REVIEW 3 major objections 5 minor 43 references
Far From Sight, Far From Mind: Inverse Distance Weighting for Graph Federated Recommendation
T0 review · 3 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read A distance-based aggregation rule for user embeddings improves federated graph recommendation accuracy without significant privacy or speed cost.
desk verdict Readable, but the method never aggregates the same user's embeddings across clients; the headline claim is unsupported. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The carrying mechanism is inverse-distance weighting with anchor interpolation. Distances between user embeddings are computed with Minkowski distance (Eq. 3), a tunable-$p$ generalization of Euclidean and Manhattan distance; weights are the inverse of those distances for users inside the same expanded client graph (Eq. 4); and a row-normalization step converts them into an averaging scheme (Eqs. 5-6). The anchor-user contribution is then blended back in by linear interpolation (Eq. 7), and the interpolation parameter $\alpha$ can be held fixed or decayed so that early, still-random embeddings do not drive the aggregation. The mechanism's job is to make the global user embedding a similarity-weighted summary of local updates rather than a uniform average.
What would settle it
Run the same federated graph recommender used in the experiments on the same five datasets with the weighting rule inverted, giving more weight to users whose embeddings are farther apart, and also with random weights drawn from the same distribution; if Dist-FedAvg fails to beat both, the reported gains are not due to user-similarity weighting.
Extended reading notes
Core claim
At the end of each federated round, the server receives updated user embeddings from selected clients. Dist-FedAvg computes a Minkowski distance matrix $D_{ij}$ between the previous round's global user embeddings, converts distances into averaging weights $W_{ij}=1/D_{ij}$ for users in the same expanded local graph (excluding self), normalizes by row sums, and forms a weighted embedding $e'_{u_i}$. It then interpolates $e'_{u_i}$ with the anchor user's own updated embedding through $e^{(r)}_{u_i}=\alpha e_{u_i,i}+(1-\alpha)e'_{u_i}$, with $\alpha$ fixed, decayed arithmetically, or decayed geometrically. The paper reports higher HR@10 than FedAvg, SimpleAvg, FedMedian, and FedAtt on all five datasets, and higher NDCG@10 on four of the five, while keeping training speed and privacy properties intact.
Load-bearing premise
The load-bearing premise is that the distance between two user embeddings at aggregation time tracks how similar those users really are; if embeddings do not place similar users close together, inverse-distance weighting injects noise rather than signal.
Editorial extensions
If this is right
- Dist-FedAvg can replace the user-embedding aggregation step in existing graph federated recommendation pipelines, leaving local training and item aggregation untouched.
- It reports higher HR@10 than FedAvg, SimpleAvg, FedMedian, and FedAtt on all five datasets, and higher NDCG@10 on four of the five.
- The anchor interpolation keeps the central user's locally learned embedding influential, so the aggregation adapts to evolving user interactions without forgetting the primary user.
- Distances can be computed on-device and only weights transmitted, so the scheme can be adapted to a gradient-based privacy-preserving variant.
Reading between the lines
- Because the scheme only needs user embeddings and pairwise distances, the same weighted-averaging idea could be applied to non-graph federated recommenders such as matrix-factorization or neural collaborative filtering, which the paper notes but does not test.
- A direct next experiment would pair Dist-FedAvg with clustering or random sampling of the distance matrix to cut the $O(n^2)$ pairwise cost of the weighting step at scale.
- Applying the same user-derived weights to item-embedding aggregation is an untested consequence of the method's logic; the paper identifies it as future work.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes Dist-FedAvg, a distance-based aggregation rule for user embeddings in a FedPerGNN-style graph federated recommendation framework. The rule assigns inverse-Minkowski-distance weights to users in a client's expanded subgraph, computes a normalized weighted average, and linearly interpolates the result with the anchor user's own updated embedding using a decaying alpha. The authors compare Dist-FedAvg against FedAvg, SimpleAvg, FedMedian, and FedAtt on five datasets, report NDCG@10 and HR@10 with 95% confidence intervals, and include ablations on client count, alpha decay, and item-aggregation pairing. They claim consistent outperformance and seamless plug-in compatibility.
