• Asian-Australasian Journal of Animal Sciences
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• 제32권9호
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• pp.1349-1354
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• 2019

Objective: The objective of this study was to determine the best approach for handling missing records of first to successful insemination (FS) in Japanese Black heifers. Methods: Of a total of 2,367 records of heifers born between 2003 and 2015 used, 206 (8.7%) of open heifers were missing. Four penalty methods based on the number of inseminations were set as follows: C1, FS average according to the number of inseminations; C2, constant number of days, 359; C3, maximum number of FS days to each insemination; and C4, average of FS at the last insemination and FS of C2. C5 was generated by adding a constant number (21 d) to the highest number of FS days in each contemporary group. The bootstrap method was used to compare among the 5 methods in terms of bias, mean squared error (MSE) and coefficient of correlation between estimated breeding value (EBV) of non-censored data and censored data. Three percentages (5%, 10%, and 15%) were investigated using the random censoring scheme. The univariate animal model was used to conduct genetic analysis. Results: Heritability of FS in non-censored data was $0.012{\pm}0.016$, slightly lower than the average estimate from the five penalty methods. C1, C2, and C3 showed lower standard errors of estimated heritability but demonstrated inconsistent results for different percentages of missing records. C4 showed moderate standard errors but more stable ones for all percentages of the missing records, whereas C5 showed the highest standard errors compared with noncensored data. The MSE in C4 heritability was $0.633{\times}10^{-4}$, $0.879{\times}10^{-4}$, $0.876{\times}10^{-4}$ and $0.866{\times}10^{-4}$ for 5%, 8.7%, 10%, and 15%, respectively, of the missing records. Thus, C4 showed the lowest and the most stable MSE of heritability; the coefficient of correlation for EBV was 0.88; 0.93 and 0.90 for heifer, sire and dam, respectively. Conclusion: C4 demonstrated the highest positive correlation with the non-censored data set and was consistent within different percentages of the missing records. We concluded that C4 was the best penalty method for missing records due to the stable value of estimated parameters and the highest coefficient of correlation.

• Communications for Statistical Applications and Methods
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• 제24권2호
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• pp.143-154
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• 2017

A variable selection method based on probabilistic principal component analysis (PCA) using penalized likelihood method is proposed. The proposed method is a two-step variable reduction method. The first step is based on the probabilistic principal component idea to identify principle components. The penalty function is used to identify important variables in each component. We then build a model on the original data space instead of building on the rotated data space through latent variables (principal components) because the proposed method achieves the goal of dimension reduction through identifying important observed variables. Consequently, the proposed method is of more practical use. The proposed estimators perform as the oracle procedure and are root-n consistent with a proper choice of regularization parameters. The proposed method can be successfully applied to high-dimensional PCA problems with a relatively large portion of irrelevant variables included in the data set. It is straightforward to extend our likelihood method in handling problems with missing observations using EM algorithms. Further, it could be effectively applied in cases where some data vectors exhibit one or more missing values at random.

• 응용통계연구
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• 제26권5호
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• pp.697-712
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• 2013

다시점 자료 연구에서 일반화추정방정식은 가상관행렬을 잘못 가정하더라도 모수의 일치추정량을 도출하므로 많이 이용된다. 하지만, 결측 체계가 완전임의결측이 아닌 경우에는 편의추정량을 제공하고, 시간-종속적 공변량이 포함된 경우에는 가상관행렬에 따라 회귀계수 추정값이 다르게 도출될 수 있는 문제점이 있다. 결측 체계가 임의결측인 경우에 발생하는 문제를 해결하기 위해 가중 방법과 다중대체 방법을 사용하는 것이 제안되었다. 본 논문에서는 시간-종속적 공변량이 포함된 이분형 반복측정자료를 GEE를 이용하여 분석할 때 다양한 결측 체계에서 일반화추정방정식 방법, 가중 방법, 다중대체 방법의 회귀계수 추정에 대한 로버스트성과 정확성을 모의실험을 통하여 비교해 보았다. 세 가지 방법 모두에서 시간-종속적 공변량의 회귀계수가 시간-독립적 공변량의 회귀계수에 비해 가상관행렬에 따라 추정값의 차이가 크게 나타났다. 다른 두 방법에 비해 다중대체 방법이 가상관행렬의 형태에 대해 더 로버스트하고 편의도 작은 추정치를 도출하였다.

