Enter the length of the query sequence, the total number of lengths of all template sequences, and the bit score into the calculator to determine the E Value.

E value Formula

The following formula is used to calculate an E-value in BLAST.

E = m*n*2^{-S}
  • Where E is the e-value
  • m is the length of the query sequence
  • n is the total number of lengths of all template sequences in file
  • S is the bit score

What is an E-Value (computer science)?

E-Value in computer science is a numerical representation of the expected utility or benefit of a specific action or decision within a given system or algorithm.

This value is calculated using various algorithms, statistical models, or machine learning techniques, depending on the context. It serves as a measure of the potential outcome or value that can be derived from a particular choice.

E-Value is crucial in computer science as it enables efficient decision-making and optimization across various applications.

By quantifying the potential benefits of different options, it helps algorithms prioritize actions likely to yield the best results, leading to improved performance and resource allocation.

In fields like artificial intelligence, E-Value plays a vital role in reinforcement learning algorithms. These algorithms aim to maximize a cumulative reward by learning from interactions with an environment.

E-Value guides the decision-making process by evaluating the expected rewards associated with different actions, allowing the algorithm to select the most promising ones.

This is particularly valuable in scenarios where exploration and exploitation must be balanced to achieve optimal outcomes.

Example Problem

How to calculate E-Value?

First, determine the length of the query sequence. For this example, the sequence length is found to be 10.

Next, determine the total number of lengths in all of the template sequences in the file. For this problem, this value is 50.

Next, determine the bit score. We will use 3.

Finally, calculate the e-value using the formula:


= 10 *50*2^-3

= 62.5.


What is the significance of the bit score in calculating the E-Value?
The bit score represents the raw alignment score between sequences, adjusted for the database size and the scoring system used. It is crucial in calculating the E-Value as it directly influences the expected number of chance matches in a database search, helping to assess the significance of the match.

How does the length of the query sequence affect the E-Value?
The length of the query sequence (m) is directly proportional to the E-Value. The longer the query sequence, the higher the probability of finding matches by chance, which increases the E-Value. This makes it an essential factor in evaluating the statistical significance of the match.

Can the E-Value be used to compare the significance of different matches?
Yes, the E-Value is a key metric for comparing the significance of different matches in bioinformatics searches. Lower E-Values indicate a higher significance of the match, implying that the observed alignment is less likely to have occurred by chance.

Why is the total number of lengths of all template sequences important in the E-Value calculation?
The total number of lengths of all template sequences (n) represents the size of the search space or database. It is important in the E-Value calculation because a larger search space increases the chance of finding matches by chance, thereby affecting the E-Value. This parameter helps in normalizing the E-Value across searches of different database sizes.

e value calculator