Significance. If the method as described actually performed cross-client aggregation and consistently improved NDCG@10 and HR@10, it would be a useful, low-overhead contribution: the code is released, the protocol is simple, and the evaluation covers multiple datasets with confidence intervals. However, two load-bearing problems prevent this assessment. First, Equations (4)-(7) define an intra-client averaging operation that does not combine a user's embeddings across selected clients, so the headline claim that the method combines local updates from different clients is not supported by the algorithm. Second, the paper's own tables contradict the claim of consistent outperformance: on ML-1m and LastFM-2k, Dist-FedAvg is worse than a baseline on one of the two metrics. The ablations and CI reporting are good practice, but they do not repair the mismatch between the claimed federated aggregation and the specified equations.
major comments (3)
- [Section 4, Eqs. (4)-(7) and Algorithm 2] As written, Dist-FedAvg never performs cross-client aggregation for a given user. In Eq. (6), e'_{u_i} is a weighted sum over e_{u_j,i}, the embeddings of users in client c_i's expanded subgraph, with W_{ij} nonzero only when u_j is in U_i; Eq. (7) then blends this with the anchor copy e_{u_i,i}. The copies e_{u_i,j} that Algorithm 1 collects from other selected clients j are never accessed in the aggregation step. Consequently, the output embedding of user u_i in round r is determined exclusively by client c_i's local updates, and information from other clients' current-round updates enters only indirectly through the previous global model E(r-1)_u. This makes Dist-FedAvg an intra-client neighborhood smoother rather than a federated aggregation rule, so the Section 1 claim that it combines local updates from different clients, and the comparison with FedAvg/FedMedian/FedAtt, are not supported by the specified algorithm.
- [Section 5.2, Tables 3 and 4] The abstract and Section 6 state that Dist-FedAvg consistently outperforms all baselines, but the reported numbers do not support this claim. On ML-1m, Dist-FedAvg NDCG@10 = 0.1672 ± 0.0047 is below FedAvg's 0.1678 ± 0.0047; on LastFM-2k, Dist-FedAvg HR@10 = 0.461 ± 0.0225 is below FedMedian's 0.4804 ± 0.0228. Several other comparisons are within overlapping confidence intervals, so even the favorable means should be reported as mixed results or ties, not as consistent wins.
- [Section 4, Algorithm 2 lines 9-13] For users u_i not in C(r), the algorithm sets e(r)_{u_i} = e'_{u_i}. However, e'_{u_i} is defined by Eq. (6) in terms of e_{u_j,i}, the updated embeddings of client c_i's expanded users, and client c_i was not selected in round r, so no current-round embeddings from c_i exist in E(r)_u. The algorithm therefore does not specify what data is used to compute e'_{u_i} for unselected users; it needs an explicit fallback, such as the previous global embedding, to be executable under partial client participation.
minor comments (5)
- [Table 1 and Algorithm 1] The notation E(r)_u is overloaded: it is used both for the set of updated embeddings collected from selected clients and for the global aggregated embedding matrix. Please disambiguate these two objects, for example with E_tilde(r)_u for the collected per-client updates.
- [Figures 2, 3, 4, 5] Figures 2 through 5 contain corrupted or unreadable text in the submitted version (for example, axis labels rendered as sequences such as 'uni0000002f'); these figures need to be regenerated with proper font rendering before the paper can be evaluated on the ablation results.
- [Section 3.3, footnote 3] The footnote acknowledges that incorporating privacy-preserving components such as pseudo-item sampling and differential privacy may introduce noise; the main experiments are conducted in the simplified framework without those components, so the reported gains should be described as gains in that simplified setting rather than as guarantees for a fully privacy-preserving deployment.
- [Section 4, Eq. (7) and Section 5.3] The text says alpha 'starts at 1' during decay, but Eq. (8) uses a tunable alpha_0 and the ablation in Figure 3 includes a 'No Decay' condition; please clarify which alpha schedule and hyperparameter values were used to produce the main results in Tables 3 and 4.
- [Section 4, Eq. (5)] If a client's expanded subgraph contains no users other than the anchor, the normalization factor d_i in Eq. (5) is zero and Eq. (6) is undefined; the authors should specify how this degenerate case is handled.
