Testing for trends on a regional scale: Beyond local significance

2021 ◽  
pp. 1-54
Author(s):  
Radan Huth ◽  
Martin Dubrovský
Keyword(s):  
Simple Procedure ◽  
Statistical Significance ◽  
Regional Scale ◽  
Synthetic Data ◽  
Kendall Test ◽  
Sign Test ◽  
Wide Margin ◽  
Null Distributions ◽  
Regression Tests ◽  
Local Significance

AbstractStudies detecting trends in climate elements typically concentrate on their local significance, ignoring the question on whether the significant local trends may or may not have occurred due to chance. The present paper fills this gap by examining several approaches to detecting statistical significance of trends defined on a grid, that is on a regional scale. To this end, we introduce a novel simple procedure of significance testing, which is based on counting signs of local trends (sign test), and compare it with five other approaches to testing collective significance of trends (counting, extended Mann-Kendall, Walker, fdr, and regression tests). Synthetic data are used to construct null distributions of trend statistics, to determine critical values of the tests, and to assess the performance of tests in terms of type II error. For lower values of spatial and temporal autocorrelations, the sign test and extended Mann-Kendall test perform slightly better than the counting test; these three tests outperform Walker, fdr, and regression tests by quite a wide margin. For high autocorrelations, which is a more realistic case, all tests become similar in their performance, with the exception of the regression test, which performs somewhat worse. Some tests cannot be used under specific conditions because of their construction: Walker and fdr tests for high temporal autocorrelations; sign test under high spatial autocorrelations.

Trend analysis of fire season length and extreme fire weather in North America between 1979 and 2015

2017 ◽  
Vol 26 (12) ◽  
pp. 1009 ◽  
Author(s):  
Piyush Jain ◽  
Xianli Wang ◽  
Mike D. Flannigan
Keyword(s):  
North America ◽  
Statistical Significance ◽  
Kendall Test ◽  
Fire Season ◽  
Fire Weather ◽  
Season Length ◽  
Eastern Canada ◽  
Reanalysis Dataset ◽  
Fire Weather Index ◽  
Extreme Fire

We have constructed a fire weather climatology over North America from 1979 to 2015 using the North American Regional Reanalysis dataset and the Canadian Fire Weather Index (FWI) System. We tested for the presence of trends in potential fire season length, based on a meteorological definition, and extreme fire weather using the non-parametric Theil–Sen slope estimator and Mann–Kendall test. Applying field significance testing (i.e. joint significance of multiple tests) allowed the identification of the locations of significant trends, taking into account spatial correlations. Fire season length was found to be increasing over large areas of North America, especially in eastern Canada and the south-western US, which is consistent with a later fire season end and an earlier fire season start. Both positive and negative trends in potential fire spread days and the 99th percentile of FWI occurred in Canada and the contiguous United States, although the trends of largest magnitude and statistical significance were mostly positive. In contrast, the proportion of trends with significant decreases in these variables were much lower, indicating an overall increase in extreme fire weather. The smaller proportion of significant positive trends found over Canada reflects the truncation of the time series, necessary because assimilation of precipitation observations over Canada ceased in the reanalysis post-2002.

The effect of 0.01% atropine on ocular axial elongation for myopia children: a meta-analysis

2021 ◽  
Author(s):  
Yan Yu ◽  
Jiasu Liu
Keyword(s):  
Publication Bias ◽  
Meta Analysis ◽  
Statistical Significance ◽  
Cochrane Library ◽  
Axial Elongation ◽  
Funnel Plots ◽  
Mean Differences ◽  
Q Statistic ◽  
Regression Tests ◽  
Review Manager

