• The Korean Journal of Applied Statistics
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• v.22 no.6
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• pp.1315-1329
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• 2009

The panel survey is need to have a more concern about a response due to a secession and non-response of a sample. And generally a population is not fixed and continuously changed. Thus, the rotation sample design can be used by the method replacing the panel research. This paper is the study of comparison to equal weight method, Duncan weight, Design weight method, weight share method in rotation sample design. More specifically, this paper compared variance estimators about the existing each method for the efficiency comparison, and to compare the precision using the relative efficiency gain by the Coefficient Variance(CV) after getting the design weight from the actual data.

• The Korean Journal of Nuclear Medicine
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• v.32 no.5
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• pp.414-424
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• 1998

Purpose: Cross-modality coregistration of positron emission tomography (PET) and magnetic resonance imaging (MR) could enhance the clinical information. In this study we propose a refined technique to improve the robustness of registration, and to implement more realistic visualization of the coregistered images. Materials and Methods: Using the sinogram of PET emission scan, we extracted the robust head boundary and used boundary-enhanced PET to coregister PET with MR. The pixels having 10% of maximum pixel value were considered as the boundary of sinogram. Boundary pixel values were exchanged with maximum value of sinogram. One hundred eighty boundary points were extracted at intervals of about 2 degree using simple threshold method from each slice of MR images. Best affined transformation between the two point sets was performed using least square fitting which should minimize the sum of Euclidean distance between the point sets. We reduced calculation time using pre-defined distance map. Finally we developed an automatic coregistration program using this boundary detection and surface matching technique. We designed a new weighted normalization technique to display the coregistered PET and MR images simultaneously. Results: Using our newly developed method, robust extraction of head boundary was possible and spatial registration was successfully performed. Mean displacement error was less than 2.0 mm. In visualization of coregistered images using weighted normalization method, structures shown in MR image could be realistically represented. Conclusion: Our refined technique could practically enhance the performance of automated three dimensional coregistration.

• The Korean Journal of Applied Statistics
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• v.31 no.2
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• pp.229-239
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• 2018

This paper introduces how to adopt the concept of temporal hierarchies to forecast time series data. Similarly as in hierarchical cross-sectional data, temporal hierarchies can be constructed for any time series data by means of non-overlapping temporal aggregation. Reconciliation forecasts with temporal hierarchies result in more accurate and robust forecasts when compared with the independent base and bottom-up forecasts. As an empirical example, we forecast traffic accident counts with temporal hierarchies and observe that reconciliation forecasts are superior to the base and bottom-up forecasts in terms of forecast accuracy.

• The Korean Journal of Financial Management
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• v.24 no.1
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• pp.29-58
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• 2007

We develop a model to estimate the value of growth opportunities, which is based on the seminal papers of M&M(1961, 1963) and Lee(2006). Making use of the estimation model, we estimate a new proxy variable of the growth opportunities, other than the usual proxy variables such as quasi Tobin's Q, MBR, and so on. The new proxy variable of growth opportunities can represent a necessary condition to identify whether the increase in new investments are successful or not. The empirical findings on the growth opportunities during the IMF currency crisis period and the post-IMF period are as follows; First, the overall success rate of new investments is as low as 50%, that means only half of the listed firms were increasing new investments when they had the growth opportunities. Second, during the crisis, one third of the listed firms were experiencing negative growth opportunities. However, during the post-IMF period, the growth opportunities on new investments were turned to be positive due to the turnaround efforts of listed firms. Third, the value of intangible assets, which are resulting from the investment of R&D and human capital, are becoming more important than ever. It seems to be true that larger portions of the value of growth opportunities are coming from the intangible assets, not from the increases in new investments of the physical assets.