Hayashi, Kenichi



Faculty of Science and Technology, Department of Mathematics (Yagami)


Associate Professor


Research Areas 【 Display / hide

  • Informatics / Statistical science


Books 【 Display / hide

  • Rで学ぶ統計的データ解析

    林 賢一, 講談社サイエンティフィク, 2020.11,  Page: 352

  • Machine Learning: The Art and Science of Algorithms that Make Sense of Data

    竹村彰通(監訳),田中研太郎,小林景,兵頭昌,片山翔太,山本倫生,吉田拓真,林賢一,松井秀俊,小泉和之,永井勇, 朝倉書店, 2017.04

    Scope: 7章

Papers 【 Display / hide

  • Model Selection with Missing Data Embedded in Missing-at-Random Data

    Takai K., Hayashi K.

    Stats (Stats)  6 ( 2 ) 495 - 505 2023.06

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    When models are built with missing data, an information criterion is needed to select the best model among the various candidates. Using a conventional information criterion for missing data may lead to the selection of the wrong model when data are not missing at random. Conventional information criteria implicitly assume that any subset of missing-at-random data is also missing at random, and thus the maximum likelihood estimator is assumed to be consistent; that is, it is assumed that the estimator will converge to the true value. However, this assumption may not be practical. In this paper, we develop an information criterion that works even for not-missing-at-random data, so long as the largest missing data set is missing at random. Simulations are performed to show the superiority of the proposed information criterion over conventional criteria.

  • An Accelerated Failure Time Cure Model with Shifted Gamma Frailty and Its Application to Epidemiological Research

    Aida H., Hayashi K., Takeuchi A., Sugiyama D., Okamura T.

    Healthcare (Switzerland) (Healthcare (Switzerland))  10 ( 8 )  2022.08

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    Survival analysis is a set of methods for statistical inference concerning the time until the occurrence of an event. One of the main objectives of survival analysis is to evaluate the effects of different covariates on event time. Although the proportional hazards model is widely used in survival analysis, it assumes that the ratio of the hazard functions is constant over time. This assumption is likely to be violated in practice, leading to erroneous inferences and inappropriate conclusions. The accelerated failure time model is an alternative to the proportional hazards model that does not require such a strong assumption. Moreover, it is sometimes plausible to consider the existence of cured patients or long-term survivors. The survival regression models in such contexts are referred to as cure models. In this study, we consider the accelerated failure time cure model with frailty for uncured patients. Frailty is a latent random variable representing patients’ characteristics that cannot be described by observed covariates. This enables us to flexibly account for individual heterogeneities. Our proposed model assumes a shifted gamma distribution for frailty to represent uncured patients’ heterogeneities. We construct an estimation algorithm for the proposed model, and evaluate its performance via numerical simulations. Furthermore, as an application of the proposed model, we use a real dataset, Specific Health Checkups, concerning the onset of hypertension. Results from a model comparison suggest that the proposed model is superior to existing alternatives.

  • Pulmonary vein isolation alone vs. more extensive ablation with defragmentation and linear ablation of persistent atrial fibrillation: the EARNEST-PVI trial

    Inoue K., Hikoso S., Masuda M., Furukawa Y., Hirata A., Egami Y., Watanabe T., Minamiguchi H., Miyoshi M., Tanaka N., Oka T., Okada M., Kanda T., Matsuda Y., Kawasaki M., Hayashi K., Kitamura T., Dohi T., Sunaga A., Mizuno H., Nakatani D., Sakata Y.

    Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology (Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology)  23 ( 4 ) 565 - 574 2021.04

    ISSN  10995129

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    AIMS: Previous studies could not demonstrate any benefit of more intensive ablation in addition to pulmonary vein isolation (PVI) including complex fractionated atrial electrogram (CFAE) and linear ablation for recurrence in the initial catheter ablation of persistent atrial fibrillation (AF). This study aimed to establish the non-inferiority of PVI alone to PVI plus these additional ablation strategies. METHODS AND RESULTS: Patients with persistent AF who underwent an initial catheter ablation (n = 512, long-standing persistent AF; 128 cases) were randomly assigned in a 1:1 ratio to either PVI alone (PVI-alone group) or PVI plus CFAE and/or linear ablation (PVI-plus group). After excluding 15 cases who did not receive procedures, we analysed 249 and 248 patients, respectively. The primary endpoint was recurrence of AF, atrial flutter, and/or atrial tachycardia, and the non-inferior margin was set at a hazard ratio of 1.43. In the PVI-plus group, 85.1% of patients had linear ablation and 15.3% CFAE ablation. After 12 months, freedom from the primary endpoint occurred in 71.3% of patients in the PVI-alone group and in 78.3% in the PVI-plus group [hazard ratio = 1.56 (95% confidence interval: 1.10-2.24), non-inferior P = 0.3062]. The procedure-related complication rates were 2.0% in the PVI-alone group and 3.6% in the PVI-plus group (P = 0.199). CONCLUSION: This randomized trial did not establish the non-inferiority of PVI alone to PVI plus linear ablation or CFAE ablation in patients with persistent AF, but implied that the PVI plus strategy was promising to improve the clinical efficacy (NCT03514693).