Circularity Check
No significant circularity: Dist-FedAvg is a heuristic aggregation rule whose empirical claims are benchmarked against external baselines and not derived from its own construction.
full rationale
Dist-FedAvg is presented as a heuristic aggregation rule, not as a derivation of a prediction from first principles. The weighting scheme (Eqs. 3-7) is defined directly as inverse-distance weighting of user embeddings, so the statement that the method assigns higher aggregation weights to users with similar embeddings restates the construction rather than deriving an independent result; this is a design choice, not circularity. The empirical comparison against FedAvg, SimpleAvg, FedMedian, and FedAtt is an external benchmark against standard methods and is not used to define the method. Hyperparameters such as the Minkowski exponent p, the decay parameters, and alpha are tuned per dataset with Bayesian optimization, but the reported gains are on held-out test splits and are not fitted quantities renamed as predictions. The paper contains no load-bearing self-citations: references to FedPerGNN, LightGCN, and aggregation surveys are independent prior work. A separate specification concern exists: Eq. 6 sums only over u_j in U_i, the users in the anchor client's expanded local subgraph, so the implementation as written may not actually combine the same user's embeddings across clients; however, that is a correctness or scope issue rather than a circular reduction of the kind considered here. Consequently, no circular step is exhibited.
Assumptions & free parameters
free parameters (7)
- p =
tuned via Bayesian optimization; fixed value not reported
- alpha_0 =
not reported
- alpha_T =
not reported
- gamma =
not reported
- z =
not reported
- decay_type =
selected per dataset
- warmup_rounds =
not reported
assumptions (4)
- domain assumption Minkowski distance between user embeddings is a meaningful measure of user similarity for aggregation
- ad hoc to paper The anchor user's embedding should retain a tunable share of the aggregated result
- domain assumption Removing privacy mechanisms (pseudo-item sampling, differential privacy) does not change the relative ranking of aggregation methods
- standard math LightGCN with BPR loss is an adequate local recommender for evaluating aggregation rules
Cite this review
Pith. "Pith review of Far From Sight, Far From Mind: Inverse Distance Weighting for Graph Federated Recommendation." pith.science (2026). https://pith.science/paper/XXTOSGME
@misc{pith2026250701285,
author = {Pith},
title = {Pith review of: Far From Sight, Far From Mind: Inverse Distance Weighting for Graph Federated Recommendation},
year = {2026},
howpublished = {\url{https://pith.science/paper/XXTOSGME}},
note = {Machine review of arXiv:2507.01285}
}
read the original abstract
Graph federated recommendation systems offer a privacy-preserving alternative to traditional centralized recommendation architectures, which often raise concerns about data security. While federated learning enables personalized recommendations without exposing raw user data, existing aggregation methods overlook the unique properties of user embeddings in this setting. Indeed, traditional aggregation methods fail to account for their complexity and the critical role of user similarity in recommendation effectiveness. Moreover, evolving user interactions require adaptive aggregation while preserving the influence of high-relevance anchor users (the primary users before expansion in graph-based frameworks). To address these limitations, we introduce Dist-FedAvg, a novel distance-based aggregation method designed to enhance personalization and aggregation efficiency in graph federated learning. Our method assigns higher aggregation weights to users with similar embeddings, while ensuring that anchor users retain significant influence in local updates. Empirical evaluations on multiple datasets demonstrate that Dist-FedAvg consistently outperforms baseline aggregation techniques, improving recommendation accuracy while maintaining seamless integration into existing federated learning frameworks.
