• The Korean Journal of Applied Statistics
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• v.32 no.5
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• pp.753-761
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• 2019

A test procedure based on a Kendall's τ statistic is proposed for the association of bivariate interval censored data. In particular, a leverage bootstrap technique is applied to replace unknown failure times and a classical adjustment method is applied for treating tied observations. The suggested method shows desirable results in simulation studies. An AIDS dataset is analyzed with the suggested method.

• Current Research on Agriculture and Life Sciences
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• v.32 no.3
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• pp.135-143
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• 2014

The variability and temporal trends of the annual and seasonal minimum and maximum temperature, rainfall, relative humidity, wind speed, sunshine hours, and runoff were analyzed for 5 major rivers in Korea from 1960 to 2010. A simple regression and non-parametric methods (Mann-Kendall test and Sen's estimator) were used in this study. The analysis results show that the minimum temperature ($T_{min}$) had a higher increasing trend than the maximum temperature ($T_{max}$), and the average temperature increased by about $0.03^{\circ}C\;yr.^{-1}$. The relative humidity and wind speed decreased by $0.02%\;yr^{-1}$ and $0.01m\;s^{-1}yr^{-1}$, respectively. With the exception of the Han River basin, the regression analysis and Mann-Kendall and Sen results failed to detect trends for the runoff and rainfall over the study period. Rapid land use changes were linked to the increase in the runoff in the Han River basin. The sensitivity of the evapotranspiration and ultimately the runoff to the meteorological variables was in the order of relative humidity > sunshine duration > wind speed > $T_{max}$ > $T_{min}$. Future studies should investigate the interaction of the variables analyzed herein, and their relative contributions to the runoff trends.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.193-193
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• 2017

Trend analysis can enhance our knowledge of the dominant processes in the area and contribute to the analysis of future climate projections. The results of previous studies in South Korea showed that southeast regions of Korea had the highest value of evapotranspiration. Thereby, it is of interest to determine the trend analysis in hydrological variables in this area. In this study, the recent 35 year trends of precipitation, reference evapotranspiration, and aridity index in monthly and annual time scale will be analyzed over three stations (Pohang, Daegu, and Pusan) of southeast Korea. After removing the significant Lag-1 serial correlation effect by pre-whitening, non-parametric statistical Mann-Kendall test was used to detect the trends. Also, the slope of trend of the Mann-Kendall test was determined by using Theil-Sen's estimator. The results of the trend analysis of reference evapotranspiration on the annual scale showed the increasing trend for the three mentioned stations, with significant increasing trend for Pusan station. The results obtained from this research can guide development if water management practices and cropping systems in the area that rely on this weather stations. The approaches use and the models fitted in this study can serve as a demonstration of how a time series trend can be analyzed.

• Journal of Environmental Impact Assessment
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• v.28 no.2
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• pp.83-100
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• 2019

This study, we conducted a non-parametric trend test (Seasonal Kendall tests, LOWESS) and Cross Correlation. We aimed to identify water quality trends using the weekly data for 9 variables (Water Temperature, EC, DO, BOD, COD, T-N, T-P, TOC and Chl-a) collected from 4 sites in the Paldang Lake from 2004.01 to 2016.12. According to the Seasonal Kendall test, Water temperature increased but EC, T-N and T-P decreased trend. LOWESS showed that BOD was gradually decreased from 2013 to 2016. but COD gradually increased between 2012 and 2016. As a result, it was confirmed that the period between 2012 and 2013 was a turning point in the increase of COD along with the decrease of BOD at all sites in Paldang Lake. Results of Cross Correlation showed that there was no time difference between all of Water variables and Sites. In this study, it is necessary to analyze the cause of the transition period and to monitoring the water quality more precisely for better water quality management in Paldang Lake.

• Journal of Soil and Groundwater Environment
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• v.14 no.5
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• pp.41-50
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• 2009

Water levels in groundwater monitoring wells of Jeju Island were analyzed using parametric and non-parametric trend analyses. Number of used monitoring wells in the analysis are 94 among totally 106 monitoring wells and the monitoring period is greater than single year, from 2001 to 2009. For the trend analysis, both parametric (linear regression) and nonparametric (Mann-Kendall trend test and Sen's trend test) methods were adopted. Results of the linear regression analysis on daily basis indicated that about 58.5% of the monitoring wells showed a decreasing trend, and analysis using monthly median indicated that about 79.8% showed a decreasing trend. The Mann-Kendall trend test and Sen's trend test with monthly median values in confidence levels of 95% and 99% showed the same analysis results. In confidence level of 95%, 32% were decreased, 3% were increased and the remains showed no trend. However, in confidence level of 99%, 16% were decreased, 2% were increased and the remains showed no trend. The largest decline rates of water levels were detected mainly at the coast of the northwestern and southwestern parts, which is expected to closely related to the increased pumping in the urban area and tourist resort.

