Match Quality categories
I was wandering on what exactly the categories for match quality (Poor, Fair, Good, Excellent) are based.
When NIST searches for compounds it gives a percentage of probability to that match for each library used, but it doesn't seem to have a pattern in the Paradise report according to that.
Thank you.
Dear Guest,
The categories for match quality are based on the NISTMS manual, see for instance the NIST17 manual, which under section "Basis for Interpretation of the Library Search Results" - page 41 - writes:
"Each is derived from a modified cosine of the angle between the spectra (normalized dot product). A perfect match results in a value of 999; spectra with no peaks in common result in a value of 0. As a general guide, 900 or greater is an excellent match; 800–900, a good match; 700–800, a fair match. Less than 600 is a very poor match".
The mentioned section describes this in detail and also discusses the Probability value that is associated with each search result.
Note, that since the match factor (and reverse match factor) are by definition between 0 and 1000, one can without loss of generality divide it by 10 and think of it as the probability of a compound matching the library spectra.
Best,
Jesper