Expect value: Difference between revisions
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The Expect Value (E) is the number of hits that a person would expect by chance when searching a [[Database|database]]. The lower this value is, the higher the Score (S) of the match is. The closer the E-value gets to zero, the better the match is. You can increase or decrease it, depending on how small your sequences are, for example if you are searching smaller sequences, you could increase the E value from 10 to 1000. | The Expect Value (E) is the number of hits that a person would expect by chance when searching a [[Database|database]]. The lower this value is, the higher the [[Score (S) - BLAST|Score (S)]] of the match is. The closer the [[E-value - BLAST|E-value]] gets to zero, the better the match is. You can increase or decrease it, depending on how small your sequences are, for example if you are searching smaller sequences, you could increase the E value from 10 to 1000. | ||
The lower the E-value, or the closer it is to zero, the more "significant" the match is. But another factor that affects the E-value is the length of query. Since shorter ones have a higher chance of occurring in the database, they tend to have a higher E-value <ref>National Library of Medicine, BLAST Frequently Asked Questions [online], available at: http://www.ncbi.nlm.nih.gov/blast/</ref>. | The lower the E-value, or the closer it is to zero, the more "significant" the match is. But another factor that affects the E-value is the length of query. Since shorter ones have a higher chance of occurring in the database, they tend to have a higher E-value <ref>National Library of Medicine, BLAST Frequently Asked Questions [online], available at: http://www.ncbi.nlm.nih.gov/blast/</ref>. | ||
Revision as of 11:47, 19 October 2016
The Expect Value (E) is the number of hits that a person would expect by chance when searching a database. The lower this value is, the higher the Score (S) of the match is. The closer the E-value gets to zero, the better the match is. You can increase or decrease it, depending on how small your sequences are, for example if you are searching smaller sequences, you could increase the E value from 10 to 1000.
The lower the E-value, or the closer it is to zero, the more "significant" the match is. But another factor that affects the E-value is the length of query. Since shorter ones have a higher chance of occurring in the database, they tend to have a higher E-value [1].
References
- ↑ National Library of Medicine, BLAST Frequently Asked Questions [online], available at: http://www.ncbi.nlm.nih.gov/blast/