I am working on finding the sentiment of some text. Right now I am using a python library called VADER that for each sentence it gives me back the probability that a specific phrase is positive, negative, or neutral. The library itself gives you a sentiment compound but for my application, the default implementation is not working good so I have to develop my personal compound.
My question is there a way that given the following information: length of the sentence, probability of positive, probability of neutral, probability of negative I can calculate a general probability of the sentiment of the phrase? This value later will be standardized between -1 and 1.
For example, the sentence "There are some great sets to await; nevertheless I'm really disappointed about us still not getting a TV broadcast van a post van and a pisten bully" the library gives me these probabilities 'neg': 0.188, 'neu': 0.655, 'pos': 0.157.
My logic would say that the sentence is neutral or slightly negative.
I have tried to use the formula of probabilities of three events occurring together but I am not sure about it.