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Frontiers of Computer Science

ISSN 2095-2228

ISSN 2095-2236(Online)

CN 10-1014/TP

Postal Subscription Code 80-970

2018 Impact Factor: 1.129

Front. Comput. Sci.    2024, Vol. 18 Issue (5) : 185603    https://doi.org/10.1007/s11704-023-2655-2
RESEARCH ARTICLE
How graph convolutions amplify popularity bias for recommendation?
Jiajia CHEN1, Jiancan WU1, Jiawei CHEN2, Xin XIN3, Yong LI4, Xiangnan HE1()
1. School of Information Science and Technology, University of Science and Technology of China, Hefei 230026, China
2. School of Computer Science and Technology, Zhejiang University, Hangzhou 310058, China
3. School of Computer Science and Technology, Shandong University, Qingdao 250100, China
4. Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
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Abstract

Graph convolutional networks (GCNs) have become prevalent in recommender system (RS) due to their superiority in modeling collaborative patterns. Although improving the overall accuracy, GCNs unfortunately amplify popularity bias — tail items are less likely to be recommended. This effect prevents the GCN-based RS from making precise and fair recommendations, decreasing the effectiveness of recommender systems in the long run.

In this paper, we investigate how graph convolutions amplify the popularity bias in RS. Through theoretical analyses, we identify two fundamental factors: (1) with graph convolution (i.e., neighborhood aggregation), popular items exert larger influence than tail items on neighbor users, making the users move towards popular items in the representation space; (2) after multiple times of graph convolution, popular items would affect more high-order neighbors and become more influential. The two points make popular items get closer to almost users and thus being recommended more frequently. To rectify this, we propose to estimate the amplified effect of popular nodes on each node’s representation, and intervene the effect after each graph convolution. Specifically, we adopt clustering to discover highly-influential nodes and estimate the amplification effect of each node, then remove the effect from the node embeddings at each graph convolution layer. Our method is simple and generic — it can be used in the inference stage to correct existing models rather than training a new model from scratch, and can be applied to various GCN models. We demonstrate our method on two representative GCN backbones LightGCN and UltraGCN, verifying its ability in improving the recommendations of tail items without sacrificing the performance of popular items. Codes are open-sourced

See github.com/MEICRS/DAP website.

