• Communications for Statistical Applications and Methods
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• 제26권1호
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• pp.27-34
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• 2019

We study the effect of detrending on the coherency between two time series processes. Many economic and financial time series variables include nonstationary components; however, we analyze the two most popular cases of stochastic and deterministic trends. We analyze the asymptotic behavior of coherency under incorrect detrending, which includes the cases of first-differencing the deterministic trend process and, conversely, the time trend removal of the unit root process. A simulation study is performed to investigate the finite sample performance of the sample coherency due to incorrect detrending. Our work is expected to draw attention to the possible distortion of coherency when the series are incorrectly detrended. Further, our results can extend to various specification of trends in aggregate time series variables.

• Asian Pacific Journal of Cancer Prevention
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• 제15권7호
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• pp.3105-3112
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• 2014

Purpose: To examine breast cancer (BC) incidence trends in relation to mammographic screening and risk factor prevalence in South Australia (SA). Materials and Methods: Trends in annual BC incidence rates were calculated using direct standardisation and compared with projected incidence derived from Poisson regression analysis of pre-screening rates. Annual percentage change and change time points were estimated using Joinpoint software. Biennial mammography screening participation rates were calculated using data from BreastScreen SA. Trends in overweight/obesity, alcohol use and hormone replacement therapy (HRT) use were examined using 1991-2009 Health Omnibus Survey data. Trends in total fertility were examined using data from the Australian Bureau of Statistics. Results: BC incidence increased around the time BreastScreen commenced and then stabilised in the mid-1990s. However rates have remained higher than projected, even though the proportion and age distribution of first time screening attendees stabilised around 1998. A decrease in BC incidence was observed among women aged 50-59yrs from the late-1990's but not among older women. Obesity and alcohol use have increased steadily in all age groups, while HRT use declined sharply from the late-1990s. Conclusions: BC incidence has remained higher than projected since mammography screening began. The sustained elevation is likely to be due to lead time effects, though over-diagnosis cannot be excluded. Declining HRT use has also impacted incidence trends. Implications: Studies using individual level data, which can account for changes in risk factor prevalence and lead time effects, are required to evaluate 'over-diagnosis' due to screening.

• 복식문화연구
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• 제18권6호
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• pp.1274-1290
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• 2010

This study analyzed the design elements and fashion images of women's knitwear in collections of Paris, Milan, London and New York between 2003 and 2008, and examined knitwear trends in an effort to verify whether knitwear trends are repeated in certain cycles, whether they show complicated patterns in cycles and yet occur in quasi cycles, or whether they occur non-periodically in complicated forms of chaotic cycles. Trend cycle analysis results are deemed to identify the time series attribute of knit fashions. It also sought to categorize the attribute of various factors influencing knitwear trends with a view to determining relevancy between design elements, and to present the direction of predicting knitwear fashion trends and the progression of short-term knitwear trends. This study reached the following conclusion. According to design elements or fashion images, knitwear fashion trends occur in cycles, quasi cycles, non-periodical cycles. These cyclic characteristics can be used as scientific data for planning knitwear products. The study confirmed close relevancy between fashion images and fashion elements. It identified close relevancy between designs with similar fashion elements and images through coordinates by year and season, and it is possible to make short-term prediction of trend direction through the flow of coordinates. Time series data were insufficient, thereby making it difficult to perfectly verify chaos indices and giving limitations to this study. A study with more time series data will produce a more effective method of predicting and using knitwear fashion trends.

• Asian Pacific Journal of Cancer Prevention
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• 제16권8호
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• pp.3097-3100
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• 2015