Objectives: This meta-analysis aimed to identify the therapeutic effect of 0.01% atropine with on ocular axial elongation for myopia children. Methods: We searched PubMed, Cochrane Library, and CBM databases from inception to July 2021. Meta-analysis was conducted using STATA version 14.0 and Review Manager version 5.3 softwares. We calculated the weighted mean differences(WMD) to analyze the change of ocular axial length (AL) between orthokeratology combined with 0.01% atropine (OKA) and orthokeratology (OA) alone. The Cochran's Q-statistic and I2 test were used to evaluate potential heterogeneity between studies. To evaluate the influence of single studies on the overall estimate, a sensitivity analysis was performed. We also performed sub group and meta-regression analyses to investigate potential sources of heterogeneity. We conducted Begger's funnel plots and Egger's linear regression tests to investigate publication bias. Results: Nine studies that met all inclusion criteria were included in this meta-analysis. A total of 191 children in OKA group and 196 children in OK group were assessed. The pooled summary WMD of AL change was -0.90(95%CI=-1.25~-0.55) with statistical significance(t=-5.03, p<0.01), which indicated there was obvious difference between OKA and OK in myopic children. Subgroup analysis also showed that OKA treatment resulted in significantly less axial elongation compared to OK treatment alone according to SER. We found no evidence for publication bias. Conclusions:  Our meta-analysis indicates 0.01% atropine atropine is effective in slowing axial elongation in myopia children with orthokeratology.

scholarly journals Evaluation of common variants in the CNR2 gene and its interaction with abdominal obesity for osteoporosis susceptibility in Chinese post-menopausal females

2019 ◽  
Vol 8 (11) ◽  
pp. 544-549
Author(s):  
W. Zheng ◽  
C. Liu ◽  
M. Lei ◽  
Y. Han ◽  
X. Zhou ◽  
...  
Keyword(s):  
Logistic Regression ◽  
Regression Model ◽  
Abdominal Obesity ◽  
Logistic Regression Model ◽  
Haplotype Analysis ◽  
Statistical Significance ◽  
Chinese Patients ◽  
Sign Test ◽  
Environment Interaction ◽  
Post Menopausal

Objectives The objective of this study was to investigate the association of four single-nucleotide polymorphisms (SNPs) of the cannabinoid receptor 2 (CNR2) gene, gene-obesity interaction, and haplotype combination with osteoporosis (OP) susceptibility. Methods Chinese patients with OP were recruited between March 2011 and December 2015 from our hospital. In this study, a total of 1267 post-menopausal female patients (631 OP patients and 636 control patients) were selected. The mean age of all subjects was 69.2 years (sd 15.8). A generalized multifactor dimensionality reduction (GMDR) model and logistic regression model were used to examine the interaction between SNP and obesity on OP. For OP patient-control haplotype analyses, the SHEsis online haplotype analysis software ( http://analysis.bio-x.cn/ ) was employed. Results The logistic regression model revealed that the C allele of rs2501431 and the G allele of rs3003336 were associated with increased OP risk, compared with those with wild genotype. However, no significant correlations were found when analyzing the association of rs4237 and rs2229579 with OP risk. The GMDR analysis suggested that the interaction model composed of two factors, rs3003336 and abdominal obesity (AO), was the best model with statistical significance (p-value from sign test (Psign) = 0.012), indicating a potential gene-environment interaction between rs3003336 and AO. Overall, the two-locus models had a cross-validation consistency of 10/10 and had a testing accuracy of 0.641. Abdominally obese subjects with the AG or GG genotype have the highest OP risk, compared with subjects with the AA genotype and normal waist circumference (WC) (odds ratio (OR) 2.23, 95% confidence interval (CI) 1.54 to 3.51). Haplotype analysis also indicated that the haplotype containing the rs3003336-G and rs2501431-C alleles was associated with a statistically increased OP risk. Conclusion Our results suggested that the C allele of rs2501431 and the G allele of rs3003336 of the CNR2 gene, interaction between rs3003336 and AO, and the haplotype containing the rs3003336-G and rs2501431-C alleles were all associated with increased OP risk. Cite this article: Bone Joint Res 2019;8:544–549.