• Journal of Navigation and Port Research
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• v.31 no.7
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• pp.623-628
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• 2007

By employing primarily the Kendall's Concordance Test, the paper attempted to conduct an experts' evaluation on the interaction among the agents in Busan marine tourism cluster and recommend some measures for policy consideration for the cluster's activation. For this purpose, a conceptual framework was developed to guide the assessment by using inter-agent cooperation and network approaches regarding the nature of the marine tourism cluster. Such factors as cooperation, competition, relationship marketing, and networking were identified as critical. Findings of the study imply that Busan marine tourism cluster is at its embryonic stage and needs desperate measures for improvement in the inter-organizational cooperation and networking, the major regional characteristics that determine the competitiveness of marine tourism.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.421-428
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• 2008

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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.295-303
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• 2010

The variability of vegetation is strongly related to the variability of hydrometeorological factors such as precipitation, temperature, runoff and so on. Analysis of the variability of vegetation will aid to understand the regional impact of climate change. Thus we analyzed the spatial-temporal variability of NOAA(National Oceanic and Atmospheric Administration)/AVHRR(Advanced Very High Resolution Radiometer) NDVI(Normalized Difference Vegetation Index). In the results from Mann-Kendall test, there is no significant linear trend of annual NDVI from 1982 to 2006 in the most area except the downward trend on the significance level 90% in the Guem-river basin area. In addition, using EOF(Empirical Orthogonal Function) analysis, the variability of NDVI in the region of higher latitude and altitude is higher than that in the other region since the spatial variability of NDVI follows the latitudinal gradient. Also we could get higher NDVI in June, July, August and September. We had the highest NDVI in Han-river basin area and the lowest in Je-Ju island.

• Journal of Acupuncture Research
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• v.31 no.2
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• pp.99-109
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• 2014

Objectives : The purpose of this study was to analysis the relationship between hours of smartphone use and neck pain in university students. Methods : A survey of 2,353 university students was conducted in Gyeonggi province and Incheon city using a self report questionnaire from April 1 to 11 2013. The questionnaire of questions regarding the hours of using smartphone, mainly used function in participant's smartphone and neck discomfort degree. Neck disability index(NDI) was used to evaluate degree of pain. The collected data were analyzed with the t-test and Kendall's tau test using the SPSS 21.0 program and R 3.1.0, respectively. Results : 1. Almost all of the survey participants(99.07 %) were smartphone users. 66.97 % of them answered that they use their smartphone daily more than 2 hours and 48.18 % of them answered that they use their smartphone 10 to 30 minutes everytime they use it. 2. The overall distribution of NDI scores was 'no disability(0~4 score, 62.92 %)', 'mild disability(5~14 score, 32.85 %)', 'moderate disability(15~24 score, 1.19 %)'. As a result of t-test, we found that the average NDI score for female students was significantly higher than the average NDI score for male students(p<0.05). 3. The Kendall's tau test revealed that total time spent daily using smartphones has a strong positive correlation with 'pain intensity', 'lifting', 'reading' 'headache', 'concentration', and 'driving'(p<0.05) in NDI. Also, time duration of one time smartphone usage has a strong positive correlation with 'pain intensity', 'lifting', 'reading', 'headache', 'concentration', 'work', and 'recreation'(p<0.05). 4. The Kendall's tau test revealed that total NDI scores have a significantly strong positive correlation with both of total time spent daily using smartphones(p<0.05) and time duration for one time smartphone usage(p<0.05). This results imply that long-time use of smartphone has a strong relationship with neck pain. Conclusions : The results of the study would be a good starting point for future studies to reduce the risks of chronic neck pain caused by smartphone usage.

• Journal of Environmental Science International
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• v.27 no.11
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• pp.1029-1048
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• 2018

In this study, seasonal Mann - Kendall test method was applied to 12 stations of the water quality measurement network of Nam-River based on data of BOD, COD, TN and TP for 11 years from January 2005 to December 2015 The changes of water quality at each station were examined through linear trends and the tendency of water quality change during the study period was analyzed by applying the locally weighted scatter plot smoother (LOWESS) method. In addition, spatial trends of the whole Nam-River were examined by items. The flow-adjusted seasonal Kendall test was performed to remove the flow at the water quality measurement station. As a result, BOD, COD concentration showed "no trand" and TN and TP concentration showed "down trand" in regional Kendall test throughout the study period. BOD and TP concentration in "no trand", COD, and TN concentration showed an "up trand" tendency in Nam-River dam. LOWESS analysis showed no significant water quality change in most of the analysis items and stations, but water quality fluctuation characteristics were shown at some stations such as NR1 (Kyungho-River 1), NR2 (Kyungho-River 2), NR3 (Nam-River), NR6 (Nam-River 2A). In addition, the flow-adjusted seasonal Kendall results showed that the BOD concentration was "up trand" due to the flow at the NR3 (Nam-River) station. The COD concentration was "up trand" due to the flow at NR1 (Kyungho-River 1) and NR2 (Kyungho-River 2) located upstream of the Nam-River. The effect of influent flow on water quality varies according to each site and analysis item. Therefore, for the effective water quality management in the Nam-River, it is necessary to take measures to improve the water quality at the point where the water quality is continuously "up trand" during the study period.