When people think of stock screening, they usually think of sequential stock screening - that is they think of taking the stock universe and narrowing it down by applying filters one after the other until a final list of stocks that each meet the criteria is obtained.
Sequential Stock Screening is Binary
One key point is that sequential stock screening is binary - this means that at each point on the screen, the stocks in the stock universe (or the remaining stock universe) either continue or don't continue. Unlike simultaneous stock screening -- which screens stocks simultaneously based on a z-score -- sequential stock screening either keeps a stock in or tosses is out at each junction.
This binary nature of sequential stock screening is considered a weakness by some because a stock may be disqualified early on that would otherwise prove to be excellent given the overall screen (given the upcoming filters that will occur on the screen).
Initial Investment Universe - The Starting Point of a Stock Screen
The starting point of a stock screen is the initial investment universe - this is simply the totality of stocks that will enter the filtering system. Usually, an investment universe is comprised of publicly traded equities on the NYSE and the NASDAQ.
It is possible to include stocks that aren't traded on exchanges, but this isn't recommended for new investors or those new to stock screening as this can add complexity and can hinder liquidity.
Screen Criteria - What to Look At
You can literally look at almost anything in a stock screen - there really is not set requirement. Things such as
can all be looked at in stock screens. There are many stock screening strategies out there but they are beyond the scope of the current discussion.
Some Free Online Stock Screeners
Here are a few popular free online stock screeners: