Bias-reduced ℓ_1-trend filtering

Yu Donghyeon,Lim Johan,Son Won 한국통계학회 2023 Communications for statistical applications and me Vol.30 No.2

The ℓ_1-trend filtering method is one of the most widely used methods for extracting underlying trends from noisy observations. Contrary to the Hodrick-Prescott filtering, the ℓ_1-trend filtering gives piecewise linear trends. One of the advantages of the ℓ_1-trend filtering is that it can be used for identifying change points in piecewise linear trends. However, since the ℓ_1-trend filtering employs total variation as a penalty term, estimated piecewise linear trends tend to be biased. In this study, we demonstrate the biasedness of the ℓ_1-trend filtering in trend level estimation and propose a two-stage bias-reduction procedure. The newly suggested estimator is based on the estimated change points of the ℓ_1-trend filtering. Numerical examples illustrate that the proposed method yields less biased estimates for piecewise linear trends.

Investigation of Trend Variations in Annual Maximum Rainfalls in South Korea

서린,김태웅,권현한 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.2

Hydrologic frequency analysis practically assumes that a time series of interest is temporally stationary. However, the assumption is sometimes not valid within the context of climate change. Monotonic trend tests, which are widely used in practice to investigate the presence of significant non-stationarity of hydrologic variables, can determine only whether a trend is significant. This study proposed a practical method for characterizing trend pattern embedded in hydrologic observations through the efficient illustration of changes in trend significance over time. This study analyzed the trend patterns of observed rainfalls in the Han River basin using Mann-Kendall test, and developed checker board plots to show the pattern of trend variations. The results indicate that the time and the magnitude of significant trend would differ by station although most of record periods show a certain trend of increasing annual maximum rainfalls.

Spatial and Temporal Trends in High Resolution Gridded Temperature Data over India

Grace Nengzouzam,Sanayanbi Hodam,Arnab Bandyopadhyay,Aditi Bhadra 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.4

The changing temperature, directly and indirectly, has significant effect on the agricultural production and economy of the country which necessitates detailed study of the spatial and temporal variability of temperature. This paper focuses on the spatio-temporal trend analysis of minimum and maximum temperature over India. Daily gridded temperature data with spatial resolution of 1° × 1° for the period of 1969–2005 were analysed using Mann-Kendall (MK) non-parametric test at 3 levels of significances, namely, 1%, 5%, and 10%. The diurnal temperature range was also analysed. Results showed that maximum temperature experienced significant decreasing trends in the entire Indo-Gangetic plains extending up to the NE region while the Southern region experienced warming. For minimum temperature, all regions except the Central region reported increasing trends indicating warming. As a result, diurnal temperature range showed decreasing trends in many places in the upper half of the country while the lower half is dominated by increasing trends. On a regional scale, the Southern region, in particular, showed increasing trends in all three parameters. On seasonal scale, pre-monsoon and monsoon months remained mostly trendless for all three parameters. Maximum significant decreasing trends were observed during January–May while maximum increasing trends were reported during June–December. Also, a higher Sen slope value of the yearly maximum increase in the minimum temperature indicated steeper increase in minimum temperature over maximum temperature.

조정된 변이계수 접근법을 활용한 가격안정화 효과 추정: 수산업관측사업을 중심으로

김용준 ( Yong Joon Kim ),안동환 ( Dong Hwan An ),김관수 ( Kwan Soo Kim ) 한국축산경영학회 2015 농업경영정책연구 Vol.42 No.1

The purpose of this paper is to measure price stabilization effects of fisheries outlook project implemented by the government since 2004. Given the problems associated with the use of a simple coefficient of variation approach, we applied a refined version of coefficient of variation: 1) trend equation is incorporated; 2) a structural change is explicitly taken into consideration. While we found significant price stabilization effects of outlook information on Laver (a kind of seaweed), we found no significant price stabilization effects in the case of Oyster as the presence of stabilization effects tend to be sensitive to the type of coefficient of variation used in the analysis. This suggests a need for careful consideration of pros and cons associated with the use of coefficient of variation in an empirical analysis.

Spatial and Temporal Variation of Annual and Categorized Precipitation in the Han River Basin, South Korea

Sabab Ali Shah,Muhammad Jehanzaib,김민지,곽동엽,김태웅 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.4

The effects of variations in annual, seasonal, and extreme precipitation in the Han River Basin (HRB) were explored using innovative trend analysis, Spearmen’s rho test, and Mann-Kendall test. Extreme-value precipitation was analyzed using various precipitation categories (light, low, moderate, high, and extreme). Stations in the north and northeast parts of the basin were more sensitive to precipitation inconsistencies. Hydrologically extreme events such as flood and drought were associated with extreme (> 90th percentile) and light (< 10th percentile) precipitation categories. Significant variability was detected in summer precipitation, whereas annual and extreme precipitation trends were more sensitive in the northeastern parts of the basin, signifying possible flooding aggregation. However, a decrease in flooding in the southern HRB indicated a shift in the precipitation regime from south to north. Overall results suggest that the eastern and northwestern regions were more likely to experience extreme floods during the summer and severe droughts during the fall and winter. An increase in precipitation was observed over time from the south to the north. A warming and wetting trend was observed in the north, while a warming-drying trend was evident in the south. Mitigating hydro-meteorological disasters such as flood and drought in the HRB will require more research attention to these trends.

Time series analysis of patients seeking orthodontic treatment at Seoul National University Dental Hospital over the past decade

Hyun-Woo Lim,Ji-Hoon Park,Hyun-Hee Park,Shin-Jae Lee 대한치과교정학회 2017 대한치과교정학회지 Vol.47 No.5

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 singlecenter 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.

거부민감성 관련 국내 연구동향 분석

박은경(Park Eun kyung),선혜연(Seon Hye yon) 학습자중심교과교육학회 2018 학습자중심교과교육연구 Vol.18 No.14

본 연구의 목적은 거부민감성에 대한 연구 동향을 파악하고 이 연구가 나아가야 할 방향을 제시하는 것이다. 이를 위해 2000년부터 2018년 5월까지 국내 등재학술지에 게재된 거부민감성 연구 총 67편을 연구대상, 연구방법, 연구주제 및 관련변인, 측정도구를 분석하였다. 연구결과는 다음과 같다. 첫째, 거부민감성에 대한 연구들은 2013년 이후로 꾸준하게 연구가 이루어진 것으로 나타났다. 둘째, 연구대상은 대학(원)생을 대상으로 한 연구가 가장 많았고, 초등학생, 중학생, 고등학생 순으로 나타났으며, 성별의 차이를 본 연구가 성별의 차이를 보지 않은 연구보다 상대적으로 적었다. 셋째, 연구방법 면에서는 문헌연구 1편을 제외하고는 모두 양적연구였으며, 질적자료를 분석한 연구는 찾아보기 어려웠다. 넷째, 거부민감성에 영향을 주는 변인으 로는 부모 변인이 가장 많았고, 내적 변인, 또래 및 학교변인 순으로 나타났다. 다섯째, 거부민감성의 종속변인은 정서 및 성격 요인이 가장 많았고, 행동요인, 관계 및 적응 요인, 인지 요인 순으로 나타났다. 여섯째, 거부민감성 측정도구는 연구대상에 따라 제한적으로 사용되고 있었다. 이러한 연구결과를 바탕으로 거부민감성에 대한 추후 연구의 나아갈 방향과 부가적으로 요구되는 연구주제들에 대하여 논의하였다. The purpose of this study is to identify trends in research on rejection sensitivity and provide directions for this study. To that end, a total of 67 rejection sensitivity studies published in the KCI registration Journals in Korea from 2000 to May 2018 were analyzed for subjects, methods of research, topics of study, and related variations, measurement tools. The results of the study are as follows. First, studies of rejection sensitivity have been shown to have been consistently studied since 2013. Second, the subjects were the most university students, followed by elementary, middle and high school students, and the study on gender differences was not less different than the study on gender. Third, in terms of research methods, all were quantitative except for the first volume of literature, and no qualitative researcher was found. Fourth,, parents were the most likely to influence rejection sensitivity, followed by internal variation, peer and school variation. Fifth, the dependent variant of rejection sensitivity had the most number of emotional and personality factors, followed by behavior, relationship and adaptation, and cognitive factors. Sixth, reject sensitivity measurement tools were used on a limited basis depending on the subject of the study. Based on these findings, further studies on rejection sensitivity were discussed and additional required research subjects were discussed.

진해 용원수로의 COD 및 영양염류 농도 추세분석

조홍연(Cho, Hong-Yeon),채장원(Chae, Jang-Won),박정규(Park, Joung-Guy),구명서(Koo, Myung-Seo) 한국해안해양공학회 2008 한국해안해양공학회 논문집 Vol.20 No.4

부산 신항 개발사업으로 형성된 용원수로는 좁고 긴 형태로 해수흐름이 정체되어 환경악화가 우려되는 지역이다. 본 연구에서는 2003년부터 2007년까지의 월별 관측 자료를 이용하여 용원수로의 수질변화 양상을 분석하였다. 추정된 연평균 농도와 오차범위를 분석한 결과 용원수로 내부가 용원수로 입구에 비하여 전반적으로 뚜렷하게 수질이 악화되어 있는 것으로 파악되었다. 수로 입구의 수질농도를 기준으로 수로 내부의 수질농도는 COD, TN, TP 항목의 경우 각각 1.34배, 2.08배, 1.80배로 높은 것으로 파악되었다. 한편, Mann-Kendall 방법을 이용한 오염물질 농도변화의 추세검정 결과, 일반적으로 사용되는 95% 신뢰수준에서 추세를 가지는 경우는 SW-26 지점 TP 항목(증가추세)을 제외하고는 모두 뚜렷한 변화 추세는 없는(엄밀한 통계적인 용어로는 "있지 않은") 것으로 파악되었다. Youngwon channel located in Chinhae city and formed by the Busan New Port Construction Project has been concerned about the water quality degradation problems because of the flow and pollutants stagnation due to its long-narrow shape. In this study, the water quality(hereafter WQ) variation is analysed by using the monthly WQ data measured in Yongwon channel from 2003 to 2007. The analysis shows that the TN and TP concentration in the inside Yongwon channel is definitely worse than the TN and TP concentration in the entrance of the Yongwon channel based on the 95% confidence level. The COD, TN, and TP concentrations in the Yongwon channel are 1.34, 2.08, and 1.80 times larger than that in the entrance of the Yongwon channel, respectively. It has been found that only the TP concentration in SW-26 station has an increasing trend based on the Mann-Kendall test with respect to 95% confidence level. The other stations and the other WQ constituent changes do not have the any significant trends.

