In the pre-processing step, all the English language reviews were converted into lowercase. Special symbols, words with
one character length and other unnecessary characters were eliminated from each review document. In the feature extraction
step, unigram and bi-gram patterns were extracted as sentimental patterns. To reduce the computational complexity,
especially in density estimation, we performed feature selection using the information gain technique [37]. We selected
5000 high score unigrams and bi-grams as final features. Each document was represented by a feature vector. Each entry
of a feature vector contained a feature weight. We used term presence as feature weights since this method has been confirmed
as the most effective feature weighting method in sentiment classification [26,36].