On the other hand, loosely selective scans often return more than 10 percent of the original population. Useful scans tend to be fairly selective, but will rarely return an empty result list. Scans are designed to find stocks that are in a specific technical situation. If a scan is supposed to return stocks that have recently made strong upward moves, but most of the stocks it returns have not done so, then the scan should probably be refined until it is more accurate. Scans are designed with a particular investing philosophy in mind.
Value investors use scans that try to find weak stocks that are showing signs of a turnaround.
Growth investors use scans that try to find stocks that have recently moved higher on strong volume. And so on. Philosophic Accuracy refers to a scan's ability to find stocks that meet the designer's investing philosophy. This is probably the most important factor for evaluating a scan but unfortunately, it is also the hardest to measure objectively. A scan that one investor finds valuable may seem like a waste of time to another.