REVIEW 4 major objections 6 minor 24 references
LDACP: Long-Delayed Ad Conversions Prediction Model for Bidding Strategy
T0 review · 4 major / 6 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read For long-delayed ad conversions, the paper proposes LDACP, a two-module model that predicts campaign-level conversion counts so automated bidding can use the true expected CPA instead of the stale real-time count.
desk verdict The paper's offline metrics break for the zero-conversion campaigns it is meant to fix; fix that and the industrial story holds. 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
Two sub-modules carried by two distributional observations. BCMS (Bucket Classification Module with label Smoothing) builds on a tree-based bucket classifier but assigns each edge a soft target that varies continuously with distance to the bucket boundary, trained by cross-entropy for hard labels and MSE for soft labels. VRMP (Value Regression Module with Proxy labels) learns $\mathrm{PCOC}=z/y$, the ratio of aggregated pCTCVR to actual conversions, then recovers the predicted count as $\hat{y}_g = z/\hat{\mathrm{PCOC}}$. The MoE gate $\lambda$ is trained with a MAPE loss and shifts weight from the bucket module to the proxy-regression module as the label grows.
What would settle it
Compute the PCOC distribution on a different advertising platform or a different time window from the one used here. If many campaigns show PCOC values far from 1 or a heavy right tail, then VRMP's proxy-label regression loses its advantage; an offline comparison where LDACP fails to beat CREAD-P or TPM-N on such data would falsify the general claim.
Extended reading notes
Core claim
The paper's central claim is that campaign-level conversion counting for long-delayed ads is best done by splitting the task: a bucket classifier whose one-hot labels near bucket boundaries are replaced by smoothly varying soft labels, and a regression head that predicts the ranking model's bias (aggregated predicted conversion rate divided by actual conversions) rather than the raw long-tailed count. Because that bias ratio concentrates in a narrow range with no long tail on the authors' data, ordinary regression works for it, and converting back with the aggregated pCTCVR yields a tail-accurate count. A mixture-of-experts gate then blends the two predictions, weighting the bucket output for small counts and the proxy-regression output for large counts. The result is a single predicted conversion number that the automated bidding system can use in place of the incomplete real-time count.
Load-bearing premise
The whole proxy-regression side rests on an empirical claim: the ranking model's bias ratio PCOC stays in a narrow range with no long tail (Figure 2b on the offline dataset). If that ratio is heavy-tailed or has large outliers on another platform or period, converting back through it will be unstable and the long-tail problem returns.
Editorial extensions
If this is right
- Bidding strategies can react to predicted final conversion counts rather than the small real-time count, avoiding the conservative bids that starve young campaigns of traffic.
- Campaigns with conversion delays of hours to days (e.g., app installs, live-stream actions) get closer to their target CPA, raising the platform's compliance rate.
- The platform's revenue and total conversions rise when inactive campaigns resume winning auctions.
- The label-smoothing recipe is not tied to the specific tree classifier; the paper states it applies to any bucket-classification method with one-hot labels.
- Tail prediction improves because the proxy-regression side handles large counts that the wide final bucket would otherwise over- or under-estimate.
Reading between the lines
- If the narrow-range PCOC property turns out to be universal across platforms, the proxy-label trick could be reused for any delayed-feedback count where a biased online estimator exists.
- The soft-label smoothing scheme could be tested on other integer-valued long-tail regression tasks, such as watch-time or purchase-count prediction, where boundary discontinuities hurt hard-label classifiers.
- A natural stress test is to hold out product categories with unusually high or low PCOC spread; if VRMP degrades there, the MoE gate could be extended to use PCOC spread as an input feature.
- The paper's five-day online test leaves open whether the gains persist over a longer horizon; measuring compliance rate and revenue drift over several weeks would be a direct follow-up.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper addresses the problem of predicting the number of long-delayed ad conversions at the campaign level for use in automated bidding. The proposed LDACP model combines two modules: BCMS, which converts regression into a tree-structured bucket classification with non-normalized soft labels and label smoothing, and VRMP, which regresses the ratio PCOC = z/y (aggregated pCTCVR over actual conversions) and converts the prediction back to a conversion count. The two predictions are fused by a learned Mixture-of-Experts gate. The authors report offline experiments on a 2.7M-sample Kuai-AD dataset showing consistent improvements over six baselines (MAPE 0.2228 vs. 0.2914 for the best baseline; CR 62.32% vs. 53.80%), an ablation study attributing large gains to both modules, and an online A/B test on Kuaishou reporting a 2.29% compliance-rate improvement, 11.06% revenue increase, and 8.68% conversion increase.