  • A nationwide randomized, double-blind, placebo-controlled physicians’ trial of loxoprofen for the treatment of fatigue, headache, and nausea after hangovers

    Hara M., Hayashi K., Kitamura T., Honda M., Tamaki M.

    Alcohol (Alcohol)  84   21 - 25 2020.05

    ISSN  07418329

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    Hangovers are associated with negative economic consequences due to decreased job performance or frequent visits to physicians. Thus, a new strategy for the alleviation of hangover-related symptoms is needed to avoid this detriment to society. The purpose of this nationwide randomized, double-blind, placebo-controlled physicians’ trial was to evaluate the efficacy of loxoprofen sodium for the alleviation of fatigue, headache, and nausea after hangover. A total of 229 participants were randomized to receive loxoprofen sodium (60 mg once orally) or placebo. The study was closed when the first 150 participants (n = 74 in the loxoprofen vs. n = 76 in the placebo groups) experienced hangovers. The primary endpoint was set as the difference in severity of general fatigue before and 3 h after taking the test drugs and was evaluated using a visual analogue scale. Secondary endpoints included difference in severity of headache, nausea, and incidence of adverse events. The study participants were 34 (interquartile range; 30–39) years old, 92.0% were men, and both groups were comparable for baseline characteristics. The alleviation of general fatigue did not differ statistically between the loxoprofen and placebo groups (24 [14–49] vs. 19 [9–35], p = 0.07). However, the alleviation of headache was statistically greater in the loxoprofen group (25 [10–50] vs. 10 [2–30], adjusted difference 14, 95% confidence interval 8–21, p < 0.001), whereas, there was no difference in nausea (7 [0–27] vs. 10 [0–24], p = 0.68). The incidence of adverse symptoms such as epigastric discomfort was also comparable between groups (2.7% vs. 3.9%, p = 0.25). Loxoprofen sodium was effective for relieving headaches after hangovers but did not alleviate general fatigue or nausea.

  • Effect of Extensive Ablation on Recurrence in Patients with Persistent Atrial Fibrillation Treated with Pulmonary Vein Isolation (EARNEST-PVI) trial: Design and rationale

    Dohi T., Nakatani D., Inoue K., Hikoso S., Oka T., Hayashi K., Masuda M., Furukawa Y., Kawasaki M., Egami Y., Kashiwase K., Hirata A., Watanabe T., Miyoshi M., Takeda T., Nakagawa A., Mizuno H., Minamiguchi H., Kitamura T., Suna S., Kojima T., Kida H., Bolrathanak O., Okuyama Y., Sakata Y.

    Journal of Cardiology (Journal of Cardiology)  74 ( 2 ) 164 - 168 2019.08

    ISSN  09145087

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    Background: Although extensive substrate modification in addition to pulmonary vein isolation (PVI) has been recommended in catheter ablation for persistent atrial fibrillation (AF), recent randomized controlled trials have not demonstrated efficacy of such additional ablations. Methods and study design: The Osaka Cardiovascular Conference will conduct a multicenter, randomized, open-label trial aiming to examine whether PVI alone is non-inferior to PVI plus additional ablation such as linear ablation and/or complex fractionated atrial electrogram ablation in patients with persistent AF. The primary outcome is recurrence of AF documented by scheduled or symptom-driven electrocardiogram tests during a 1-year follow-up period after the index ablation. The key secondary endpoints include all-cause death, occurrence of symptomatic stroke, complications related to the procedure, and quality of life assessment using the 36-item Short-Form Health Survey. The clinical impact of the presence or absence of AF trigger foci, and their origins in cases with them, on the results of catheter ablation will also be investigated as an exploratory endpoint. A total of 512 patients will be enrolled and followed up to 1 year. Conclusions: The EARNEST-PVI trial is a randomized controlled trial designed to assess whether PVI alone is non-inferior to extended substrate ablation for patients with persistent AF undergoing a first catheter ablation.

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Papers, etc., Registered in KOARA 【 Display / hide

Research Projects of Competitive Funds, etc. 【 Display / hide

  • 不均衡データに対する解析法の統合的理解と生存時間解析への発展的応用


    基盤研究(C), Principal investigator

  • 異質な集団を含むデータに対する統計的学習理論を用いたモデル開発と臨床医学への応用


    MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Principal investigator

  • A study on exploratory identification of responsive subgroups in complex survival event data


    MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (B), Principal investigator

Awards 【 Display / hide

  • 若手優秀発表賞

    2021.05, 日本計量生物学会

    Type of Award: Award from Japanese society, conference, symposium, etc.

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    2021年度計量生物学会年会 若手優秀発表賞(正会員の部)

  • 最優秀賞

    奥富航,林賢一, 2018.01, 第7回スポーツデータ解析コンペティション審査会, 第7回スポーツデータ解析コンペティション

    Type of Award: Other

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  • 論文賞

    2017.12, 日本分類学会, 日本分類学会

    Type of Award: Award from Japanese society, conference, symposium, etc.

  • 論文賞

    2015.05, 日本計算機統計学会, 日本計算機統計学会

    Type of Award: Award from Japanese society, conference, symposium, etc.


Courses Taught 【 Display / hide











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