• Title/Summary/Keyword: adaptive designs

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Modified Adaptive Cluster Sampling Designs

  • Park, Jeong-Soo;Kim, Youn-Woo;Son, Chang-Kyoon
    • Communications for Statistical Applications and Methods
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    • v.14 no.1
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    • pp.57-69
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    • 2007
  • Adaptive cluster sampling design is known as a sampling method for rare clustered population. Three modified adaptive cluster sampling designs are proposed. The adjusted Hansen-Hurwitz estimator and the Horvitz-Thompson estimator are considered. Efficiency issue of the proposed sampling designs is discussed in a Monte-Carlo simulation study.

Estimating survival distributions for two-stage adaptive treatment strategies: A simulation study

  • Vilakati, Sifiso;Cortese, Giuliana;Dlamini, Thembelihle
    • Communications for Statistical Applications and Methods
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    • v.28 no.5
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    • pp.411-424
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    • 2021
  • Inference following two-stage adaptive designs (also known as two-stage randomization designs) with survival endpoints usually focuses on estimating and comparing survival distributions for the different treatment strategies. The aim is to identify the treatment strategy(ies) that leads to better survival of the patients. The objectives of this study were to assess the performance three commonly cited methods for estimating survival distributions in two-stage randomization designs. We review three non-parametric methods for estimating survival distributions in two-stage adaptive designs and compare their performance using simulation studies. The simulation studies show that the method based on the marginal mean model is badly affected by high censoring rates and response rate. The other two methods which are natural extensions of the Nelson-Aalen estimator and the Kaplan-Meier estimator have similar performance. These two methods yield survival estimates which have less bias and more precise than the marginal mean model even in cases of small sample sizes. The weighted versions of the Nelson-Aalen and the Kaplan-Meier estimators are less affected by high censoring rates and low response rates. The bias of the method based on the marginal mean model increases rapidly with increase in censoring rate compared to the other two methods. We apply the three methods to a leukemia clinical trial dataset and also compare the results.

The Designs of the Digital Minimum-Time Controller and the Digital Adaptive Controller Using Refererce Model (기준 모델을 이용한 디지털 최소-시간 제어기 및 디지털 적응 제어기의 설계)

  • 김종환;최계근
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.22 no.2
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    • pp.31-35
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    • 1985
  • This paper presents novel designs of a digital minimum-time controller and a digital adaptive controller using reference no del for single input-single out put linear time-invariant plants with known parameters. The proposed digital minimum-time controller which has a deadbeat response is designed to make the transfer function of this controller equal to that of reference model, and the proposed digital adaptive controller is designed by applying the adaptation method to the proposed digital minimum-time controller. The designs of these two controllers are very simple and easy, and all types of input signal with any reference models are controllable. These dffectivenesses have been demon-strated by computer simulations carried out for a third-order plant.

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Bayesian methods in clinical trials with applications to medical devices

  • Campbell, Gregory
    • Communications for Statistical Applications and Methods
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    • v.24 no.6
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    • pp.561-581
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    • 2017
  • Bayesian statistics can play a key role in the design and analysis of clinical trials and this has been demonstrated for medical device trials. By 1995 Bayesian statistics had been well developed and the revolution in computing powers and Markov chain Monte Carlo development made calculation of posterior distributions within computational reach. The Food and Drug Administration (FDA) initiative of Bayesian statistics in medical device clinical trials, which began almost 20 years ago, is reviewed in detail along with some of the key decisions that were made along the way. Both Bayesian hierarchical modeling using data from previous studies and Bayesian adaptive designs, usually with a non-informative prior, are discussed. The leveraging of prior study data has been accomplished through Bayesian hierarchical modeling. An enormous advantage of Bayesian adaptive designs is achieved when it is accompanied by modeling of the primary endpoint to produce the predictive posterior distribution. Simulations are crucial to providing the operating characteristics of the Bayesian design, especially for a complex adaptive design. The 2010 FDA Bayesian guidance for medical device trials addressed both approaches as well as exchangeability, Type I error, and sample size. Treatment response adaptive randomization using the famous extracorporeal membrane oxygenation example is discussed. An interesting real example of a Bayesian analysis using a failed trial with an interesting subgroup as prior information is presented. The implications of the likelihood principle are considered. A recent exciting area using Bayesian hierarchical modeling has been the pediatric extrapolation using adult data in clinical trials. Historical control information from previous trials is an underused area that lends itself easily to Bayesian methods. The future including recent trends, decision theoretic trials, Bayesian benefit-risk, virtual patients, and the appalling lack of penetration of Bayesian clinical trials in the medical literature are discussed.

