• Title, Summary, Keyword: case control

Search Result 9,735, Processing Time 0.065 seconds

The Effect of Increasing Control-to-case Ratio on Statistical Power in a Simulated Case-control SNP Association Study

  • Kang, Moon-Su;Choi, Sun-Hee;Koh, In-Song
    • Genomics & Informatics
    • /
    • v.7 no.3
    • /
    • pp.148-151
    • /
    • 2009
  • Generally, larger sample size leads to a greater statistical power to detect a significant difference. We may increase the sample size for both case and control in order to obtain greater power. However, it is often the case that increasing sample size for case is not feasible for a variety of reasons. In order to look at change in power as the ratio of control to case varies (1:1 to 4:1), we conduct association tests with simulated data generated by PLINK. The simulated data consist of 50 disease SNPs and 300 non-disease SNPs and we compute powers for disease SNPs. Genetic Power Calculator was used for computing powers with varying the ratio of control to case (1:1, 2:1, 3:1, 4:1). In this study, we show that gains in statistical power resulting from increasing the ratio of control to case are substantial for the simulated data. Similar results might be expected for real data.

A review of analysis methods for secondary outcomes in case-control studies

  • Schifano, Elizabeth D.
    • Communications for Statistical Applications and Methods
    • /
    • v.26 no.2
    • /
    • pp.103-129
    • /
    • 2019
  • The main goal of a case-control study is to learn the association between various risk factors and a primary outcome (e.g., disease status). Particularly recently, it is also quite common to perform secondary analyses of the case-control data in order to understand certain associations between the risk factors of the primary outcome. It has been repeatedly documented with case-control data, association studies of the risk factors that ignore the case-control sampling scheme can produce highly biased estimates of the population effects. In this article, we review the issues of the naive secondary analyses that do not account for the biased sampling scheme, and also the various methods that have been proposed to account for the case-control ascertainment. We additionally compare the results of many of the discussed methods in an example examining the association of a particular genetic variant with smoking behavior, where the data were obtained from a lung cancer case-control study.

Adjusting sampling bias in case-control genetic association studies

  • Seo, Geum Chu;Park, Taesung
    • Journal of the Korean Data and Information Science Society
    • /
    • v.25 no.5
    • /
    • pp.1127-1135
    • /
    • 2014
  • Genome-wide association studies (GWAS) are designed to discover genetic variants such as single nucleotide polymorphisms (SNPs) that are associated with human complex traits. Although there is an increasing interest in the application of GWAS methodologies to population-based cohorts, many published GWAS have adopted a case-control design, which raise an issue related to a sampling bias of both case and control samples. Because of unequal selection probabilities between cases and controls, the samples are not representative of the population that they are purported to represent. Therefore, non-random sampling in case-control study can potentially lead to inconsistent and biased estimates of SNP-trait associations. In this paper, we proposed inverse-probability of sampling weights based on disease prevalence to eliminate a case-control sampling bias in estimation and testing for association between SNPs and quantitative traits. We apply the proposed method to a data from the Korea Association Resource project and show that the standard estimators applied to the weighted data yield unbiased estimates.

Sample Size and Power Estimation in Case-Control Genetic Association Studies

  • Ahn Chul
    • Genomics & Informatics
    • /
    • v.4 no.2
    • /
    • pp.51-56
    • /
    • 2006
  • In planning a genetic association study, it is necessary to determine the number of samples to be collected for the study in order to achieve sufficient power to detect the hypothesized effect. The case-control design is increasingly used for genetic association studies due to the simplicity of its design. We review the methods for the sample size and power calculations in case-control genetic association studies between a marker locus and a disease phenotype.

Worst-case optimal feedback control policy for a remote electrical drive system with time-delay

  • Gao, Yu;Zhang, Zheng;Lee, Chang-Goo;Chong, Kil-To
    • Proceedings of the KIEE Conference
    • /
    • /
    • pp.92-94
    • /
    • 2007
  • This paper considers an optimal control problem for a remote control to an electrical drive system with a DC motor. Since it is a linear control system with time-delay subject to unknown but bounded disturbance, we construct a worst-case feedback control policy. This policy can guarantee that, for all admissible uncertain disturbances, the real system state should be in a prescribed neighborhood of a desired value, and the cost functional takes the best guarantee value. The worst-case feedback control policy is allowed to be corrected at one correction point between the initial to the final time, which is equivalent to solving a 1-level min-max problem. Since the min-max problem at the stage does not yield a simple analytical solution, we consider an approximate control policy, which is equivalent and can be solved explicitly m the numerical experiments.

  • PDF

Epstein-Barr Virus and Gastric Cancer Risk: A Meta-analysis With Meta-regression of Case-control Studies

  • Bae, Jong-Myon;Kim, Eun Hee
    • Journal of Preventive Medicine and Public Health
    • /
    • v.49 no.2
    • /
    • pp.97-107
    • /
    • 2016
  • Objectives: Research on how the risk of gastric cancer increases with Epstein-Barr virus (EBV) infection is lacking. In a systematic review that investigated studies published until September 2014, the authors did not calculate the summary odds ratio (SOR) due to heterogeneity across studies. Therefore, we include here additional studies published until October 2015 and conduct a meta-analysis with meta-regression that controls for the heterogeneity among studies. Methods: Using the studies selected in the previously published systematic review, we formulated lists of references, cited articles, and related articles provided by PubMed. From the lists, only case-control studies that detected EBV in tissue samples were selected. In order to control for the heterogeneity among studies, subgroup analysis and meta-regression were performed. Results: In the 33 case-control results with adjacent non-cancer tissue, the total number of test samples in the case and control groups was 5280 and 4962, respectively. In the 14 case-control results with normal tissue, the total number of test samples in case and control groups was 1393 and 945, respectively. Upon meta-regression, the type of control tissue was found to be a statistically significant variable with regard to heterogeneity. When the control tissue was normal tissue of healthy individuals, the SOR was 3.41 (95% CI, 1.78 to 6.51; I-squared, 65.5%). Conclusions: The results of the present study support the argument that EBV infection increases the risk of gastric cancer. In the future, age-matched and sex-matched case-control studies should be conducted.

