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Trend Models (trend + models)

Distribution by Scientific Domains

Mathematics and Statistics	50%

Selected Abstracts

Modified median polish kriging and its application to the Wolfcamp,Aquifer data

ENVIRONMETRICS, Issue 8 2001
Olaf Berke
Abstract In geostatistics, spatial data will be analyzed that often come from irregularly distributed sampling locations. Interest is in modelling the data, i.e. estimating distributional parameters, and then to predict the phenomenon under study at unobserved sites within the corresponding sampling domain. The method of universal kriging for spatial prediction was introduced to cover the problem of spatial trend effects. This is done by incorporating linear trend models, e.g. polynomial functions of the spatial co-ordinates. However, universal kriging is sensitive to additive outliers. An outlier resistant method for spatial prediction is median polish kriging. Both methods have certain advantages but also some drawbacks. Here, universal kriging and median polish kriging will be combined to the robust spatial prediction method called modified median polish kriging. An example illustrates the method of modified median polish kriging along with piezometric-head data from the Wolfcamp,Aquifer. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Forecasting obesity trends in England

JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2009
Terence C. Mills
Summary., Forecasts of trends in obesity in England for 2010 are produced by treating the available data, which contain the proportions of the population, categorized by age and sex, falling into different body mass index ranges, as compositional data sets, so that the implicit simplex restrictions are automatically satisfied. Forecasts are calculated by using linear trend models for the log-ratio transformations and are accompanied by prediction regions. The advantages of treating data on proportions compositionally are emphasized and compared with forecasts that have been obtained by ignoring this restriction. [source]

Distinguishing between trend-break models: method and empirical evidence

THE ECONOMETRICS JOURNAL, Issue 2 2001
Chih-Chiang Hsu
We demonstrate that in time trend models, the likelihood-based tests of partial parameter stability have size distortions and cannot be applied to detect the changing parameter. A two-step procedure is then proposed to distinguish between different trend-break models. This procedure involves consistent estimation of break dates and properly-sized tests for changing coefficient. In the empirical study of the Nelson-Plosser data set, we find that the estimated change points and trend-break specifications resulting from the proposed procedure are quite different from those of Perron (1989, 1997), Chu and White (1992), and Zivot and Andrews (1992). In another application, our procedure provides formal support for the conclusion of Ben-David and Papell (1995) that real per capita GDPs of most OECD countries exhibit a slope change in trend. [source]

Why Is Late-Life Disability Declining?

THE MILBANK QUARTERLY, Issue 1 2008
ROBERT F. SCHOENI
Context: Late-life disability has been declining in the United States since the 1980s. This study provides the first comprehensive investigation into the reasons for this trend. Methods: The study draws on evidence from two sources: original data analyses and reviews of existing studies. The original analyses include trend models of data on the need for help with daily activities and self-reported causes of such limitations for the population aged seventy and older, based on the National Health Interview Surveys from 1982 to 2005. Findings: Increases in the use of assistive and mainstream technologies likely have been important, as have declines in heart and circulatory conditions, vision, and musculoskeletal conditions as reported causes of disability. The timing of the improvements in these conditions corresponds to the expansion in medical procedures and pharmacologic treatment for cardiovascular disease, increases in cataract surgery, increases in knee and joint replacements, and expansion of medications for arthritic and rheumatic conditions. Greater educational attainment, declines in poverty, and declines in widowhood also appear to have contributed. Changes in smoking behavior, the population's racial/ethnic composition, the proportion of foreign born, and several specific conditions were eliminated as probable causes. Conclusions: The substantial reductions in old-age disability between the early 1980s and early 2000s are likely due to advances in medical care as well as changes in socioeconomic factors. More research is needed on the influence of health behaviors, the environment, and early- and midlife factors on trends in late-life disability. [source]