Evaluation of recommender systems in streaming environments

Evaluation of recommender systems is typically done with finite datasets. This means that conventional evaluation methodologies are only applicable in offline experiments, where data and models are stationary. However, in real world systems, user feedback is continuously generated, at unpredictable rates. Given this setting, one important issue is how to evaluate algorithms in such a streaming data environment. In this paper we propose a prequential evaluation protocol for recommender systems, suitable for streaming data environments, but also applicable in stationary settings. Using this protocol we are able to monitor the evolution of algorithms' accuracy over time. Furthermore, we are able to perform reliable comparative assessments of algorithms by computing significance tests over a sliding window. We argue that besides being suitable for streaming data, prequential evaluation allows the detection of phenomena that would otherwise remain unnoticed in the evaluation of both offline and online recommender systems.Comment: Workshop on 'Recommender Systems Evaluation: Dimensions and Design' (REDD 2014), held in conjunction with RecSys 2014. October 10, 2014, Silicon Valley, United State

How we got Here? A Methodology to Study the Evolution of Economies

This paper proposes a methodology to analyze the evolution of the economic development of countries. Our approach is based upon the definition of temporal trajectories of countries in a common bidimensional space yielded by a High-Order Singular Value Decomposition (HOSVD). These trajectories are defined with respect to a pre-selected set of macroeconomic indicators and are appropriate for comparison purposes. To show the applicability of the proposed methodology we have used data from the World Bank concerning the economic and financial development of EU-27 over a 14-year span, that goes from 1995 to 2008. Based on this data we group the EU-27 state members according to their economic development, which is indicated by the position of their trajectories on the plane. We further perform individual analyses of the trajectories of Luxembourg, Germany and Portugal, aiming to both detect and interpret trends and changes in these economies. The results show that this methodology is of importance for economic studies, since it can help the design, monitoring and evaluation of specific economic policies, as well as provide an overview of the evolution of the studied economic phenomenon.European Union, HOSVD, International Comparisons, Temporal Trajectories

Clinical profile in schizophrenia spectrum : relation with unconjugated bilirubin (UCB) and other psychophysiological features - a longitudinal exploratory study

