• Journal of the Korean Statistical Society
• /
• 제26권3호
• /
• pp.383-395
• /
• 1997

This paper proves that the standard bootstrap approximation for the least absolute deviation (LAD) estimate of .beta. in AR(1) processes with infinite variance error terms is asymptotically valid in probability when the bootstrap resample size is much smaller than the original sample size. The theoretical validity results are supported by simulation studies.

• Journal of the Korean Data and Information Science Society
• /
• 제16권4호
• /
• pp.1079-1086
• /
• 2005

Most discussions of single imputation methods and the EM algorithm concern point estimation of population quantities with missing values. A second concern is how to get standard errors of the point estimates obtained from the filled-in data by single imputation methods and EM algorithm. Now we focus on how to estimate standard errors with incorporating the additional uncertainty due to nonresponse. There are some approaches to account for the additional uncertainty. The general two possible approaches are considered. One is the jackknife method of resampling methods. The other is multiple imputation(MI). These two approaches are reviewed and compared through simulation studies.

• Smart Structures and Systems
• /
• 제19권2호
• /
• pp.151-161
• /
• 2017

A new method is developed to estimate road profile in order to estimate IRI based on the ASTM standard. This method utilizes an accelerometer and a Dynamic Tire Pressure Sensor (DTPS) to estimate road roughness. The accelerometer measures the vertical axle acceleration. The DTPS, which is mounted on the tire's valve stem, measures dynamic pressure inside the tire while driving. Calibrated transfer functions are used to estimate road profile using the signals from the two sensors. A field test was conducted on roads with different quality conditions in the city of Brockton, MA. The IRI values estimated with this new method match the actual road conditions measured with Pavement Condition Index (PCI) based on the ASTM standard, images taken from an onboard camera and passengers' perceptions. IRI has negative correlation with PCI in general since they have overlapping features. Compared to the current method of IRI measurement, the advantage of this method is that a) the cost is reduced; b) more space is saved; c) more time is saved; and d) mounting the two sensors are universally compatible to most cars and vans. Therefore, this method has the potential to provide continuous and global monitoring the health of roadways.

• 대한음성학회지:말소리
• /
• 제51호
• /
• pp.17-37
• /
• 2004

The purpose of this dissertation is to make the general korean speakers to learn the standard pronunciations. But it is in existence that the obstructions of the command of the standard pronunciations. They are the mistake in the education course on the korean pronunciations, the teacher's capability and the mass communications's duplicity. To overcome this obstructions, we must concentrate our efforts on the propagation of the standard pronunciations. To propagate of the standard pronunciations we can take a several method. These are the presentation of the pronunciation mistakes, audio-visual teaching, the presentation of the pronunciation principles and the use of the korean dictionary. The standard pronunciations are different from the pronunciations of the general korean speakers in many respects. So we can't make an accurate estimate of the pronunciation's changes. No one knows what will happen in the future about the korean pronunciations. But we must teach the standard pronunciations to the general korean speakers. The standard pronunciations are offically valid in the present time.

• 대한가정학회지
• /
• 제40권4호
• /
• pp.139-152
• /
• 2002

This study was performed to estimate living cost for the elderly couple living in a city in Korea. Living cost means expenditure per month for elderly couple. It was assumed that the elderly couple will need different living cost according to their circumstances. The circumstances are health status, retirement status, and the level of living they want. The subjects were the elderly couple households over the age 65 of household head. Total number of subject was 1,649 households. Used data was Annual Report surveyed by National Statistical Office on the Family Income and Expenditure. Analysis of data was done through frequency, percentage, means, median using SAS Program. The results of this study were as follows: Their standard living cost was 844,980 won by pure relative standard line and 842,300 won by quasi relative standard lines. And minimum living cost was 713,400 won by the former, by the latter was 557,600 won (3/2 of median). And abundant Living cost was 1,068,020 won by the former, by the latter 1,263,450 won. The living cost of elderly households was about 81-83%, comparing with non-elderly households. Among the item of expenditure, the proportion of housing and medical care cost was larger than any other items.

