E-value in Blast

pavan · 09-06-2013, 11:35 PM

Hello everybody!!

How blast results very with change in e-value.
If i change e-value from 10 to directly to some value like e10-6(0.000001)

Thanks
Pa1

GenoMax · 09-08-2013, 05:56 AM

I am not sure if there is a question in your post or a statement but if that was a question then refer following:

http://blast.ncbi.nlm.nih.gov/Blast....YPE=FAQ#expect
http://www.ncbi.nlm.nih.gov/BLAST/tu...ltschul-1.html

Melissa · 09-08-2013, 09:59 AM

You are asking how does reducing the E-value change your blast results if I understand correctly. When you change the E-value from 10 to 1E-6, you will remove results which are less significant and thus, you get lower number of results. The smaller the E-value, the more significant is the result. The smallest E-value you can get is 0.0. If two results contain E-value 0.0, I would look at the scores to find the most significant results.

A_Morozov · 09-09-2013, 10:09 PM

Yeah, one more thing to keep in mind. E-value setting does not affect parameters of the alignment, it just makes BLAST display more or less hits.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
BLAST+ creating custom blast database and using blast+ filtering features	deniz	Bioinformatics	3	07-07-2019 09:04 AM
blast against Repbase using Repeatmasker or blast	lran2008	Bioinformatics	1	08-16-2013 07:52 AM
BLAST help	horvathdp	Bioinformatics	1	12-14-2011 08:33 AM
BLAST+ vs BLASTALL (legacy BLAST)	Symphysodon	Bioinformatics	4	10-25-2011 03:52 PM
BLAST database error - when changing to new BLAST+ local program	biobio	Bioinformatics	4	06-15-2011 06:20 AM

09-06-2013, 11:35 PM	#1
pavan Junior Member Location: Bangaluru Join Date: Nov 2012 Posts: 9	E-value in Blast Hello everybody!! How blast results very with change in e-value. If i change e-value from 10 to directly to some value like e10-6(0.000001) Thanks Pa1

09-08-2013, 05:56 AM	#2
GenoMax Senior Member Location: East Coast USA Join Date: Feb 2008 Posts: 7,081	I am not sure if there is a question in your post or a statement but if that was a question then refer following: http://blast.ncbi.nlm.nih.gov/Blast....YPE=FAQ#expect http://www.ncbi.nlm.nih.gov/BLAST/tu...ltschul-1.html

09-08-2013, 09:59 AM	#3
Melissa Senior Member Location: Switzerland Join Date: Aug 2008 Posts: 124	You are asking how does reducing the E-value change your blast results if I understand correctly. When you change the E-value from 10 to 1E-6, you will remove results which are less significant and thus, you get lower number of results. The smaller the E-value, the more significant is the result. The smallest E-value you can get is 0.0. If two results contain E-value 0.0, I would look at the scores to find the most significant results.

09-09-2013, 10:09 PM	#4
A_Morozov Member Location: Russia, Irkutsk Join Date: Feb 2011 Posts: 40	Yeah, one more thing to keep in mind. E-value setting does not affect parameters of the alignment, it just makes BLAST display more or less hits.