Projections of cancer cases are particularly useful in developing countries to plan and prioritize both diagnostic and treatment facilities. In the prediction of cancer cases for the future period say after 5 years or after 10 years, it is imperative to use the knowledge of past time trends in incidence rates as well as in population at risk. In most of the recently published studies the duration for which the time trend was assessed was more than 10 years while in few studies the duration was between 5-7 years. This raises the question as to what is the optimum time period which should be used for assessment of time trends and projections. Thus, the present paper explores the suitability of different time periods to predict the future rates so that the valid projections of cancer burden can be done for India. The cancer incidence data of selected cancer sites of Bangalore, Bhopal, Chennai, Delhi and Mumbai PBCR for the period of 1991-2009 was utilized. The three time periods were selected namely 1991-2005; 1996-2005, 1999-2005 to assess the time trends and projections. For the five selected sites, each for males and females and for each registry, the time trend was assessed and the linear regression equation was obtained to give prediction for the years 2006, 2007, 2008 and 2009. These predictions were compared with actual incidence data. The time period giving the least error in prediction was adjudged as the best. The result of the current analysis suggested that for projections of cancer cases, the 10 years duration data are most appropriate as compared to 7 year or 15 year incidence data.

• Journal of Preventive Medicine and Public Health
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• 제46권3호
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• pp.139-146
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• 2013

Objectives: Cigarette smoking prevalence among adolescent males in rural areas of Korea has increased in recent years. The aim of this study was to explore the factors related to increasing trends in cigarette smoking among adolescent males living in rural areas. Methods: The raw data from the Korea Youth Risk Behavior Web-based Survey from 2006 to 2009 were used. Data were analyzed by using the method of complex survey data analysis considering complex sampling design. Multiple logistic regression models were used to explore the factors affecting cigarette smoking. We evaluated the linear time trends in the prevalence of factors that were related to current smoking status and the linear time trends in cigarette smoking in groups stratified by the exposure to each factor using logistic regression models. Finally, we examined the contributions of the factors to the time trends in cigarette smoking by adjusting for each of those factors in the baseline regression models and changes in the adjusted odds ratio by survey year. Results: A statistically significant increasing trend in smoking was observed after adjusting for the factors affecting cigarette smoking. Significant factors related to cigarette use were perceived stress, experience with depression, current alcohol drinking, exposure to secondhand smoke, and academic performance. The factor related to increasing trends in cigarette smoking was academic performance. Conclusions: Stress about academic performance is an important factor affecting the increase in cigarette smoking among adolescent males in a rural area of Korea.

• 한국패션뷰티학회지
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• 제2권1호
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• pp.34-45
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• 2004

Hair styles which independently coexist by transcending the time and space under the environment of highly developed information and communication technology of recent years, were analyzed. Moreover the concerned trends of art which influenced on these styles were introduced in this study. Through IT based information exchange produced new hair styles which have the technological images. The characteristics of these hair styles are investigated also. For the examination of yearly trends, hair styles in fashion collections of Yves Saint Larent during 1962 to 1999 were examined and classified. The results show that time variated trends are appeared in this period. For the analysis of the trends of hair styles featuring technological images, hair styles in fashion collection of Christian Dior, Giorgio Armani, Gucci, Jean Paul Gaultier and Chanel in the early 2000s are quoted.

• 대한치과교정학회지
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• 제47권5호
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• pp.298-305
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• 2017

Objective: This paper describes changes in the characteristics of patients seeking orthodontic treatment over the past decade and the treatment they received, to identify any seasonal variations or trends. Methods: This single-center retrospective cohort study included all patients who presented to Seoul National University Dental Hospital for orthodontic diagnosis and treatment between January 1, 2005 and December 31, 2015. The study analyzed a set of heterogeneous variables grouped into the following categories: demographic (age, gender, and address), clinical (Angle Classification, anomaly, mode of orthodontic treatment, removable appliances for Phase 1 treatment, fixed appliances for Phase 2 treatment, orthognathic surgery, extraction, mini-plate, mini-implant, and patient transfer) and time-related variables (date of first visit and orthodontic treatment time). Time series analysis was applied to each variable. Results: The sample included 14,510 patients with a median age of 19.5 years. The number of patients and their ages demonstrated a clear seasonal variation, which peaked in the summer and winter. Increasing trends were observed for the proportion of male patients, use of non-extraction treatment modality, use of ceramic brackets, patients from provinces outside the Seoul region at large, patients transferred from private practitioners, and patients who underwent orthognathic surgery performed by university surgeons. Decreasing trends included the use of metal brackets and orthodontic treatment time. Conclusions: Time series analysis revealed a seasonal variation in some characteristics, and several variables showed changing trends over the past decade.