• 문화기술의 융합
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• 제8권6호
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• pp.899-904
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• 2022

본 세계적으로 출생률이 줄고 기대 수명이 늘어나 고령화 사회가 되어감에 따라 고령 인구의 건강 관리를 위한 시스템이 필요하다. 그 중 실내 건강 관리를 위한 스마트 홈 캐어 서비스를 위해서는 재실 여부 및 활동 유형에 관한 다양한 연구가 수행되고 있다. 본 논문에서는 스마트 홈 캐어 서비스를 위해 실내 온습도, CO2, 미세먼지 값과UWB 레이더 측위를 통해 재실 여부 뿐만 아니라 활동 유형을 분류하는 랜덤 포레스트 모델을 제안한다. 실험은 실내 온습도, CO2, 미세먼지를 측정하는 센서 3개와 UWB Radar 2개를 사용하여 2초 간격으로 실내 환경 및 재실자의 측위 데이터를 측정한다. 측정된 데이터는 이상치와 결측치를 보정 처리한 후 80%의 트레이닝 셋 데이터와 20%의 테스트 셋 데이터로 이분하며 랜덤 포레스트 모델을 적용하여 중요도 상위 변수 목록, 정확도, 민감도, 특이도, T1 스코어를 평가한다.

• Journal of the Korean Data and Information Science Society
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• 제15권4호
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• pp.993-1002
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• 2004

Imputation procedures such as fully efficient fractional imputation(FEFI) or multiple imputation(MI) can be used to construct complete contingency tables from samples with partially classified responses. Variances of FEFI estimators of population proportions are derived. Simulation results, when data are missing completely at random, reveal that FEFI provides more efficient estimates of population than either multiple imputation(MI) based on data augmentation or complete case analysis, but neither FEFI nor MI provides an improvement over complete-case(CC) analysis with respect to accuracy of estimation of some parameters for association between two variables like $\theta_{i+}\theta_{+i}-\theta_{ij}$ and log odds-ratio.

• 천문학회지
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• 제4권1호
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• pp.1-8
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• 1971

The average velocity, 330km/sec. of the high velocity stars with respect to the galactic center is obtained from the data used by Fricke on the assumption that the rotational velocity of the Local Standard of Rest is 250km/sec. Comparing this value with the escape velocity, 380km/sec, at the solar neighborhood which is calculated from Mestel's model of the Galaxy, it is shown that most of the high velocity stars are bound to the Galaxy and that their average apogalacticon is about 40 kpc from the galactic center. And the fact that stars with radial velocities larger than 63km/sec are missing in the direction of galactic rotation of L.S.R. is interpreted as the result partly of the random distribution of the directions of motion of the high velocity stars and partly of the observational errors.

• Journal of the Korean Data and Information Science Society
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• 제17권3호
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• pp.919-925
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• 2006

Maximum likelihood estimate(MLE) is obtained from the partial log-likelihood function for the cell probabilities of two way incomplete contingency tables proposed by Chen and Fienberg(1974). The partial log-likelihood function is modified by adding lagrangian multiplier that constraints can be incorporated with. Variances of MLE estimators of population proportions are derived from the matrix of second derivatives of the loglikelihood with respect to cell probabilities. Simulation results, when data are missing at random, reveal that Complete-case(CC) analysis produces biased estimates of joint probabilities under MAR and less efficient than either MLE or MI. MLE and MI provides consistent results under either the MAR situation. MLE provides more efficient estimates of population proportions than either multiple imputation(MI) based on data augmentation or complete case analysis. The standard errors of MLE from the proposed method using lagrangian multiplier are valid and have less variation than the standard errors from MI and CC.

