What does the E-value indicate when searching a sequence database?

The E-value, or expect value, reflects the number of hits one can expect to see purely by chance when searching a sequence database. A lower E-value indicates that the match is more significant, meaning that it is less likely to have occurred randomly. This metric helps researchers assess the statistical significance of their sequence alignments. For instance, if an E-value is 1, it suggests that, given the size of the database and the characteristics of the search query, one would expect to find one alignment of that quality by random chance. Therefore, the E-value provides valuable insight into the reliability of the alignment results, indicating how much confidence a researcher can have in the hit obtained in relation to their query.