Figures
Figures from the paper (1 more)
Reference graph
Works this paper leans on
-
[1]
ACM Transactions on Recommender Systems (Jun 2023).https: //doi.org/10.1145/3651168
AliWaqar, Ammad-ud-dinMuhammad, ZhouXiangmin, ZhangYan, ShaoJie: Communication-Efficient Federated Neural Collaborative Filtering with Multi- Armed Bandits. ACM Transactions on Recommender Systems (Jun 2023).https: //doi.org/10.1145/3651168
-
[2]
Ammad-ud-din, M., Ivannikova, E., Khan, S.A., Oyomno, W., Fu, Q., Tan, K.E., Flanagan, A.: Federated Collaborative Filtering for Privacy-Preserving Person- alized Recommendation System (Jan 2019).https://doi.org/10.48550/arXiv. 1901.09888
-
[3]
IEEE Intelligent Systems 36(5), 11–20 (Sep 2021)
Chai, D., Wang, L., Chen, K., Yang, Q.: Secure Federated Matrix Factorization. IEEE Intelligent Systems 36(5), 11–20 (Sep 2021). https://doi.org/10.1109/ MIS.2020.3014880
-
[4]
Applied Soft Computing 111, 107700 (Nov 2021)
Du, Y., Zhou, D., Xie, Y., Shi, J., Gong, M.: Federated matrix factorization for privacy-preserving recommender systems. Applied Soft Computing 111, 107700 (Nov 2021). https://doi.org/10.1016/j.asoc.2021.107700
arXiv 2021
-
[5]
In: Machine Learning and Knowledge Discovery in Databases
Flanagan, A., Oyomno, W., Grigorievskiy, A., Tan, K.E., Khan, S.A., Ammad- Ud-Din, M.: Federated Multi-view Matrix Factorization for Personalized Recom- mendations. In: Machine Learning and Knowledge Discovery in Databases. pp. 324–347. Springer International Publishing, Cham (2021).https://doi.org/10. 1007/978-3-030-67661-2_20
work page 2021
-
[6]
Guo, G., Zhang, J., Yorke-Smith, N.: A Novel Evidence-Based Bayesian Similarity Measure for Recommender Systems. ACM Trans. Web10(2), 8:1–8:30 (May 2016). https://doi.org/10.1145/2856037
- [7]
- [8]
Show all 43 references
-
[9]
He, X., Liao, L., Zhang, H., Nie, L., Hu, X., Chua, T.S.: Neural Collaborative Filtering. In: WWW. pp. 173–182. WWW ’17, Republic and Canton of Geneva, CHE (Apr 2017).https://doi.org/10.1145/3038912.3052569
2017
- [10]
-
[11]
In: CIKM
Huang, P.S., He, X., Gao, J., Deng, L., Acero, A., Heck, L.: Learning deep struc- tured semantic models for web search using clickthrough data. In: CIKM. pp. 2333–
-
[12]
Egyptian Informatics Journal16(3), 261–273 (Nov 2015)
Isinkaye, F.O., Folajimi, Y.O., Ojokoh, B.A.: Recommendation systems: Principles, methods and evaluation. Egyptian Informatics Journal16(3), 261–273 (Nov 2015). https://doi.org/10.1016/j.eij.2015.06.005
2015 doi
-
[13]
In: IJCNN
Ji, S., Pan, S., Long, G., Li, X., Jiang, J., Huang, Z.: Learning Private Neural Language Modeling with Attentive Aggregation. In: IJCNN. pp. 1–8 (Jul 2019). https://doi.org/10.1109/IJCNN.2019.8852464
2019
-
[14]
Computer42(8), 30–37 (Aug 2009).https://doi.org/10.1109/ MC.2009.263
Koren, Y., Bell, R., Volinsky, C.: Matrix Factorization Techniques for Recom- mender Systems. Computer42(8), 30–37 (Aug 2009).https://doi.org/10.1109/ MC.2009.263
2009
-
[15]
Liang, D., Krishnan, R.G., Hoffman, M.D., Jebara, T.: Variational Autoencoders for Collaborative Filtering. In: WWW. pp. 689–698. WWW ’18, International World Wide Web Conferences Steering Committee, Republic and Canton of Geneva, CHE (Apr 2018).https://doi.org/10.1145/3178876.3186150
2018
