Regarding the E value displayed in the BLAST analysis results: How is this value calculated?

Last updated:2017.4.13.

The E value is computed using the following formula, in which l denotes the length of the query string, n denotes the number of strings stored in the database, and S is a score that measures the homology between nucleic acids or between amino acids. Note that k and m are positive constants.

E=k*l*n*exp^(-mS)

If the BLAST output results computed using this formula are displayed in the form 1E-X, this means that the quantity has the value 10-X.

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