scholarly journals SIMPLE, ROBUST, AND POWERFUL TESTS OF THE BREAKING TREND HYPOTHESIS

2009 ◽  
Vol 25 (4) ◽  
pp. 995-1029 ◽  
Author(s):  
David I. Harvey ◽  
Stephen J. Leybourne ◽  
A.M. Robert Taylor
Keyword(s):  
Time Series ◽  
Serial Correlation ◽  
Simple Procedure ◽  
Weighted Average ◽  
Local Power ◽  
Null Distributions ◽  
Optimal Tests ◽  
Univariate Time Series ◽  
Practical Usefulness ◽  
Standard Normal

In this paper we develop a simple procedure that delivers tests for the presence of a broken trend in a univariate time series that do not require knowledge of the form of serial correlation in the data and are robust as to whether the shocks are generated by an I(0) or an I(1) process. Two trend break models are considered: the first holds the level fixed while allowing the trend to break, while the latter allows for a simultaneous break in level and trend. For the known break date case, our proposed tests are formed as a weighted average of the optimal tests appropriate for I(0) and I(1) shocks. The weighted statistics are shown to have standard normal limiting null distributions and to attain the Gaussian asymptotic local power envelope, in each case regardless of whether the shocks are I(0) or I(1). In the unknown break date case, we adopt the method of Andrews (1993) and take a weighted average of the statistics formed as the supremum over all possible break dates, subject to a trimming parameter, in both the I(0) and I(1) environments. Monte Carlo evidence suggests that our tests are in most cases more powerful, often substantially so, than the robust broken trend tests of Sayginsoy and Vogelsang (2004). An empirical application highlights the practical usefulness of our proposed tests.

Spatio-temporal cluster analyses of landslides in Italy at national and regional scale

2020 ◽  
Author(s):  
Marj Tonini ◽  
Kim Romailler ◽  
Gaetano Pecoraro ◽  
Michele Calvello
Keyword(s):  
Cluster Analysis ◽  
Point Processes ◽  
Statistical Significance ◽  
Regional Scale ◽  
Regional Analysis ◽  
Scan Statistics ◽  
Economic Losses ◽  
Campania Region ◽  
Temporal Cluster ◽  
Spatio Temporal

&lt;p&gt;&lt;strong&gt;Keywords:&lt;/strong&gt; Landslides, FraneItalia, cluster analysis, spatio-temporal point process&lt;/p&gt;&lt;p&gt;In Italy landslides pose a significant and widespread risk, resulting in a large number of casualties and huge economic losses. Landslide inventories are critical to support investigations of where and when landslides have happened and may occur in the future, i.e. to establish reliable correlations between triggering factors and landslide occurrences. To deal with this issue, statistical methods originally developed for spatio-temporal stochastic point processes can be useful for identifying correlations between events in space and time and detecting a significant excess of cases within large landslide datasets.&lt;/p&gt;&lt;p&gt;In the present study, the authors propose an approach to analyze and visualize spatio-temporal clusters of landslides occurred in Italy in the period 2010-2017, considering the weather warning zones as territorial units. Besides, a regional analysis was conducted in Campania region considering the municipalities as territorial units. Data on landslide occurrences derived from the FraneItalia catalog, an inventory retrieved from online Italian news. The database contains 8931 landslides, grouped in 4231 single events and 938 areal events (records referring to multiple landslides triggered by the same cause in the same geographic area). Analyses were performed both annually, considering each year individually, and globally, considering the entire frame period. We applied the spatio-temporal scan statistics permutation model (STPSS, integrated in SaTScan&lt;sup&gt;TM&lt;/sup&gt; software), which allowed detecting clusters&amp;#8217; location and estimating their statistical significance. STPSS is based on cylindrical moving windows which scan the area across the space and in time counting the number of observed and expected occurrences and computing the likelihood ratio. The statistical inference (p-value) is evaluated by Monte Carlo sampling and finally the most likely clusters in the real and randomly generated datasets are compared.&lt;/p&gt;&lt;p&gt;Although more detailed analyses are required for the determination of cause-effect relationships among landslides and other variables, some relations with the local topographic and meteorological conditions can already be argued. At national scale, spatio-temporal clusters of landslides are mainly recurrent in two zones: the area enclosing Liguria Region &amp;#8211; Northern Tuscany at north-west and the area between Abruzzo and Molise regions at centre-east. During the year, landslide clusters are particularly abundant between October and March. as most of the events in the FraneItalia catalog are rainfall-induced, strongly influenced by seasonal rainfall patterns. Concerning the regional analysis, most of the clusters are located in the Lattari mountains, the Pizzo d&amp;#8217;Alvano massif and the Picentini mountains, areas highly susceptible to landslide occurrence due to geomorphological factors.&lt;/p&gt;&lt;p&gt;In conclusion, the application of spatio-temporal cluster analysis at various scale allowed the identification of frame periods with greater landslide activity. The question of whether this increase in activity depends climate conditions or topographic factors is still open and request further investigations.&lt;/p&gt;&lt;p&gt;REFERENCES&lt;/p&gt;&lt;p&gt;Calvello, M., Pecoraro, G. FraneItalia: a catalog of recent Italian landslides. &lt;em&gt;Geoenvironmental Disasters&lt;/em&gt;. 5: 13 (2018)&lt;/p&gt;&lt;p&gt;Tonini, M. &amp; Cama, M. Spatio-temporal pattern distribution of landslides causing damage in Switzerland. &lt;em&gt;Landslides&lt;/em&gt; 16 (2019)&lt;/p&gt;