-
[16]
IEEE Internet Computing 28(3), 17–24 (May 2024)
Liu, Q., Yang, L., Liu, Y., Deng, J., Wu, G.: Privacy-Preserving Recommendation Based on a Shuffled Federated Graph Neural Network. IEEE Internet Computing 28(3), 17–24 (May 2024)
2024
-
[17]
ACM Transactions on Intelligent Systems and Technology 13(4) (2022)
Liu, Z., Yang, L., Fan, Z., Peng, H., Yu, P.: Federated Social Recommendation with Graph Neural Network. ACM Transactions on Intelligent Systems and Technology 13(4) (2022). https://doi.org/10.1145/3501815
2022 doi
-
[18]
Decision Support Systems74, 12–32 (Jun 2015).https: //doi.org/10.1016/j.dss.2015.03.008
Lu, J., Wu, D., Mao, M., Wang, W., Zhang, G.: Recommender system application developments: A survey. Decision Support Systems74, 12–32 (Jun 2015).https: //doi.org/10.1016/j.dss.2015.03.008
2015 doi
-
[19]
In: AISTATS
McMahan, B., Moore, E., Ramage, D., Hampson, S., y Arcas, B.A.: Communication-Efficient Learning of Deep Networks from Decentralized Data. In: AISTATS. pp. 1273–1282. PMLR (Apr 2017)
2017
-
[20]
In: Proceedings of the 14th ACM Conference on Recommender Systems
Meng, Z., McCreadie, R., Macdonald, C., Ounis, I.: Exploring Data Splitting Strategies for the Evaluation of Recommendation Models. In: Proceedings of the 14th ACM Conference on Recommender Systems. pp. 681–686. RecSys ’20, Asso- ciation for Computing Machinery, New York, NY, ...
2020
-
[21]
In: SIGKDD
Muhammad, K., Wang, Q., O’Reilly-Morgan, D., Tragos, E., Smyth, B., Hurley, N., Geraci, J., Lawlor, A.: FedFast: Going Beyond Average for Faster Training of Federated Recommender Systems. In: SIGKDD. pp. 1234–1242. KDD ’20, Associ- ation for Computing Machinery, New York, NY, ...
2020
-
[22]
Khouas et al
Ni, J., Li, J., McAuley, J.: Justifying Recommendations using Distantly-Labeled ReviewsandFine-GrainedAspects.In:EMNLP-IJCNLP.pp.188–197.Association for Computational Linguistics„ Hong Kong, China (Nov 2019) 16 A.R. Khouas et al
2019
-
[23]
Knowledge-Based Systems 242, 108441 (Apr 2022)
Perifanis, V., Efraimidis, P.S.: Federated Neural Collaborative Filtering. Knowledge-Based Systems 242, 108441 (Apr 2022). https://doi.org/10.1016/ j.knosys.2022.108441
2022
-
[24]
Future Generation Computer Systems 150, 272–293 (Jan 2024)
Qi, P., Chiaro, D., Guzzo, A., Ianni, M., Fortino, G., Piccialli, F.: Model aggrega- tion techniques in federated learning: A comprehensive survey. Future Generation Computer Systems 150, 272–293 (Jan 2024)
2024
-
[25]
In: The Web Conference
Qu, L., Tang, N., Zheng, R., Nguyen, Q.V.H., Huang, Z., Shi, Y., Yin, H.: Semi- decentralized Federated Ego Graph Learning for Recommendation. In: The Web Conference. pp. 339–348. WWW ’23, ACM, New York, NY, USA (Apr 2023)
2023
-
[26]
In: The Web Conference
Qu, L., Yuan, W., Zheng, R., Cui, L., Shi, Y., Yin, H.: Towards Personalized Privacy: User-Governed Data Contribution for Federated Recommendation. In: The Web Conference. pp. 3910–3918. WWW ’24, ACM, New York, NY, USA (May 2024)
2024
-
[27]
Rendle, S., Freudenthaler, C., Gantner, Z., Schmidt-Thieme, L.: BPR: Bayesian personalized ranking from implicit feedback. In: UAI. pp. 452–461. AUAI Press, Arlington, Virginia, USA (Jun 2009)
2009
-
[28]