The Visual Performance Evaluation of the Work planes with the Automated blind Control in Small Office Spaces

  • Park, Doo-Yong;Yoon, Kap-Chun;Kim, Kang-Soo
    • KIEAE Journal
    • /
    • v.14 no.1
    • /
    • pp.15-22
    • /
    • 2014
  • Among the various building envelope elements, the glass area takes up the largest portion in the office building design. However, a large area of glass can cause problems such as excessive solar radiation, thermal comfort, and glare. Thus it is important to install the glass area to an appropriate level, and control solar radiation and inflow of daylight with blind devices. This study aims to improve the visual performance of the work plane through the automatic control of the venetian blinds. A total of eight kinds of control strategies were chosen; Case 1 does not control the blinds, Case 2 with the blind slats fixed at the angle of 0 degree, Case 3 to 6 using the existing blind control programs, and Case 7 and 8 with improved blind control. Case 3 with 90 degrees had the best energy performance, but the average indoor illuminance was 113lux, which is below the standards. Cases 4 and 5 showed higher levels of interior daylight illuminance with the average of 281lux and 403lux respectively. However, the fixed angles may have difficulties controlling excessive direct sunlight coming into the room and may cause glare. Cases 6 and 7 used sun tracking angle control and cut-off angle control, and the average interior illuminance was measured 250lux and 385lux respectively. Case 8 used the cut-off angle control in an hourly manner, satisfying the standard illuminance of 400lux with an average interior illuminance of 561lux. It was evaluated to be the best method to control direct solar radiation and to guarantee proper level of interior illumination.

Study of Advanced Control for Chemical Process Using the Commercial Package PCTP Based on Model Predictive Control Algorithm (모델예측제어기반 상용 Package PCTP를 이용한 화학공정의 제어 고도화 연구)

  • Park, Jun-Ho;Park, Ho-Cheol;Lee, Moon-Yong
    • Journal of Institute of Control, Robotics and Systems
    • /
    • v.13 no.11
    • /
    • pp.1128-1136
    • /
    • 2007
  • This paper presents an application study of a model predictive control based commercial package PCTP to real chemical processes. The first case study concerns a product purity control of a splitter process which distillates styrene from undesired component ethyl-benzene produced from ethyl-benzene dehydrogenation reaction. The second case study is about a temperature control of ethyl-benzene dehydrogenation reactor and an excess oxygen control of the fired heater. Optimum control structure for MPC application is developed for each case study. The application results show a significant improvement in control performance and stability.

Sample Size and Statistical Power Calculation in Genetic Association Studies

  • Hong, Eun-Pyo;Park, Ji-Wan
    • Genomics & Informatics
    • /
    • v.10 no.2
    • /
    • pp.117-122
    • /
    • 2012
  • A sample size with sufficient statistical power is critical to the success of genetic association studies to detect causal genes of human complex diseases. Genome-wide association studies require much larger sample sizes to achieve an adequate statistical power. We estimated the statistical power with increasing numbers of markers analyzed and compared the sample sizes that were required in case-control studies and case-parent studies. We computed the effective sample size and statistical power using Genetic Power Calculator. An analysis using a larger number of markers requires a larger sample size. Testing a single-nucleotide polymorphism (SNP) marker requires 248 cases, while testing 500,000 SNPs and 1 million markers requires 1,206 cases and 1,255 cases, respectively, under the assumption of an odds ratio of 2, 5% disease prevalence, 5% minor allele frequency, complete linkage disequilibrium (LD), 1:1 case/control ratio, and a 5% error rate in an allelic test. Under a dominant model, a smaller sample size is required to achieve 80% power than other genetic models. We found that a much lower sample size was required with a strong effect size, common SNP, and increased LD. In addition, studying a common disease in a case-control study of a 1:4 case-control ratio is one way to achieve higher statistical power. We also found that case-parent studies require more samples than case-control studies. Although we have not covered all plausible cases in study design, the estimates of sample size and statistical power computed under various assumptions in this study may be useful to determine the sample size in designing a population-based genetic association study.

Adaptive MR damper cable control system based on piezoelectric power harvesting

  • Guan, Xinchun;Huang, Yonghu;Li, Hui;Ou, Jinping
    • Smart Structures and Systems
    • /
    • v.10 no.1
    • /
    • pp.33-46
    • /
    • 2012
  • To reduce the vibration of cable-stayed bridges, conventional magnetorheological (MR) damper control system (CMRDS), with separate power supply, sensors and controllers, is widely investigated. In this paper, to improve the reliability and performance of the control system, one adaptive MR damper control system (AMRDS) consisting of MR damper and piezoelectric energy harvester (PEH) is proposed. According to piezoelectric effect, PEH can produce energy for powering MR damper. The energy is proportional to the product of the cable displacement and velocity. Due to the damping force changing with the energy, the new system can be adjustable to reduce the cable vibration. Compared with CMRDS, the new system is structurally simplified, replacing external sensor, power supply and controller with PEH. In the paper, taking the N26 cable of Shandong Binzhou Yellow River Bridge as example, the design method for the whole AMRDS is given, and simple formulas for PEH are derived. To verify the effectiveness of the proposed adaptive control system, the performance is compared with active control case and simple Bang-Bang semi-active control case. It is shown that AMRDS is better than simple Bang-Bang semi-active control case, and still needed to be improved in comparison with active control case.