• Journal of Welding and Joining
• /
• 제17권4호
• /
• pp.85-92
• /
• 1999

In GMAW, the spatter is generated because of the variation of the arc state. If the arc state is quantitatively assessed, the control method to make the spatter be reduced is able to develop. This study was attempted to develop the optimal model that could estimate the arc state quantitatively. To do this, the generated spatters was captured under the limited welding conditions, and the waveforms of the arc voltage and of the welding current were collected. From the collected waveforms, the waveform factors and their standard deviations were produced, and the linear and non-linear regression models constituted using the factors and their standard deviations are proposed to estimate the arc state. the performance test to the proposed models was practiced. Obtained results are as follow. From the results of correlation analysis between the factors and the amount of the generated spatters, the standard deviations of the waveform factors have more the multiple regression coefficients than the waveform factors. Because the correlation coefficient between T and {TEX}$T_{a}${/TEX}, and s[T] and s[{TEX}$T_{a}${/TEX}] was nearly one, it was found that these factors have the same effect to the spatter generation. In the regression models to estimate the arc state, it was fond that the linear and the non linear models were also consisted of similar factors. In addition, the linear regression model was assessed the optimal model for estimating the arc state because the variance of data was narrow and multiple regression coefficient was highest among the models. But in the welding conditions which the amount of the generated spatters were small, it was found that the non linear regression model had better the estimation performance for the spatter generation than the linear.

• 한국정밀공학회지
• /
• 제19권9호
• /
• pp.51-58
• /
• 2002

Vehicle dynamics control systems are. complex and non-linear, so they have difficulties in developing a controller for the anti-lock braking systems and the auto-traction systems. Currently the fuzzy-logic technique to estimate the absolute vehicle speed is good results in normal conditions. But the estimation error in severe braking is discontented. In this paper, we estimate the absolute vehicle speed by using the wheel speed data from standard 50-tooth anti-lock braking system wheel speed sensors. Radial symmetric basis function of the neural network model is proposed to implement and estimate the absolute vehicle speed, and principal component analysis on input data is used. Ten algorithms are verified experimentally to estimate the absolute vehicle speed and one of those is perfectly shown to estimate the vehicle speed with a 4% error during a braking maneuver.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2000년도 추계학술대회 논문집
• /
• pp.450-457
• /
• 2000

This paper establishes a scheme to estimate track quality using standard deviation and deterioration rate of track irregularities. To provide index of quality, standard deviation and deterioration rate of track irregularities are analyed. As an index, standard deviation and deterioration rate were applied to decision of corrective maintenance and replacement maintenance, respectively. Further, this paper proposes a basic scheme for a modernization of mechanize track maintenance that using MTT(Multiple Tie Tamper) and Ballast Cleaner.

• 응용통계연구
• /
• 제30권3호
• /
• pp.453-462
• /
• 2017

성향점수 매칭은 관찰연구에서 처리효과 추정 시 혼란변수에 의한 편의를 줄이기 위해 자주 사용되는 방법이다. 매칭을 위해 처리군에 대응되는 대조군 선정 시 처리군의 일부가 탈락되는 경우가 발생할 수 있는데, 이로 인해 편의가 발생할 수 있다. 최근, Austin (2017)의 연구에서 이중 성향점수 보정(double propensity score adjustment)방법을 사용하는 것이 이에 대한 해결책이 될 수 있음을 제시하였다. 하지만, 처리효과 추정치의 표준오차는 이론적 추정치가 제시되지 않아 추정에 어려움이 있다. 본 연구에서는 이중 성향점수 보정 방법을 이용한 처리효과 추정치의 표준오차 추정을 위하여 두 가지 붓스트랩 방법을 제안한다. 첫 번째는 원 자료에서 성향점수 매칭 후 매칭 된 표본에서 붓스트랩 표본을 얻는 방법(simple 붓스트랩)이고, 두 번째는 원 자료에서 붓스트랩을 먼저 시행하고 각 붓 스트랩 표본에서 성향점수 매칭을 하는 방법(complex 붓스트랩)이다. 두 방법의 성능을 비교하기 위하여 다양한 상황을 가정하여 모의실험을 시행한 결과 complex 붓스트랩 방법이 경험적 표준오차와 더 가까운 값으로 추정함을 알 수 있었다. 95% 신뢰구간의 포함확률도 complex 방법을 사용했을 때 0.95에 훨씬 가까웠다. 실제 자료에 적용하였을 때에도 simple 방법은 complex 방법에 비해 표준오차를 작게 추정하였다.

• 한국IT서비스학회지
• /
• 제8권2호
• /
• pp.43-70
• /
• 2009

As software development and maintenance cost increase quickly, information systems managers are more concerned about how to effectively manage software cost. To estimate the software development cost, most public institutes of Korea use the software cost estimation standard established by the government. Unfortunately, the accuracy of the estimation derived from the standard has not been satisfactory in spite of repetitive modifications made to improve it. One of the major reasons for the inaccuracy is that the standard has too small a number of cost adjustment factors to reflect the various characteristics of a software development project. To remedy this problem, we propose new cost adjustment factors which can be incorporated into the standard and are important to enhance the estimation accuracy, based on the analysis of several well-known software estimation models. Furthermore, by applying the proposed model to real world software projects, we show that the proposed model can produce more accurate estimates than the current standard.