Takenori Sakumura

Hosei University · Department of Industrial and Systems Engineering

The plug-in predictor of the posterior mean of the canonical parameter minimizes the posterior mean of the Kullback-Leibler loss in the exponential family. We observe that the posterior mean under the reference prior implies an approximately unbiased estimator of a suitably chosen form of the parameter. In fact, amounts of bias are very small, even...

We aim at improving the accuracy of indoor position estimation through a statistical approach. In this study, we propose a position estimation method based on Time-of-Arrival (ToA). ToA data are often useful. However, ToA data include a positive bias due to the reflection of radio waves. Therefore, it is difficult to estimate the TAG position from...

The extended cumulative exposure model (ECEM) includes features of the cumulative exposure model (CEM) and the memoryless model (MM). These often used to express the failure probability model in step-stress accelerated life test (SSALT). The CEM is widely accepted in reliability fields because accumulation of fatigue is considered to be reasonable....

The directional tests consider the sample on [0, 2π) although the angular data of line segments are on [0, π). We will derive the LM test statistic for the conditional von Mises distribution for testing non-uniformity of angles of line segments spread on the two dimensional plane, which has relatively high performance even for small samples as the...

Prediction of seasonal infectious disease spread is traditionally dealt with as a function of time. Typical methods are time series analysis such as ARIMA (autoregressive, integrated, and moving average) or ANN (artificial neural networks). However, if we regard the time series data as the matrix form, e.g., consisting of yearly magnitude in row an...

We construct mathematical models to represent the relationship between the thermal stress and the deterioration rate for electrical insulation. The Arrhenius-log-normal model has been used generally for such a deterioration model due to the thermal stress. The Arrhenius law is based on the chemical reaction theory between the absolute temperature a...

Assuming that the Arrhenius law holds between the thermal stress and the lifetime, and that the logarithmic lifetime follows some consistent probability distributions at a constant stress. Under such life models, it is crucial to show the optimum test design from an efficiency viewpoint. It would also be useful to know the semi-optimum test plan in...

The item response theory (IRT) can estimate the parameters for the items of problems and the abilities of students by using the matrix of answering pattern. The conventional IRT is applied to the complete matrix in which all the students answered to all the problems. In this paper, we have proposed the EM-type IRT method which allows the vacant ele...

Many researchers know the superiority of the item response theory (IRT) over the classical test theory (CTT) from a detailed test-evaluation viewpoint. However, teachers are still reluctant to use the IRT as a daily testing tool. The primary objective of this paper is to nd the difference between the CTT and the IRT. In particular, we focus on the...

The matrix decomposition is one of the most powerful methods in recommendation systems. In the recommendation system, we can assume an incomplete matrix consisted of observed evaluation values by users and items, then we predict the vacant elements of the matrix using the observed values. This method is applied to a variety of the fields, e.g., for...

The cumulative exposure model (CEM) is often used to express the failure probability model in step-stress accelerated life tests (SSALT). This probability model is widely accepted because accumulation of fatigue is considered to be reasonable. Contrary to this assumption, the memoryless model (MM) is also used in electrical engineering because accu...

The item response theory (IRT) gives us the valuable information about the difficulties of problems as well as the abilities of students, whereas the classical test method provides only the abilities of students with pre-determined scores to each problem. To enhance the use of the IRT, we have developed a concise IRT evaluation Web system via the d...

Although the superiority of the test method using the item response theory (IRT) over the classical test method is valid for regular examinations such as the midterm and final tests in universities and colleges, the IRT is not known to teachers in universities and colleges. To enhance the chance of use of this new methpd, we have developed a test e...