An IPW-based Unbiased Ranking Metric in Two-sided Markets

In modern recommendation systems, unbiased learning-to-rank (LTR) is crucial for prioritizing items from biased implicit user feedback, such as click data. Several techniques, such as Inverse Propensity Weighting (IPW), have been proposed for single-sided markets. However, less attention has been paid to two-sided markets, such as job platforms or dating services, where successful conversions require matching preferences from both users. This paper addresses the complex interaction of biases between users in two-sided markets and proposes a tailored LTR approach. We first present a formulation of feedback mechanisms in two-sided matching platforms and point out that their implicit feedback may include position bias from both user groups. On the basis of this observation, we extend the IPW estimator and propose a new estimator, named two-sided IPW, to address the position bases in two-sided markets. We prove that the proposed estimator satisfies the unbiasedness for the ground-truth ranking metric. We conducted numerical experiments on real-world two-sided platforms and demonstrated the effectiveness of our proposed method in terms of both precision and robustness. Our experiments showed that our method outperformed baselines especially when handling rare items, which are less frequently observed in the training data

S-1 plus leucovorin and oxaliplatin versus S-1 plus cisplatin as first-line therapy in patients with advanced gastric cancer (SOLAR): a randomised, open-label, phase 3 trial

Background S-1 plus leucovorin and oxaliplatin showed promising efficacy for treatment of advanced gastric cancer in a randomised phase 2 study. We aimed to evaluate the efficacy and safety of oral TAS-118 (S-1 plus leucovorin) and oxaliplatin versus S-1 plus cisplatin in patients with advanced gastric cancer. Methods We did a randomised, open-label, phase 3 trial in 62 centres across Japan and South Korea. Patients aged 20 years or older, with a histologically confirmed advanced gastric cancer with negative or unknown HER2 status, with Eastern Cooperative Oncology Group performance status of 0 or 1, measurable or evaluable metastatic lesions, and no previous treatment were randomly assigned (1:1) via an interactive web response system using the minimisation method, stratified by performance status, presence of a measurable lesion, and country, to receive TAS-118 (S-140-60 mg and leucovorin 25 mg orally twice daily for 7 days) plus oxaliplatin (85 mg/m(2) intravenously on day 1) every 2 weeks, or S-1 (40-60 mg orally twice daily) for 21 days plus cisplatin (60 mg/m(2) intravenously on day 1 or 8) every 5 weeks. The primary endpoint was overall survival in patients who had advanced gastric cancer with measurable or evaluable metastatic lesions and who received the study drug. Safety was assessed in all patients who received the study drug. This study was registered at ClinicalTrials.gov, NCT02322593. Findings Between Jan 28,2015, and Dec 5,2016,711 patients were randomised to TAS-118 plus oxaliplatin (n=356) or S-1 plus cisplatin (n=355). 11 untreated patients and 19 ineligible patients were excluded from the primary analysis (TAS-118 plus oxaliplatin group n=347, S-1 plus cisplatin group n=334) following recommendation from the independent data monitoring committee. After median follow-up of 26.0 months (IQR 22.0-32.8), median overall survival was 16.0 months (95% CI 13.8-18.3) in the TAS-118 plus oxaliplatin group and 15.1 months (95% CI 13.6-16.4) in the S-1 plus cisplatin group (hazard ratio 0.83, 95% CI 0.69-0.99; p=0.039). The most common grade 3 or higher adverse events in the 352 patients in the TAS-118 plus oxaliplatin group and the 348 patients in the S-1 plus cisplatin group were anaemia (56 [16%] vs 64 [18%]), neutropenia (54 [15%] vs 88 [25%]), decreased appetite (53 [15%] vs 46 [13%]), diarrhoea (33 [9%] vs 15 [4%]), and peripheral sensory neuropathy (30 [9%] vs one [<1%]). Serious adverse events were observed in 155 (44%) of 352 patients in the TAS-118 plus oxaliplatin group and 159 (46%) of 348 patients in the S-1 plus cisplatin group. Two treatment-related deaths occurred in the TAS-118 plus oxaliplatin group (pulmonary tuberculosis and viral pneumonia). Interpretation TAS-118 plus oxaliplatin showed a clinically meaningful improvement in efficacy compared with S-1 plus cisplatin, and could be considered a new first-line treatment option for advanced gastric cancer in Asian patients. Copyright (C) 2020 Elsevier Ltd. All rights reserved