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Keywords recommendation      graph convolution networks      popularity bias     
Corresponding Author(s): Xiangnan HE   
Just Accepted Date: 30 May 2023   Issue Date: 31 July 2023
 Cite this article:   
Jiajia CHEN,Jiancan WU,Jiawei CHEN, et al. How graph convolutions amplify popularity bias for recommendation?[J]. Front. Comput. Sci., 2024, 18(5): 185603.
 URL:  
https://academic.hep.com.cn/fcs/EN/10.1007/s11704-023-2655-2
https://academic.hep.com.cn/fcs/EN/Y2024/V18/I5/185603
Fig.1  Performance change of LightGCN with different graph convolution layers on Gowalla. Recall@20 and TR@20 stand for the overall recall score and the ratio of tail items in the top-20 recommendation list, respectively
U, I User set, item set
Nu, Ni The one-order neighbors of user u or item i
du, di The degree of user u or item i
eu(l), ei(l) The embedding of user u or item i at the lth graph convolution layer
Lui The individual loss term of an interaction (u,i)
Cp(l) A set of nodes in the p-th cluster obtained by using Kmeans given the embeddings E(l)
Hv(l) A set of nodes {jCp(l),dj>dv|vCp(l)}
Lv(l) A set of nodes {jCp(l),dj<dv|vCp(l)}
?^Hv(l) The pooling representations after normalization of Hv(l)
?^Lv(l) The pooling representations after normalization of Lv(l)
Tab.1  Main notations used in the paper
Fig.2  Average θ and d32θ in each items group. Items are sorted into groups in ascending order of their degrees. (a) Gowalla; (b) Yelp2018; (c) Amazon-book
Fig.3  The average aggregation weight of one-order neighbor users in each items group. Items are sorted into groups in ascending order of their degrees. (a) Gowalla; (b) Yelp2018; (c) Amazon-book
Dataset #Users #Items #Interactions Density
Gowalla 29,858 40,981 1,027,370 0.00084
Yelp2018 31,668 38,048 1,561,406 0.00130
Amazon-book 52,643 91,599 2,984,108 0.00062
Tab.2  Dataset description
Dataset Gowalla Yelp2018 Amazon-book
Models Overall Tail Overall Tail Overall Tail
Recall NDCG Recall NDCG Recall NDCG Recall NDCG Recall NDCG Recall NDCG
LightGCN 0.1820 0.1546 0.0434 0.0191 0.0627 0.0516 0.0091 0.0046 0.0414 0.0321 0.009 0.0051
BFGCN 0.1083 0.0805 0.0468 0.0245 0.0389 0.0311 0.0124 0.0076 0.0276 0.0211 0.0097 0.0059
LightGCN-IPSCN 0.1325 0.1132 0.0477 0.0213 0.0473 0.0391 0.0136 0.0077 0.0285 0.0221 0.0118 0.0069
LightGCN-CausE 0.1334 0.1137 0.0485 0.0225 0.0492 0.0405 0.0141 0.0085 0.0299 0.0230 0.0127 0.0078
LightGCN-DICE 0.1337 0.1138 0.0493 0.0241 0.0505 0.0409 0.0132 0.0073 0.0348 0.0264 0.0121 0.0074
LightGCN-MACR 0.1188 0.0928 0.0478 0.0219 0.0343 0.027 0.0233 0.0126 0.0269 0.0204 0.0108 0.0065
LightGCN-Tail 0.1647 0.1391 0.0628 0.0319 0.057 0.0466 0.0154 0.0095 0.0369 0.0283 0.0151 0.0094
LightGCN-BxQuAD 0.1378 0.1130 0.0689 0.0360 0.0545 0.0431 0.0209 0.0123 0.0389 0.0304 0.0164 0.0108
LightGCN-DAP-o 0.1834 0.1564 0.0538 0.0245 0.0634 0.0521 0.0137 0.0073 0.0436 0.0339 0.0134 0.0079
LightGCN-DAP-t 0.1672 0.1427 0.0708 0.0354 0.0562 0.0461 0.0218 0.0129 0.0414 0.0328 0.0166 0.0102
Improve/% 0.77 1.16 23.96 28.27 1.12 0.97 50.55 58.70 4.83 5.61 48.89 54.90
Tab.3  Performance comparison between our method DAP and other counterparts on the Overall and Tail test sets. The “improve” is the relative improvement of LightGCN-DAP-o over LightGCN
Dataset Gowalla Yelp2018 Amazon-book
Models Overall Tail Overall Tail Overall Tail
Recall NDCG Recall NDCG Recall NDCG Recall NDCG Recall NDCG Recall NDCG
UltraGCN 0.1862 0.1579 0.0447 0.0213 0.0676 0.0554 0.0127 0.0074 0.0682 0.0556 0.0436 0.0297
UltraGCN-IPSCN 0.1345 0.1123 0.0451 0.0208 0.0401 0.0324 0.0144 0.0087 0.0442 0.0356 0.0458 0.0317
UltraGCN-CausE 0.1408 0.1177 0.0449 0.0209 0.0411 0.0329 0.0151 0.0096 0.0459 0.0369 0.0463 0.0320
UltraGCN-DICE 0.1424 0.1201 0.0512 0.0247 0.0516 0.0417 0.0157 0.0096 0.0545 0.0423 0.0491 0.0343
UltraGCN-MACR 0.1311 0.1078 0.0517 0.0252 0.0387 0.0323 0.0248 0.0141 0.0501 0.0398 0.0488 0.0335
UltraGCN-Tail 0.1788 0.1521 0.0634 0.0321 0.0618 0.0501 0.0167 0.0102 0.0599 0.0499 0.0531 0.0378
UltraGCN-BxQuAD 0.1482 0.1289 0.0694 0.0361 0.0591 0.0482 0.0218 0.0136 0.0623 0.0517 0.0547 0.0386
UltraGCN-DAP-o 0.1868 0.1580 0.0551 0.0271 0.0678 0.0555 0.0135 0.0079 0.0688 0.0562 0.0462 0.0316
UltraGCN-DAP-t 0.1701 0.1483 0.0714 0.0362 0.0607 0.0493 0.0237 0.0135 0.0625 0.0520 0.0543 0.0391
Improve/% 0.32 0.06 5.59 6.57 0.30 0.18 6.30 6.76 0.88 1.07 5.96 6.40
Tab.4  Performance comparison between our method DAP and other counterparts on the Overall and Tail test sets. The “improve” is the relative improvement of UltraGCN-DAP-o over UltraGCN
Fig.4  Performance comparison between LightGCN and LightGCN-DAP with different layers of graph convolution on the Overall test set. (a) Gowalla Recall; (b) Gowalla NDCG; (c) Amazon-book Recall; (d) Amazon-book NDCG
Fig.5  Ablation study of DAP with different hyper-parameters α and β on the Overall test set. (a) Gowalla Recall; (b) Yelp2018 Recall; (c) Amazon-book Recall; (d) Gowalla NDCG; (e) Yelp2018 NDCG; (f) Amazon-book NDCG
Dataset Gowalla Yelp2018 Amazon-book
P Recall NDCG Recall NDCG Recall NDCG
1 0.1819 0.1547 0.0629 0.0517 0.0423 0.0329
5 0.182 0.1548 0.063 0.0518 0.0436 0.0339
10 0.1823 0.1552 0.0633 0.0521 0.0435 0.0339
30 0.1831 0.1563 0.0628 0.0518 0.0435 0.0338
50 0.1834 0.1564 0.0626 0.0517 0.0428 0.0334
70 0.1833 0.1564 0.0623 0.0515 0.0426 0.0331
Tab.5  Effect of P over DAP for the three datasets on the Overall test set
Fig.6  DAP can effectively alleviate the popularity bias. (a) Gowalla; (b) Yelp2018; (c) Amazon-book
  
  
  
  
  
  
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