Significance. If the reported results hold, the paper makes a useful industrial contribution: it formulates a practically important problem, provides a clean decomposition of the long-tail and label-discontinuity difficulties, and validates the method on a large real dataset and in an online deployment. The offline evaluation is substantial and the ablations are informative. I agree with the reader that the VRMP proxy is not circular: PCOC is a reparameterization of the target y, not a self-referential fitted constant. That said, the central offline claims rest on metrics that are not well-defined for y=0 samples, and the online test is reported without any statistical uncertainty. Both issues need to be resolved before the headline numbers can be taken at face value.
major comments (4)
- [Section 5.1.2, Eq. (19); Section 3, Table 2; Section 4.3, Eqs. (12) and (17)] The label space includes y=0 (Table 2 reports minimum conversions = 0), but the evaluation metrics CR in Eq. (19), MAPE in Section 5.1.2, and the MoE loss in Eq. (17) all divide by y. The paper does not state whether y=0 samples are excluded, assigned a special value, or handled by clipping. If they are dropped, the reported MAPE and CR describe only campaigns with at least one conversion, which is not the population most relevant to the bidding system: inactive campaigns with zero or very few tracked conversions are exactly where the predicted count is needed. If they are kept, the numerical results depend on an undisclosed convention and are not reproducible. This is load-bearing because Tables 3 and 4, including the headline MAPE 0.2228 and CR 62.32%, are computed from these metrics.
- [Section 4.3, Eq. (12); Figure 2b; Table 4] The core premise of VRMP is that PCOC has a narrow value range and no long tail (Section 4.3, Figure 2b). This property is in part manufactured by the definition in Eq. (12), which sets PCOC=1 for all y=0 samples even though z/y is undefined there. Without reporting the fraction of y=0 samples and the PCOC distribution conditional on y>0, Figure 2b cannot be read as evidence of a transferable distributional property. Since VRMP is credited with the largest ablation gain (CR drops by 9.42% when removed, Table 4), the authors should provide a more careful distributional analysis, including the zero-inflation rate, and state explicitly how the proxy is defined for zero-label samples in both training and evaluation.
- [Section 5.3, Table 5] The online A/B test is reported only as point estimates: the experimental group improves CR by 2.29% overall, with daily improvements ranging from 0.59 to 4.66 percentage points. No confidence intervals, p-values, number of campaigns, or traffic volumes are given, so the reader cannot assess whether the observed differences are statistically significant. The same applies to the revenue increase of 11.06% and the conversion increase of 8.68%. Given the commercial importance of the claim, the authors should report at least campaign-level variance and a significance test, or clearly label the result as a directional observation.
- [Section 5.1.1; Appendix A] The label window of three days is chosen without sensitivity analysis, and the conversion-delay statistics in Appendix A show that the p90 delay exceeds 2,770 minutes for several campaign types, so a three-day window still censors a non-negligible tail. Since all offline metrics and the downstream bidding signal depend on this label definition, the authors should either justify the window with data or provide results for alternative windows (e.g., one, two, four, and seven days).
minor comments (6)
- [Section 5.1.2, Eq. (19)] There is a typographical issue in Eq. (19): the summation is written as "Y∑︁ y", which should presumably be a standard sum over all labels y in the test set.
- [Section 4.3, Eq. (15)] The conversion from predicted PCOC to predicted conversion count divides by \hat{PCOC}, but the paper does not describe how zero or negative predictions of PCOC are handled; MAE regression can in principle produce such values, and the resulting division would be undefined or nonsensical.
- [Section 4.2.2, Eq. (9) and Table 1] The symbol e_i is used for the expectation value of a leaf node, but e_{i->j} is already used for an edge in Table 1; using two different meanings for e in the same paper is confusing and should be resolved by renaming one of them.
- [Section 5.1.1 and Section 4.3] The paper does not report the fraction of y=0 samples in Kuai-AD; this fraction is important both for interpreting the PCOC distribution in Figure 2b and for assessing how much of the reported CR/MAPE is determined by the convention for zero labels.
- [Section 5.3 and Section 4.4] The online deployment clips the predicted conversion count to be not less than the real-time tracked count, but the paper does not state whether this same clipping is applied to the offline predictions and to the MoE loss in Eq. (17); the offline and online settings should be aligned.