The Necessity of Independent Data Monitoring Committee in Domestic Clinical Trials (현재 국내임상시험에서 독립적 자료모니터링위원회의 필요성)

  • Kang, Seung-Ho
    • The Korean Journal of Applied Statistics
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    • v.22 no.2
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    • pp.317-327
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    • 2009
  • In adaptive designs important components of clinical trials may be changed based on the results of interim analysis. Several international guidelines point out that such interim analysis should be performed by independent experts who do not participate in clinical trials when adaptive designs are used in therapeutic confirmatory clinical trials, and if not, it may cause bias. The international guidelines recommend the establishment of independent data monitoring committee for conducting interim analysis independently.

An adaptive control of servo motors for reducing the effect of cogging torques (코깅 토크의 영향 저감을 위한 서보 모터 적응제어)

  • 이수한;허상진
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.291-294
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    • 2004
  • Many researches have been focused on optimal designs of a pole shape in order to reduce cogging torques, which are generated between permanent magnets and slots. In this paper, an adaptive controller is proposed for reducing the effect of cogging torques in servo motors. The controller stabilizes the control system and shows an excellent trajectory tracking performance compared to the conventional PD controller.

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Spline-based Simplified Adaptive Observer Design for Nonlinear Systems (Spline을 이용한 비선형 시스템의 적응 관측기 설계)

  • Stoev, Julian;Baang, Dane;Cho, Jin-Young
    • Proceedings of the KIEE Conference
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    • 2005.10b
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    • pp.17-19
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    • 2005
  • In this paper, using B-splines as universial approximators, we have obtained a plant parametrization which permits the construction of an adaptive observer. The particular property of this parametrization is that the dynamic order of the filters in this design does not depend on the number of parameters in the plant parametrization. This appears to be a beneficial property especially because the number of such parameters tends to be very high for universial approximator based designs.

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Some Advantages of Spline-based Adaptive Observer Design for Nonlinear Systems (Spline을 이용한 비선형 시스템의 적응 관측기 설계)

  • Stoev, Julian;Bahng, Dane;Choi, Jin-Young
    • Proceedings of the KIEE Conference
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    • 2003.11b
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    • pp.331-334
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    • 2003
  • In this paper, using B-splines as universial approximators, we have obtained a plant parametrization which permits the construction of an adaptive observer. The particular property of this parametrization is that the dynamic order of the filters in this design does not depend on the number of parameters in the plant parametrization. This appears to be a beneficial property especially because the number of such parameters tends to be very high for universial approximator based designs.

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An Adaptive Control of Servo Motors for Reducing the Effect of cogging Torques (코깅 토크의 영향 저감을 위한 서보 모터 적응제어)

  • Lee Soo Han;Heo Sang Jin;Shin Kyu Hyeon
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.6 s.171
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    • pp.70-75
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    • 2005
  • Many researches have been focused on optimal designs of a pole shape in order to reduce cogging torques, which are generated between permanent magnets and slots. In this paper, an adaptive controller is proposed fur reducing the effect of cogging torques in servo motors. The controller stabilizes the control system and shows an excellent trajectory tracking performance compared to the conventional PD controller.

Sequential Designs for Complex Computer Experiments with an Application to a Nuclear Fusion Model (복잡한 전산실험을 위한 축차적 계획법과 핵 융합모형에의 응용)

  • Jeong Soo Park
    • The Korean Journal of Applied Statistics
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    • v.7 no.2
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    • pp.183-200
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    • 1994
  • Data-adaptive sequential suboptimal designs for very complex computer simulation codes are considered based on a spatial prediction model. These designs are constructed for two simulators of the computational nuclear fusion devices model. The difficulty of constructing the optimal designs due to the irregular design region, and its alternatives are also discussed with some computational algorithms for obtaining the designs.

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