• 정보관리학회지
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• 제27권4호
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• pp.7-32
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• 2010

본 연구는 우리나라 대표적인 정보학분야 학회지인 "정보관리학회지"에 25년 동안에 발표된 학술논문을 대상으로 동향분석을 시도하여 각 시기별 우리나라 정보학분야의 학문적 구조와 그 변화를 파악하였다. 이를 위하여 먼저 25년을 1984-1994, 1995-2002, 2003-2009로 나눈 다음, 각 기간별 "정보관리학회지"에 실린 학술논문의 주제를 분석한 후 각 논문의 주제분포, 주제영역별 논문의 증감, 주제영역별 연도 분포를 살펴보았다. 또한 논문의 표제어를 이용하여 기간별 정보학의 지적 구조를 생성하였고 세 개의 지적 구조를 비교하여 정보학 연구의 변화를 분석하였다. 그 결과 "정보관리학회지" 연구의 주요 대주제 영역은 '정보서비스', '정보조직' 그리고 '정보시스템'이며 소주제 영역은 도서관서비스, 이용자연구, 자동문헌처리, 도서관통합시스템, 시소러스/온톨로지, 디지털도서관인 것으로 나타났다. 또한 표제어의 지적 구조를 분석한 결과, 정보학의 핵심영역은 여전히 정보검색이지만 각종 도서관이나 시스템에 활용된 정보기술 기법이나 서비스 평가에 대한 연구가 점점 늘어나고 이에 대한 주제영역이 확장되고 있음을 알 수 있었다.

• 한국환경보건학회지
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• 제23권2호
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• pp.44-56
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• 1997

When sewage sludge is treated by cornposting, higher moisture content and lower C/N ratio on sewage sludge is problems. This paper project to alesolve two problems. The almost trends in run 3 of MC 70% are similar to these in run 1 and 4 of MC 65%. A retention time of the highest temperature (>50$\circ$C) and increase rate of temperature in run 3 are an affinity to these in run 4. Particularly, decrease rate of temperature in run 3 is slower than others and this data shows the more activity of thermal microbial in run 3 than that in others. C/N ratio trends in run 3 shows slow reaction in initial stage but, after 9 days, is similar to that in run 1 and 4. Carbon trends in each run are a similarity to C/N ratio trends. Temperature, MC, carbon and C/N ratio trends in run 5, whose C/N ratio is 15, show less microbial activity than that in run 6, whose C/N ratio is 20. But temperature increase of the beginning stage and pH of the final stage in run 5 are greater than that in run 6. Final MC and carbon content in run 5 and 6 have a similar values. That is, final MC in run 5 and 6 is 49.39% and 48.97% and final carbon content in each run is 25.15% and 22.20%. Expecially, a temperature increase and C/N ratio decrease rate of the beginning stage in run 5 are greater than these in run 6. This shows the shorter lag time in run 5 than lag time in run 6.

• Fisheries and Aquatic Sciences
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• 제2권2호
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• pp.210-217
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• 1999

Chemical oxygen demand (COD), phytoplankton cell number and chlorophyll-a concentration (Chl-a), sediment mean grain size and ignition loss were studied to determine their temporal trends in the study area. Historical data of COD, cell number and Chl-a were gathered from the late 1960s or early 1980s to 1997, and trends in temporal domain were obtained from a simple regression. Sediments for grain size and ignition loss (as organic contents in sediments) were sampled from the Chokchon macrotidal flat bimonthly from September 1990 to November 1996, and were analyzed using the decomposition method of time series analysis. In general, the first three data showed increasing trends based on regression analysis. The trends of sediment grain size fluctuated in a neutral pathway while those of ignition loss yielded no increasing pattern. In contrast with the suggestions from Ahn and Choi (1998) who reported a coarsening variation in sediment grain size to be a cause of the directional and remarkable changes of macrofaunal communities in this area, we could not find such a corresponding variation pattern from our samples. In diagnosing eutrophication, a paradoxical phenomenon was encountered between the trends in water column (COD, cell number and Chl-a) and sediment (ignition loss) data. In this paper, we inferred the possible processes that produce the discrepancy. Some explanations and biological responses to eutrophication were predicted and discussed.