Sedhain, S., Menon, A.K., Sanner, S., Xie, L.: AutoRec: Autoencoders Meet Col- laborative Filtering. In: WWW. pp. 111–112. WWW ’15 Companion, Association for Computing Machinery, New York, NY, USA (May 2015)
2015
-
[29]
In: RecSys
Shi, Y., Larson, M., Hanjalic, A.: Exploiting user similarity based on rated-item pools for improved user-based collaborative filtering. In: RecSys. pp. 125–132. RecSys ’09, ACM, New York, NY, USA (Oct 2009).https://doi.org/10.1145/ 1639714.1639736
2009
-
[30]
IEEE Transactions on Neural Networks and Learning Systems pp
Sun, Z., Xu, Y., Liu, Y., He, W., Kong, L., Wu, F., Jiang, Y., Cui, L.: A Survey on Federated Recommendation Systems. IEEE Transactions on Neural Networks and Learning Systems pp. 1–15 (2024).https://doi.org/10.1109/TNNLS.2024. 3354924
2024 doi
-
[31]
Wang, X., He, X., Wang, M., Feng, F., Chua, T.S.: Neural Graph Collaborative Filtering.In:SIGIR.pp.165–174.SIGIR’19,AssociationforComputingMachinery, New York, NY, USA (Jul 2019)
2019
-
[32]
In: SIGIR
Wei, Y., Liu, W., Liu, F., Wang, X., Nie, L., Chua, T.S.: LightGT: A Light Graph Transformer for Multimedia Recommendation. In: SIGIR. pp. 1508–1517. SIGIR ’23, Association for Computing Machinery, New York, NY, USA (Jul 2023)
2023
-
[33]
Nature Communications 13(1), 3091 (Jun 2022)
Wu, C., Wu, F., Lyu, L., Qi, T., Huang, Y., Xie, X.: A federated graph neural net- work framework for privacy-preserving personalization. Nature Communications 13(1), 3091 (Jun 2022)
2022
-
[34]
ACM Comput
Wu, S., Sun, F., Zhang, W., Xie, X., Cui, B.: Graph Neural Networks in Recom- mender Systems: A Survey. ACM Comput. Surv.55(5), 97:1–97:37 (Dec 2022)
2022
-
[35]
In: The Web Con- ference
Yan, B., Cao, Y., Wang, H., Yang, W., Du, J., Shi, C.: Federated Heterogeneous Graph Neural Network for Privacy-preserving Recommendation. In: The Web Con- ference. pp. 3919–3929. WWW ’24, ACM, New York, NY, USA (May 2024)
2024
-
[36]
In: Trustworthy Federated Learning
Yang, L., Zhang, J., Chai, D., Wang, L., Guo, K., Chen, K., Yang, Q.: Practical and Secure Federated Recommendation with Personalized Masks. In: Trustworthy Federated Learning. Springer International Publishing (Jun 2022).https://doi. org/10.1007/978-3-031-28996-5_3
2022 doi
-
[37]
In: ICML
Yin, D., Chen, Y., Kannan, R., Bartlett, P.: Byzantine-Robust Distributed Learn- ing: Towards Optimal Statistical Rates. In: ICML. pp. 5650–5659. PMLR (Jul 2018)
2018
-
[38]
Yin, H., Qu, L., Chen, T., Yuan, W., Zheng, R., Long, J., Xia, X., Shi, Y., Zhang, C.: On-Device Recommender Systems: A Comprehensive Survey (Jan 2024) Inverse Distance Weighting for Graph Federated Recommendation 17
2024
- [39]
-
[40]
In: SIGKDD
Zhang, C., Long, G., Zhou, T., Zhang, Z., Yan, P., Yang, B.: GPFedRec: Graph- Guided Personalization for Federated Recommendation. In: SIGKDD. pp. 4131–
-
[41]
In: ICME
Zhang, R., Chen, Y., Wu, C., Wang, F.: Cluster-driven GNN-based Federated Recommendation with Biased Message Dropout. In: ICME. pp. 594–599 (Jul 2023)
2023
-
[2338]
https://doi.org/10.1145/2505515.2505665
CIKM ’13, Association for Computing Machinery, New York, NY, USA (Oct 2013). https://doi.org/10.1145/2505515.2505665
2013
-
[4142]
KDD ’24, ACM, New York, NY, USA (Aug 2024)
2024
Reviewed August 6, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.