5.4.4 Discussion 5.5 Summar III Influence of Items 6 The Idea of Item Influence in Recommender Systems 6.2 Approaches for Computing Item Infuence 6.2. 1 POPULARItY 622EN 888889 6.2.3 Information Theoretic Measures 6.2.3.1 Entropy 6.2.3.2 ENTROPYO: Entropy Considering Missing values 6.2.3.3 HELF: Harmonic mean of Entropy and Logarithm of Frequency 95 6.2.3.4 IGCN: Information Gain through Clustered Neighbors 6. 3 Empirical Study 6.3.1 Procedure 102 6.3.1.1 Preparing Data 6.3. 1.2 Computing influence measures from data 6.3.1.3 Evaluation 6.3.2 Results 6.4 Discussion 6.5 Summary 113 Iv Online Experiments with Influence 114 7 Learning Preferences of New Users 115 7.1 Introduction 7.2 Offline Experiments 7.2.1 Data 7.2.2 Procedure 2.3 Results 7. 2.4 Discussion 128 7.3 Online Experiments 128 Reproduced with permission of the copyright owner. Further reproduction prohibited without permissionReproduced with permission of the copyright owner. Further reproduction prohibited without permission