Abstract: The rise in popularity and ubiquity of Twitter has made sentiment analysis of tweets an important and well-covered area of research. However, the 140 character limit imposed on tweets makes it hard to use standard linguistic methods for sentiment classification. On the other hand, what tweets lack in structure they make up with sheer volume and rich metadata. This metadata includes geolocation, temporal and author information. We hypothesize that sentiment is dependent on all these contextual factors. Different locations, times and authors have different emotional valences. In this paper, we explored this hypothesis by utilizing distant supervision to collect millions of labelled tweets from different locations, times and authors. We used this data to analyse the variation of tweet sentiments across different authors, times and locations. Once we explored and understood the relationship between these variables and sentiment, we used a Bayesian approach to combine these variables with more standard linguistic features such as n-grams to create a Twitter sentiment classifier. This combined classifier outperforms the purely linguistic classifier, showing that integrating the rich contextual information available on Twitter into sentiment classification is a promising direction of research.

Introduction: Twitter is a micro-blogging platform and a social network where users can publish and exchange short messages of up to 140 characters long (also known as tweets). Twitter has seen a great rise in popularity in recent years because of its availability and ease-of-use. This rise in popularity and the public nature of Twitter (less than 10% of Twitter accounts are private BIBREF0 ) have made it an important tool for studying the behaviour and attitude of people. One area of research that has attracted great attention in the last few years is that of tweet sentiment classification. Through sentiment classification and analysis, one can get a picture of people's attitudes about particular topics on Twitter. This can be used for measuring people's attitudes towards brands, political candidates, and social issues. There have been several works that do sentiment classification on Twitter using standard sentiment classification techniques, with variations of n-gram and bag of words being the most common. There have been attempts at using more advanced syntactic features as is done in sentiment classification for other domains BIBREF1 , BIBREF2 , however the 140 character limit imposed on tweets makes this hard to do as each article in the Twitter training set consists of sentences of no more than several words, many of them with irregular form BIBREF3 . On the other hand, what tweets lack in structure they make up with sheer volume and rich metadata. This metadata includes geolocation, temporal and author information. We hypothesize that sentiment is dependent on all these contextual factors. Different locations, times and authors have different emotional valences. For instance, people are generally happier on weekends and certain hours of the day, more depressed at the end of summer holidays, and happier in certain states in the United States. Moreover, people have different baseline emotional valences from one another. These claims are supported for example by the annual Gallup poll that ranks states from most happy to least happy BIBREF4 , or the work by Csikszentmihalyi and Hunter BIBREF5 that showed reported happiness varies significantly by day of week and time of day. We believe these factors manifest themselves in sentiments expressed in tweets and that by accounting for these factors, we can improve sentiment classification on Twitter. In this work, we explored this hypothesis by utilizing distant supervision BIBREF6 to collect millions of labelled tweets from different locations (within the USA), times of day, days of the week, months and authors. We used this data to analyse the variation of tweet sentiments across the aforementioned categories. We then used a Bayesian approach to incorporate the relationship between these factors and tweet sentiments into standard n-gram based Twitter sentiment classification. This paper is structured as follows. In the next sections we will review related work on sentiment classification, followed by a detailed explanation of our approach and our data collection, annotation and processing efforts. After that, we describe our baseline n-gram sentiment classifier model, followed by the explanation of how the baseline model is extended to incorporate contextual information. Next, we describe our analysis of the variation of sentiment within each of the contextual categories. We then evaluate our models and finally summarize our findings and contributions and discuss possible paths for future work.

Question: What is the relationship between author and emotional valence?
Answer: Among those who wrote more than 50 tweets, 16% of the authors have average sentiment within [0.95, 1.00], while only 1.5% of the authors have average sentiment within [-1.00, -0.95]