scholarly journals SCALE AND LONG-TERM DYNAMICS OF OKA RIVER BASIN POLLUTION

2021 ◽  
Vol 26 (2) ◽  
pp. 40-53
Author(s):  
R. G. Dzhamalov ◽  
◽  
K. G. Vlasov ◽  
V. Y. Grigorev ◽  
K. G. Galagur ◽  
...  
Keyword(s):  
Water Quality ◽  
River Basin ◽  
Linear Trend ◽  
Statistical Significance ◽  
Rank Correlation ◽  
Correlation Coefficients ◽  
Kendall Test ◽  
Anthropogenic Load ◽  
Treated Wastewater

Introduction. This article addresses the long-term dynamics of Oka River basin pollution. The basin serves as the main source of drinking water and a receiver of wastewater from a number of regions in European Russia. Methods. We assessed the water quality by 12 main hydrochemical indicators and constructed maps of their distribution with a breakdown into two periods (1990–1999 and 2000–2017). The anthropogenic load along the section in the city of Gorbatov was determined. Spearman’s rank correlation coefficients and their statistical significance were calculated. Results. For 18 gauging stations with 25 and more years of observations, the magnitude of the linear trend (%/year) was estimated using the Theil–Sen estimator, and the statistical significance of the linear trend (Mann–Kendall test) was assessed for individual stations and the entire basin, using a modified Walker test. The runoff of pollutants from the urban territory was estimated between the sections upstream and downstream the cities in the upper reaches of the Oka River basin. The volumes of pollutants in the Oka River from the cities of Orel, Belev and Kaluga were determined for the period of 1990–2017. The calculations of the pollutant runoff, performed between the sections upstream and downstream the cities, made it possible to determine the role of the cities in the formation of point pollution in the upper reaches of the Oka River. The anthropogenic load along the length of the river in terms of the influx of chemicals varies from “low” to “high”. The load is largely due to the intake of pollutants since water bodies and watercourses serve as receivers of both treated and insufficiently treated wastewater from various enterprises. Conclusion. Almost throughout the basin, the water quality is under stress. The statistical analysis showed the existing relationship between a certain type of land use and the concentration of substances in surface waters. It was revealed that the self-cleaning capacity of the river is sufficient to prevent pollutants from accumulating along it.

