily going to be thorough. The problem with a stock is that you need to look into both the numbers and outside factors to get an idea of what is right for your investment. A stock screener only works with the numbers. You need to do additional research on the stock to see what news stories or other points might have caused the stock to reach a certain total. In other words, the stock screener is just a simple program that makes it a little easier for you to find a stock that you can do further research.