- [Section 5.1.3 and Eq. (18)] The hyperparameters alpha and beta in Eq. (18), as well as the smoothing temperature 10 in Eq. (21), are fixed empirically to 1 and 10, respectively, but no sensitivity study is reported; a short sensitivity analysis would increase confidence in the robustness of the method.
Circularity Check
No significant circularity: the VRMP proxy label is a learned ratio reparameterization, and the only self-citation (TPM) is code-backed and used as an empirical baseline.
full rationale
The derivation chain is self-contained. VRMP labels campaigns by PCOC = z/y (Eq. 12) and reconstructs predictions as y_g = z/PCOC_hat (Eq. 15); this is a bijective reparameterization of the target y given z, not a tautology, because PCOC_hat is learned from features x and z under the MAE loss (Eq. 14) and must generalize to held-out labels. BCMS and the MoE similarly minimize label-dependent losses (Eqs. 5, 17, 18) rather than returning fitted constants, so the reported offline gains (Table 3) and ablation gains (Table 4) are empirical, not by-construction. The only overlapping-author citation is TPM [14], used as the BCMS backbone and as a baseline; it is cited for its implementation ('we set the tree height to 7... using the implementation provided in the original paper') and is directly compared against in Table 3, so it is independent, code-reproduced support and does not import an unverified uniqueness claim. A caveat that is not circularity: with min conversions = 0 (Table 2), Eq. 12 sets PCOC=1 and Eqs. 17 and 19 divide by y, so CR/MAPE for zero-conversion samples depend on an undisclosed convention; this is a correctness/reproducibility risk, not self-reference.
Assumptions & free parameters
free parameters (5)
- alpha and beta in total loss =
1
- Smoothing temperature in h(x)=e^{-10x} =
10
- Distance function psi(y,m)=|y-m|/(y+epsilon) =
not specified (epsilon small)
- Tree height / number of leaf nodes =
64 (7 levels)
- Conversion delay window =
3 days
assumptions (4)
- domain assumption PCOC of the ranking model has a narrow value range and does not exhibit a long-tail distribution
- domain assumption Equal-frequency bucketing on integer long-tail labels puts many samples near bucket boundaries
- ad hoc to paper The soft-label mapping h(psi) preserves ordering and yields smooth gradients
- domain assumption The aggregated pCTCVR z is a useful input feature and its prediction bias is stable
Cite this review
Pith. "Pith review of LDACP: Long-Delayed Ad Conversions Prediction Model for Bidding Strategy." pith.science (2026). https://pith.science/paper/STWTRK6J
@misc{pith2026241116095,
author = {Pith},
title = {Pith review of: LDACP: Long-Delayed Ad Conversions Prediction Model for Bidding Strategy},
year = {2026},
howpublished = {\url{https://pith.science/paper/STWTRK6J}},
note = {Machine review of arXiv:2411.16095}
}
read the original abstract
In online advertising, once an ad campaign is deployed, the automated bidding system dynamically adjusts the bidding strategy to optimize Cost Per Action (CPA) based on the number of ad conversions. For ads with a long conversion delay, relying solely on the real-time tracked conversion number as a signal for bidding strategy can significantly overestimate the current CPA, leading to conservative bidding strategies. Therefore, it is crucial to predict the number of long-delayed conversions. Nonetheless, it is challenging to predict ad conversion numbers through traditional regression methods due to the wide range of ad conversion numbers. Previous regression works have addressed this challenge by transforming regression problems into bucket classification problems, achieving success in various scenarios. However, specific challenges arise when predicting the number of ad conversions: 1) The integer nature of ad conversion numbers exacerbates the discontinuity issue in one-hot hard labels; 2) The long-tail distribution of ad conversion numbers complicates tail data prediction. In this paper, we propose the Long-Delayed Ad Conversions Prediction model for bidding strategy (LDACP), which consists of two sub-modules. To alleviate the issue of discontinuity in one-hot hard labels, the Bucket Classification Module with label Smoothing method (BCMS) converts one-hot hard labels into non-normalized soft labels, then fits these soft labels by minimizing classification loss and regression loss. To address the challenge of predicting tail data, the Value Regression Module with Proxy labels (VRMP) uses the prediction bias of aggregated pCTCVR as proxy labels. Finally, a Mixture of Experts (MoE) structure integrates the predictions from BCMS and VRMP to obtain the final predicted ad conversion number.
Figures
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Reference graph
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Reviewed August 12, 2026 · model on record in the stance chip above.
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