Objectivo: O nosso objectivo consistiu em avaliar a bilirrubina não conjugada (UCB) como candidato a biomarcador no espectro e na gravidade da esquizofrenia e perturbação esquizoafectiva. Para esse fim preparámos dois estudos: um estudo transversal restrospetivo de cinco anos, e um estudo longitudinal prospectivo com um ano de duração. Métodos: No nosso estudo transversal retrospetivo de 5 anos procurámos correlação entre os níveis médios de UCB, duração média de internamento e o diagnóstico em 255 indivíduos, incluindo 56 controlos saudáveis e 199 doentes (nomeadamente 44 com esquizofrenia, 99 com perturbação esquizoafectiva e 56 com perturbação bipolar). No nosso estudo longitudinal prospetivo 88 doentes psicóticos completaram a primeira avaliação durante internamento psiquiátrico em contexto de episódio psicótico agudo, metade com esquizofrenia, metade com perturbação esquizoafectiva. Nesta fase 44 doentes com perturbação bipolar, foram usados como controlos. Aos doze meses de seguimento completámos o protocolo longitudinal (dados laboratoriais, psicopatológicos e psicossociais) de 60 doentes, metade com esquizofrenia, metade com perturbação esquizoafectiva. Resultados: No nosso estudo transversal retrospetivo de 5 anos encontrámos diferença estatisticamente significativa, após teste de multicomparações de Bonferroni, entre os níveis médios de UCB dos doentes com esquizofrenia (0.41 mg/dL) e os doentes com perturbação esquizoafectiva (0.34 mg/dL) (p<0.03), os doentes com perturbação bipolar (0.28mg/dL) (p<0.001) e também os controlos saudáveis (0.28) (p<0.001). Encontrámos ainda diferença estatisticamente significativa entre os níveis médios de UCB de doentes com perturbação esquizoafectiva (0.34 mg/dL) e perturbação bipolar (0.28 mg/dL) (p<0.04). Relativamente à duração média de internamentos durante o período dos 5 anos, ao diagnóstico e ao nível de UCB, quando aplicámos um modelo de regressão linear ANOVA, com a duração média dos internamentos como variável dependente, encontrámos uma diferença estatisticamente significativa (p<0.001) entre os doentes com esquizofrenia (29 dias) e os doentes com perturbação bipolar (16 dias) mas não com os doentes com perturbação esquizoafectiva. No nosso estudo longitudinal prospetivo de 1 ano, encontrámos, aquando da primeira avaliação durante o episódio psicótico agudo (N=88): uma diferença estatisticamente significativa (ANOVA; p=0.002), confirmada após teste de multicomparações de Bonferroni, entre doentes com esquizofrenia (N=44), quer com os doentes com perturbação esquizoafectiva (N=44) (p=0.05), quer com os controlos com perturbação bipolar (N=44) (p=0.05). Encontrámos também uma correlação positiva (Pearson’s r=0.314) entre os valores médios de UCB e o item d) “disturbing and aggressive behavior” da escala de Personal and Social Performance; e ainda uma correlação positiva (R2=0.223), com significância estatística (p=0.008), entre os níveis médios de UCB e a duração média de internamento psiquiátrico dos doentes com perturbação esquizoafectiva que completaram o protocolo (N=30). Durante a remissão parcial, aquando da segunda avaliação (N=60), encontrámos: uma diferença estatisticamente significativa (ANOVA; p=0.006), confirmada após teste de multicomparações de Bonferroni (p=0.05) entre os doentes com esquizofrenia (N=30) e perturbação esquizoafectiva (N=30); bem como uma correlação negativa (Pearson’s r=−0.399) entre os níveis médios de UCB e o item G7 “psychomotor retardation” da Positive And Negative Syndrome Scale. Ao compararmos a primeira com a segunda avaliação (teste T Student para amostras emparelhadas) encontrámos uma diferença estatisticamente significativa (p=0.034) nos valores médios apenas entre doentes com perturbação esquizoafectiva (N=30). Conclusão: existe um interessante potencial na investigação da UCB como biomarcador das psicoses e respectiva gravidade, quer no espectro da esquizofrenia, quer no da perturbação esquizoafectiva, seja na recaída ou na remissãoObjective: Our objective was to assess unconjugated bilirubin (UCB) as a biomarker candidate for schizophrenia and schizoaffective spectrums disorder and its clinical severity. For that purpose we prepared two different studies: a five year transversal restrospective study, and a one year longitudinal prospective study. Methods: For our five years transversal restrospetive study we searched for an eventual correlation between UCB mean levels, duration of psychiatric admission, and diagnosis in 255 individuals, including 56 healthy controls and 199 acute patients (namely 44 with schizophrenia, 99 with schizoaffective disorder and 56 with bipolar disorder). For our one year longitudinal prospective study 88 psychotic patients completed a first assessment during relapse at ward admission, half with schizophrenia half with schizoaffective disorder. Forty−four acute bipolar patients were used as controls. In a twelve−month follow−up we collected longitudinal protocol (laboratory, psychopathological and psychosocial data) from 60 of those patients, half with schizophrenia half with schizoaffective disorder. Results: In our five year transversal retrospective study we found a statistically significant difference between UCB mean levels of patients with schizophrenia (0.41 mg/dL) versus patients with schizoaffective (0.34 mg/dL) (p<0.03), bipolar disorders (0.28mg/dL) (p<0.001) and healthy controls (0.28)(p<0.001) using Bonferroni multiple comparison test. We also found a statistically significant difference (p<0.04) between UCB mean levels of patients with schizoaffective disorder (0.34 mg/dL) and bipolar disorder (0.28 mg/dL). Regarding average admissions duration for the five−year period, diagnosis and UCB level, when applying a linear regression ANOVA model, with average admissions duration as a dependent variable we found statistically significant difference between schizophrenia (29 days) versus bipolar (16 days) (p<0.001) but not with patients with schizoaffective disorder. In our one year longitudinal prospective study during acute psychotic episode (N=88) we found: a statistically significant difference (ANOVA; p=0.002), confirmed after post−hoc Bonferroni multiple comparisons between between UCB mean levels of schizophrenia (N=44) and both schizoaffective (N=44) (p=0.05) and bipolar controls (N=44) (p=0.05); a positive Pearson’s correlation (r=0.314) between UCB mean levels and Personal and Social Performance item d) “disturbing and aggressive behavior”; and a positive correlation (R2=0.223), with statistically significance (p=0.008), between UCB mean levels and mean length of stay at the psychiatric ward in schizoaffective patients who completed full protocol (N=30). During partial remission (N=60) we found: a statistically ANOVA significant difference (p=0.006), confirmed after post−hoc Bonferroni multiple comparisons between between UCB mean levels of schizophrenia (N=30) and schizoaffective (N=30) (p=0.05); plus a negative Pearson’s correlation (r=−0.399) between UCB mean levels and Positive And Negative Syndrome Scale item G7 “psychomotor retardation”. Comparing first and second assessments, with paired samples T−test, we found a statistically significant difference (p=0.034) in UCB mean levels only among patients with schizoaffective disorder (N=30). Conclusion: there is an interesting potential in the research of UCB as a biological marker for schizophrenia and schizoaffective spectrums disorders, for both relapse and remission episodes of these syndromes

