Using online linear classifiers to filter spam Emails

The performance of two online linear classifiers - the Perceptron and Littlestone’s Winnow – is explored for two anti-spam filtering benchmark corpora - PU1 and Ling-Spam. We study the performance for varying numbers of features, along with three different feature selection methods: Information Gain (IG), Document Frequency (DF) and Odds Ratio. The size of the training set and the number of training iterations are also investigated for both classifiers. The experimental results show that both the Perceptron and Winnow perform much better when using IG or DF than using Odds Ratio. It is further demonstrated that when using IG or DF, the classifiers are insensitive to the number of features and the number of training iterations, and not greatly sensitive to the size of training set. Winnow is shown to slightly outperform the Perceptron. It is also demonstrated that both of these online classifiers perform much better than a standard Naïve Bayes method. The theoretical and implementation computational complexity of these two classifiers are very low, and they are very easily adaptively updated. They outperform most of the published results, while being significantly easier to train and adapt. The analysis and promising experimental results indicate that the Perceptron and Winnow are two very competitive classifiers for anti-spam filtering

Bullying contextualized: how classroom contexts Influence bullying and Its consequences

Bullying refers to aggressive goal-directed behavior that harms another individual within the context of a power imbalance. Bullying has been viewed as a group process. One of main motivation of bullying is to gain social dominance in the peer group. Moreover, the features of classroom environment could shape the emergence and maintenance of bullying and victimization, as well as their consequences. Using data from 3H project, Study Ⅰ examined whether classroom status hierarchy moderated the longitudinal association between social dominance goals and bullying behavior. I found children who oriented to social dominance goals are more likely to engage in bullying when power is less equally distributed in the classroom, controlling for gender, grade, classroom size, and classroom gender distribution. With three-year longitudinal design, Study Ⅱ tested the effects of time-varying and time-invariant components of social dominance goal on bullying and the moderating roles of classroom bystanders’ behavior. The results revealed that both persistent and temporary social dominance goals might motivate children to exhibit bullying behavior, but peers’ defending behaviors mitigate these associations. Finally, Study Ⅲ paid attention on how classroom features influence on the consequences of victimization. The finding from Study Ⅲ provide support for the hypothesis of “healthy context paradox” — peer victimization was more strongly associated with increasing depressive symptoms in classrooms with lower classroom-level victimization. Moreover, two mechanisms of this phenomenon were identified. First, low classroom-level victimization reduced victimized children’s received friendship nominations from peers, thereby leading to increases in depressive affect. Second, low classroom-level victimization affected victimized children’s depressive symptoms through damage to their social self-concept. Taken together, these findings provide evidence regarding the group nature of bullying and highlight contextual factors which contribute to bullying dynamics