• Journal of the Korean Data and Information Science Society
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• 제28권5호
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• pp.1077-1085
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• 2017

본 연구에서는 한국노동연구원의 "2015년 한국노동패널조사 (KLIPS)" 자료를 활용하여 국내 여성의 임금 결정요인을 분석하기 한다. 일반적으로 임금 자료는 랜덤 추출이 불가능하기 때문에 분석하기가 쉽지 않다. 표본 선택 편의 (sampling bias)가 있는 자료를 분석하는 방법으로 Heckman 표본 선택 모형이 가장 널리 알려져 있다. Heckman은 크게 두 가지 모형을 제안했는데, 그 중 하나는 최대 우도 방법을 이용하는 것이고, 다른 하나는 2단계 표본 선택 모형이다. 이 중 Heckman 2단계 표본 선택 모형은 주된 결과 모형 (outcome model)과 경제 활동 여부를 결정짓는 선택 모형 (selection model)을 포함한 모형으로써, 이 모형이 최대 우도 방법을 이용한 모형에 비해 이변수 오차의 정규분포 가정에 덜 민감하다고 알려져 있다. 그럼에도 불구하고 이변수 오차에 대한 정규 분포 가정은 꽤 강한 가정이라고 볼 수 있는데, 최근에 이 모형의 단점을 보완하는 모형으로 Marchenko와 Genton (2012)의Heckman 표본 선택 t 모형이 제시되었다. Heckman 2단계 모형과 Heckman 표본 선택 t 모형을 이용하여 국내 여성의 임금 결정 요인을 분석하고 비교하도록 한다.

• Smart Structures and Systems
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• 제25권3호
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• pp.369-384
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• 2020

A wavefield sparse reconstruction technique based on compressed sensing is developed in this work to dramatically reduce the number of measurements. Firstly, a severely underdetermined representation of guided wavefield at a snapshot is established in the spatial domain. Secondly, an optimal compressed sensing model of guided wavefield sparse reconstruction is established based on l₁-norm penalty, where a suite of discrete cosine functions is selected as the dictionary to promote the sparsity. The regular, random and jittered undersampling schemes are compared and selected as the undersampling matrix of compressed sensing. Thirdly, a gradient projection method is employed to solve the compressed sensing model of wavefield sparse reconstruction from highly incomplete measurements. Finally, experiments with different excitation frequencies are conducted on an aluminum plate to verify the effectiveness of the proposed sparse reconstruction method, where a scanning laser Doppler vibrometer as the true benchmark is used to measure the original wavefield in a given inspection region. Experiments demonstrate that the missing wavefield data can be accurately reconstructed from less than 12% of the original measurements; The reconstruction accuracy of the jittered undersampling scheme is slightly higher than that of the random undersampling scheme in high probability, but the regular undersampling scheme fails to reconstruct the wavefield image; A quantified mapping relationship between the sparsity ratio and the recovery error over a special interval is established with respect to statistical modeling and analysis.

• 전자공학회논문지CI
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• 제45권3호
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• pp.15-21
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• 2008

본 논문은 2단 샘플링을 통해 정확도는 줄지만 신속하게 연관규칙을 추출하는 새로운 마이닝 알고리즘을 제안한다. 직전 연구인 FAST(Finding Association by Sampling Technique) 기법은 빈발1항목만 최적샘플 형성과정에 적용하여 빈발2항목 및 그이상의 빈발항목을 샘플 추출에 반영하지 못하였다. 이 논문은 그러한 약점을 보완하여 트리밍 과정에서 손실항목과 오류항목의 비중을 동시에 고려하여 다수 빈발항목에 대한 마이닝의 정확성을 높였다. 대표적인 데이터 세트를 써서 실험한 결과 이전연구와 비교해서 동일한 품질하에서 새 알고리즘의 정확도가 향상됨을 확인하였다.