우리나라 강수량과 일평균기온의 시·공간적 특성변화 분석

이원현,홍성현,김영규,정은성 한국방재학회 2011 한국방재학회논문집 Vol.11 No.4

This study analyzed the recent changed temporal and spatial variations of precipitation and daily average temperature in the South Korea. 65 weather stations were grouped, based on their latitudes and longitudes and the recent variable temporal and spatial variations of each latitude and longitude were derived, quantitatively. In addition, the Mann-Kendall trend analysis was used to determine the tendency (upward/downward/no trend) of rainfall and temperature. From these analyses, it was shown that the precipitation of zone 1 (33°-34°) has increased by 7% and the rate of increase showed 5%∼18% as the latitude went up. During summer, the rate of precipitation increase has increased as the latitude went up. Due to the rapid increase of summer, the rate of precipitation increase has increased as the longitude went up. On the whole, average temperature has been increased as the latitude went up. The Mann-Kendall trend analysis derived that the temperature of South Korea has increased except zone 2 (34°-35°)and summer period and the precipitation on latitude 36°∼38° and longitude 126°∼130° has increased during summer. Since this study showed the recent climate change trend in detail, it will be a preliminary data for the research of climate change adaptation. 본 연구는 1991년 이전부터 관측을 시작한 65개 기상청 관측소의 강수량과 평균기온 자료를 이용하여 2000년 이전으로 대표되는 과거 자료와 2001년 이후로 대표되는 최근 자료를 계절별로 분석하여 시·공간적 특성을 분석하였다. 관측소를 위도, 경도별로 각각 분류하여 강수량과 일평균기온의 특성을 2000년 이전과 이후에 대해 비교하였다. 또한 증감 여부를 확인하기 위해 가장 많이 사용되는 Mann-Kendall 경향성 분석 기법을 적용하였다. 위도별 분석 결과 일평균강수량의 경우 33°∼34°(제주도)에서는 7%이상의 증가율을 보였고 남부지방에서 북부지방으로 위도가 올라갈수록 증가율이 5%∼18%까지 증가하였다. 여름의 경우 계절별로 살펴보면, 위도가 증가함에 따라 강수량의 증가율도 증가하였다. 경도별 분석 결과 130°∼131°(울릉도)에서 평균적으로 30%이상의 증가율을 보였고 서에서 동쪽으로 갈수록 증가율의 추이가 여름철의 증가 경향으로 인해 증가한다는 것을 알 수 있다. 평균 기온은 위도가 39°∼40° 가을철과 겨울철의 기온차가 최대 1.0℃ 이상 증가하는 추이를 보이고 있으며 경도가 129°∼130°에서 특징적으로 기온이 상승했다. 또한 경향성 분석결과 일평균기온의 경우 일부 지역(34°∼35°)과 여름철을 제외하면 전국적으로 봄, 가을, 겨울에 증가하는 경향이 나타났으며, 강수량의 경우 여름철에 36°∼38°, 126°∼130° 지역에 집중적으로 증가하는 경향을 보였다. 본 연구의 결과는 최근 우리나라 기후변화 경향을 구체적으로 제시하고 있으므로 기후변화 대비 적응 연구의 기초자료로 활용될 수 있다.

Spatio-Temporal Variations of Optical Properties of Aerosols in East Asia Measured by MODIS and Relation to the Ground-Based Mass Concentrations Observed in Central Korea during 2001~2010

김학성,Yong-Seung Chung,Joon-Tae Kim 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.2

Long-term variations and trends of atmospheric aerosolsin the East Asian region were analyzed by using aerosol optical depth(AOD or τ), and ångström exponent (AE or α) obtained from theModerate Resolution Imaging Spectroradiometer (MODIS) from 2001to 2010. The increased emission of anthropogenic fine aerosols ineast China resulted in the high AOD in this region during summer. The steady increasing emission of anthropogenic fine aerosols causedan increasing trend of AOD in east China, and the large-scaletransport of sandstorms and smoke plume caused by forest firesaffected intense inter-annual variations of AOD in the East Asianregion. While in the central part of South Korea, located in the leeside of the East Asian continent, AE tended to rise to a level higherthan in east China, the ground-based mass concentrations continuedto decline. A noticeable decrease of PM10 mass concentration inspring and winter in central Korea is most likely attributable todecreases in sandstorms in the source region of East Asia. However,the ratio of PM2.5 mass concentration to PM10 increases overallwith a high level in summer. Aerosol types were classified into dust,smoke plume, and sulphate by using satellite data over Cheongwon incentral Korea. The columnar AOD, with different aerosol types, wascompared with the ground-based mass concentrations at Cheongwon,and the relatively high level of the correlations presented betweenPM2.5 and AOD produced in sulphate. Growth and increases of finehygroscopic aerosols generated as gas-to-particle conversion particularlyin summer contribute to increases of columnar AOD in the EastAsian region.