The resident scientist to the search engine optimization community, Orion (Dr. E. Garcia), wrote a new short article named Overlapping Patterns: EF-Ratios, Separators, Patterns and Pitfalls; "Overlapping patterns within overlapping patterns! It takes few seconds to realize that query mode implementations can exhibit a fractal component."
In this article, he reviews the concepts of his creation, "EF Ratios", discusses Separators (spaces, delimiters, or stopwords) & EXACT queries (""), and Patterns & Overlapping Regions. But most importantly he explains why some of the "pitfalls SEMs/ SEOs should avoid" in terms of using keyword research tools. I'll quote the last paragraph here:
Ultimately, metrics based on search results are not just affected by tokenization and similar procedures taking place at the level of the individual IR architectures. They can be the result of relevancy scores assigned by the queried system. Combining these metrics with metrics from other search engines that account, let say, for user's query behaviors (i.e., search volume) to come up with a new metric is a highly questionable approach. SEOs, SEMs and keyword research firms should stay away from such practices.