Sudden Trust Collapse in Networked Societies

Trust is a collective, self-fulfilling phenomenon that suggests analogies with phase transitions. We introduce a stylized model for the build-up and collapse of trust in networks, which generically displays a first order transition. The basic assumption of our model is that whereas trust begets trust, panic also begets panic, in the sense that a small decrease in trust may be amplified and ultimately lead to a sudden and catastrophic drop of trust. We show, using both numerical simulations and mean-field analytic arguments, that there are extended regions of the parameter space where two equilibrium states coexist: a well-connected network where confidence is high, and a poorly connected network where confidence is low. In these coexistence regions, spontaneous jumps from the well-connected state to the poorly connected state can occur, corresponding to a sudden collapse of trust that is not caused by any major external catastrophe. In large systems, spontaneous crises are replaced by history dependence: whether the system is found in one state or in the other essentially depends on initial conditions. Finally, we document a new phase, in which agents are connected yet distrustful.Comment: 15 pages, 10 figure

Análise exploratória de hierarquias em base de dados multidimensionais

Cada vez mais, as empresas e organizações utilizam bases de dados multidimensionais e ferramentas OLAP como forma de organizar informação proveniente de sistemas transacionais com o objetivo de aceder e analisar dados com elevada flexibilidade e desempenho. No modelo de dados OLAP, a informação é concetualmente organizada em cubos. Cada dimensão do cubo tem uma hierarquia associada, o que possibilita analisar os dados em diferentes níveis de agregação. Apresenta-se uma metodologia que explora os diferentes níveis de agregação das hierarquias para uma análise exploratória assim como previsões para diferentes horizontes temporais. Esta metodologia mostrou-se muito eficiente, apresentando melhores resultados em comparação com as técnicas usuais de previsão. Os resultados das previsões realizadas são promissores e coerentes com a respetiva análise exploratória.Increasingly, companies and organizations use multidimensional databases and OLAP tools to structure and organize information from transactional systems, with the objective of accessing and analyzing data with high level of flexibility and performance. In the OLAP models, data is conceptually organized into cubes. Each cube’s dimension has an associated hierarchy, which allows for data analysis at different levels of aggregation. A methodology is presented, which explores the different levels of aggregation of the hierarchies for an exploratory analysis as well as the forecasts for different time horizons. This methodology proved to be very efficient, with better results than those obtained from the usual techniques of forecasting. The forecasting results are promising and in line with the respective exploratory analysis

The Application of Hierarchical Clustering Algorithms for Recognition Using Biometrics of the Hand

In data analysis, the hierarchical clustering algorithms are powerful tools allowing to identify natural clusters, often without any priori information of the data structure, and are quite often used because provide a graphical representation of the resulting partitions, a hierarchy or dendrogram, revealing more information than non-hierarchical algorithms that returns a unique partition. Moreover, it is not necessary specify the number of clusters à priori. Cutting the dendrogram in different levels on the hierarchy produces different partitions and also, the use of different clusters aggregation methods for the same data set can produces different hierarchies and hence different partitions. So, several studies have been concerned with validate the resulting partitions comparing them, for instance, by the analysis of cohesion and separation of their clusters. The work presented here focuses on the problem of choosing the best partition in hierarchical clustering. The procedure to search for the best partition is made in the nested set of partitions, defined by the hierarchy. In traditional approaches each partition is defined by horizontal lines cutting the dendrogram at a determined level. In [3] is proposed an improved method, SEP/COP, to obtain the best partition, based on a wide set of partitions. In this paper we discuss these two types of approaches and we do a comparative study using a set of experiments using two-dimensional synthetic data sets and a real-world data set, based on the biometrics of the hands. This database is provided from Bosphorus Hand Database [36], in the context of recognition of the identity of a person by using the features of her hand/biometrics. We conclude that neither of the approaches proved consistently to perform better than the other, but the SEP/COP algorithm showed to be a better partition algorithm in situations like clusters with the approximately the same cardinality and well apart. Also, less depend of the used aggregation criteria and more robust to the presence of noise. Regarding to real data, the results of the experiments demonstrated that SEP/COP hierarchical clustering algorithms approach can contribute to identification systems based on the biometrics of the hands shape