1. 1. P. Balaji, O. Nagaraju, and D. Haritha, "Levels of sentiment analysis and its challenges: A literature review," 2017 International Conference on Big Data Analytics and Computational Intelligence (ICBDAC), Chirala, 2017, pp. 436-439.
   2. Doaa Mohey El-Din Mohammed Hussein, “A survey on sentiment analysis challenges,” 2016
   3. Chandni, Nav Chandra, Srishti Gupta, Renuka Pahade, "Sentiment Analysis and its challenges," 2015 International Journal of Engineering Research and Technology (IJERT).
   4. Haseena Rahmath P, “Opinion Mining and Sentiment Analysis- Challenges and Applications,” 2014 International Journal of Application or Innovation in Engineering & Management (IJAIEM).
   5. A. M. Abirami and V. Gayathri, "A survey on sentiment analysis methods and approach," 2016 Eighth International Conference on Advanced Computing (ICoAC), Chennai, 2017, pp. 72-76. doi: 10.1109/ICoAC.2017.7951748
   6. Mr. Saifee Vohra, Prof. Jay Teraiya, "Applications and Challenges for Sentiment Analysis: A survey," 2013 International Journal of Engineering Research and Technology (IJERT).
   7. Z. Nanli, Z. Ping, L. Weiguo, and C. Meng, “Sentiment analysis: A literature review,” 2012 International Symposium on Management of Technology (ISMOT), Hangzhou, 2012, pp.572-576.
   8. M. S. Neethu and R. Rajasree, "Sentiment analysis in twitter using machine learning techniques," 2013 Fourth International Conference on Computing, Communications and Networking Technologies (ICCCNT), Tiruchengode, 2013, pp. 1-5.
   9. P. D. Turney, “Thumbs up or thumbs down?: semantic orientation applied to unsupervised classification of reviews,” in Proceedings of the 40th annual meeting on association for computational linguistics, pp. 417–424, Association for Computational Linguistics, 2002.
   10. J. Kamps, M. Marx, R. J. Mokken, and M. De Rijke, “Using wordnet to measure semantic orientations of adjectives,” 2004.
   11. C. Fellbaum, “Wordnet: An electronic lexical database (language, speech, and communication),” 1998.
   12. Bing Liu, "Sentiment Analysis and Opinion Mining," in Sentiment Analysis and Opinion Mining , 1, Morgan & Claypool, 2012, pp.167-
   13. H. P. Patil and M. Atique, "Sentiment Analysis for Social Media: A Survey," 2015 2nd International Conference on Information Science and Security (ICISS), Seoul, 2015, pp. 1-4.