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About Semantria's Sentiment Analysis

Last Updated: May 16, 2013 01:55PM EDT
What is sentiment polarity and sentiment score?
The sentiment polarity is a verbal representation of the sentiment. It can be "negative", "neutral", or "positive".

The sentiment score is a more precise numerical representation of the sentiment polarity. To understand how it is calculated, see below.

Sentiment polarity and scores are available for documents, named entities, themes, and queries.

How is sentiment score calculated? 
Semantria uses a logarithmic scale for sentiment. In contrast to a linear scale that has values with the linear step, where the next value will always be higher than the previous one on the same constant value, let’s say 1, 2, 3, etc.

A logarithmic scale has a completely different spread where each next value has an exponential increase. For a decimal logarithm multiplier of 10, the scale would be 1, 10, 100, 1000, etc. 

So if we know that -10 is the most negative and 10 is the most positive we can calculate logarithmic scale of sentiment score modulo which is spread between -1 and 1.

Let’s say on negative scale very bad is 5, and a nightmare is 10, this would give you log(5)*-1 = 0.69 * -1 = -0.69. -1 is the mandatory multiplier for the negative scale.

How to determine whether Sentiment is negative or not?
Lexalytics Salience core determines two different sentiment scores that depend on the target object. There are document and component sentiment scores.

Components are themes, topics, and entities - their sentiment is spread over the range of -10 to 10.

The document sentiment has a range spread from -2 to 2, where -2 is really negative, -1 is negative, 1 is positive, and 2 is really positive.

Component sentiment: Negative < -0.45, Positive > 0.5
Document sentiment: Negative < -0.05, Positive > 0.22

Are there any best practices around confidence and evidence scores?
This is all done automatically. The confidence is an indicator that specifies whether or not the confidence queries matched for a given entity. Evidence scores range from 1 to 7 and give an indication of the amount of content that contributed to the sentiment score. Empirically, the sentiment score is valid if evidence score is equal to or greater than 4.

Can customers modify sentiment bearing phrase dictionaries or is there one dictionary for all users and if modified it affects them all?
It is possible to modify sentiment bearing phrases. Instructions on how to do so can be found in our Sentiment Bearing Phrases article.

Where can I find the sentiment and what is the score value?
Please visit our developer's portal for more information
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