We define the Effective Word Score of score x as

EFWS(x) = N(+x) - N(-x),

where N(x) is the number of words in the tweet with polarity score x. 
 Question: How is effective word score calculated?
We define the Effective Word Score of score x as

EFWS(x) = N(+x) - N(-x),

where N(x) is the number of words in the tweet with polarity score x.