scholarly journals Trends in frost days in Bosnia and Herzegovina

2017 ◽  
Vol 97 (1) ◽  
pp. 35-55
Author(s):  
Tatjana Popov ◽  
Slobodan Gnjato ◽  
Goran Trbic
Keyword(s):  
Time Series ◽  
Bosnia And Herzegovina ◽  
21St Century ◽  
Statistical Significance ◽  
Kendall Test ◽  
Plant Phenology ◽  
Climate System ◽  
Annual Number ◽  
Recent Trends ◽  
Banja Luka

The paper analyzes the recent trends in the occurrence of frost days in Bosnia and Herzegovina. Trends during the 1961-2015 periods were determined based on data from fourteen meteorological stations. MAKESENS procedure, which uses the nonparametric Mann-Kendall test and the nonparametric Sen?s method, was applied on time series of annual number of frost days to assess trends magnitude and its statistical significance. Given the results, negative and largely significant trends are present all over Bosnia and Herzegovina territory. The estimated decreasing trend was in the range of 2.1-6.4 days per decade. The percentile analysis of the annual number of frost days in Bosnia and Herzegovina suggests that a decreasing trend has become more pronounced since 1990s and particularly since the beginning of the 21st century. The observed downward trends were primarily a consequence of high negative trends in the coldest winter months - in January and December. The most prominent decrease in annual number of frost days was observed in Banja Luka, Bugojno, Zenica and Bjelasnica area. Further research on the effects of the determined trends in the frost occurrence on plants is necessary particularly due to the observed changes in plant phenology as a result of climate system warming.

scholarly journals The crossdip correction as a tool to improve imaging of crooked line seismic data: A case study from the post-glacial Burträsk fault, Sweden

2018 ◽  
Author(s):  
Ruth A. Beckel ◽  
Christopher Juhlin
Keyword(s):  
Seismic Data ◽  
Correction Term ◽  
Regional Scale ◽  
Synthetic Data ◽  
Shear Zones ◽  
Seismic Profile ◽  
Line Geometry ◽  
Processing Methods ◽  
Processing Scheme ◽  
Noise Tolerant

Abstract. Understanding the development of post-glacial faults and their associated seismic activity is crucial for risk assessment in Scandinavia. However, imaging these features and their geological environment is complicated due to special challenges of their hardrock setting, such as weak impedance contrasts, sometimes high noise levels and crooked acquisition lines. A crooked line geometry can cause time shifts that seriously de-focus and deform reflections containing a crossdip component. Advanced processing methods like swath 3D processing and 3D pre-stack migration can, in principle, handle the crooked line geometry, but may fail when the noise level is too high. For these cases, the effects of reflector crossdip can be compensated for by introducing a linear correction term into the standard processing flow. However, existing implementations of the crossdip correction rely on a slant stack approach which can, for some geometries, lead to a duplication of reflections. Here we present a module for the crossdip correction that avoids the reflection duplication problem by shifting the reflections prior to stacking. Based on tests with synthetic data, we developed an iterative processing scheme where a sequence consisting of crossdip correction, velocity analysis and DMO correction is repeated until the stacked image converges. Using our new module to reprocess a reflection seismic profile over the post-glacial Burträsk Fault in Northern Sweden increased the image quality significantly. Strike and dip information extracted from the crossdip analysis helped to interpret a set of southeast dipping reflections as shear zones belonging to the regional scale Burträsk Shear Zone (BSZ), implying that the BSZ itself is not a vertical, but a southeast dipping feature. Our results demonstrate that the crossdip correction is a highly useful alternative to more sophisticated processing methods for noisy datasets. This highlights the often underestimated potential of rather simple, but noise-tolerant methods, in processing hardrock seismic data.

scholarly journals UNDERSTANDING VERTICAL GROUND DISPLACEMENT FROM P-SBAS USING GETIS-ORD GI* STATISTIC

2021 ◽  
Author(s):  
Ignacio Barbero ◽  
Raúl Páez ◽  
Cristina Torrecillas
Keyword(s):  
Spatial Clustering ◽  
Statistical Significance ◽  
Regional Scale ◽  
Vertical Component ◽  
Spatial Statistic ◽  
Kinematic Study ◽  
Small Baseline Subset ◽  
Small Baseline ◽  
Grid Processing ◽  
Atmospheric Perturbations

The Differential Synthetic Aperture Radar Interferometric (DInSAR) algorithm has already shown its importance in volcanicmonitoring. However, it is limited by atmospheric perturbations or temporal decorrelation, implying the existence of lowcoherencerecords that must be discarded. In vast studied areas, with thousands of points unevenly distributed, theinterpretation of the results is usually complicated. This text presents an analysis of the vertical component variation onTenerife island (Canary Islands), from 2005 to 2010, using Getis-Ord Gi* spatial statistic on ENVISAT DinSAR images.The ascending and descending images have been processed using the Parallel Small BAseline Subset (P-SBAS)algorithm, within ESA Grid Processing on Demand cloud environment. From Line of Sight results of both tracks, the verticaldeformation speeds have been calculated over 72,207 points with high coherence (&gt; 0.7). Finally, the Gi* statistic hasbeen applied, obtaining a map with statistical significance, where the high values of Gi*, both positive and negative, implythe spatial clustering of likely ground movements. This map highlights areas with variable vertical kinematics on TenerifeIsland, contributing to understanding of its geodynamics. The displacements obtained coincide with previous studies, evenshowing possible new relationships between some phenomena that should be considered. The Gi* spatial statistic is anefficient and quick tool to extract information in a regional scale kinematic study.

scholarly journals The cross-dip correction as a tool to improve imaging of crooked-line seismic data: a case study from the post-glacial Burträsk fault, Sweden

Solid Earth ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 581-598
Author(s):  
Ruth A. Beckel ◽  
Christopher Juhlin
Keyword(s):  
Seismic Data ◽  
Correction Term ◽  
Regional Scale ◽  
Synthetic Data ◽  
Shear Zones ◽  
Seismic Profile ◽  
Line Geometry ◽  
Processing Methods ◽  
Processing Scheme ◽  
The Cross

Abstract. Understanding the development of post-glacial faults and their associated seismic activity is crucial for risk assessment in Scandinavia. However, imaging these features and their geological environment is complicated due to special challenges of their hardrock setting, such as weak impedance contrasts, often high noise levels and crooked acquisition lines. A crooked-line geometry can cause time shifts that seriously de-focus and deform reflections containing a cross-dip component. Advanced processing methods like swath 3-D processing and 3-D pre-stack migration can, in principle, handle the crooked-line geometry but may fail when the noise level is too high. For these cases, the effects of reflector cross-dip can be compensated for by introducing a linear correction term into the standard processing flow. However, existing implementations of the cross-dip correction rely on a slant stack approach which can, for some geometries, lead to a duplication of reflections. Here, we present a module for the cross-dip correction that avoids the reflection duplication problem by shifting the reflections prior to stacking. Based on tests with synthetic data, we developed an iterative processing scheme where a sequence consisting of cross-dip correction, velocity analysis and dip-moveout (DMO) correction is repeated until the stacked image converges. Using our new module to reprocess a reflection seismic profile over the post-glacial Burträsk fault in northern Sweden increased the image quality significantly. Strike and dip information extracted from the cross-dip analysis helped to interpret a set of southeast-dipping reflections as shear zones belonging to the regional-scale Burträsk Shear Zone (BSZ), implying that the BSZ itself is not a vertical but a southeast-dipping feature. Our results demonstrate that the cross-dip correction is a highly useful alternative to more sophisticated processing methods for noisy datasets. This highlights the often underestimated potential of rather simple but noise-tolerant methods in processing hardrock seismic data.

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