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Nonparametric Statistics (nonparametric + statistics)
Selected AbstractsMisprescription and misuse of one-tailed testsAUSTRAL ECOLOGY, Issue 4 2009CELIA M. LOMBARDI Abstract One-tailed statistical tests are often used in ecology, animal behaviour and in most other fields in the biological and social sciences. Here we review the frequency of their use in the 1989 and 2005 volumes of two journals (Animal Behaviour and Oecologia), their advantages and disadvantages, the extensive erroneous advice on them in both older and modern statistics texts and their utility in certain narrow areas of applied research. Of those articles with data sets susceptible to one-tailed tests, at least 24% in Animal Behaviour and at least 13% in Oecologia used one-tailed tests at least once. They were used 35% more frequently with nonparametric methods than with parametric ones and about twice as often in 1989 as in 2005. Debate in the psychological literature of the 1950s established the logical criterion that one-tailed tests should be restricted to situations where there is interest only in results in one direction. ,Interest' should be defined; however, in terms of collective or societal interest and not by the individual investigator. By this ,collective interest' criterion, all uses of one-tailed tests in the journals surveyed seem invalid. In his book Nonparametric Statistics, S. Siegel unrelentingly suggested the use of one-tailed tests whenever the investigator predicts the direction of a result. That work has been a major proximate source of confusion on this issue, but so are most recent statistics textbooks. The utility of one-tailed tests in research aimed at obtaining regulatory approval of new drugs and new pesticides is briefly described, to exemplify the narrow range of research situations where such tests can be appropriate. These situations are characterized by null hypotheses stating that the difference or effect size does not exceed, or is at least as great as, some ,amount of practical interest'. One-tailed tests rarely should be used for basic or applied research in ecology, animal behaviour or any other science. [source] Global analysis of reptile elevational diversityGLOBAL ECOLOGY, Issue 4 2010Christy M. McCain ABSTRACT Aim, Latitudinal- and regional-scale studies of reptile diversity suggest a predominant temperature effect, unlike many other vertebrate richness patterns which tend to be highly correlated with both temperature and water variables. Here I examine montane gradients in reptile species richness with separate analyses of snakes and lizards from mountains around the world to assess a predominant temperature effect and three additional theories of diversity, including a temperature,water effect, the species,area effect and the mid-domain effect (MDE). Location, Twenty-five elevational gradients of reptile diversity from temperate, tropical and desert mountains in both hemispheres, spanning 10.3° N to 46.1° N. Methods, Elevational gradients in reptile diversity are based on data from the literature. Of the 63 data sets found or compiled, only those with a high, unbiased sampling effort were used in analyses. Twelve predictions and three interactions of diversity theory were tested using nonparametric statistics, linear regressions and multiple regression with the Akaike information criterion (AIC). Results, Reptile richness and, individually, snake and lizard richness on mountains followed four distinct patterns: decreasing, low-elevation plateaus, low-elevation plateaus with mid-elevation peaks, and mid-elevation peaks. Elevational reptile richness was most strongly correlated with temperature. The temperature effect was mediated by precipitation; reptile richness was more strongly tied to temperature on wet gradients than on arid gradients. Area was a secondary factor of importance, whereas the MDE was not strongly associated with reptile diversity on mountains. Main conclusions, Reptile diversity patterns on mountains did not follow the predicted temperature,water effect, as all diversity patterns were found on both wet and dry mountains. But the influence of precipitation on the temperature effect most likely reflects reptiles' use of radiant heat sources (sunning opportunities) that are more widespread on arid mountains than wet mountains due to lower humidity, sparser vegetation and less cloud cover across low and intermediate elevations. [source] Range Unit-Root (RUR) Tests: Robust against Nonlinearities, Error Distributions, Structural Breaks and OutliersJOURNAL OF TIME SERIES ANALYSIS, Issue 4 2006Felipe Aparicio Abstract., Since the seminal paper by Dickey and Fuller in 1979, unit-root tests have conditioned the standard approaches to analysing time series with strong serial dependence in mean behaviour, the focus being placed on the detection of eventual unit roots in an autoregressive model fitted to the series. In this paper, we propose a completely different method to test for the type of long-wave patterns observed not only in unit-root time series but also in series following more complex data-generating mechanisms. To this end, our testing device analyses the unit-root persistence exhibited by the data while imposing very few constraints on the generating mechanism. We call our device the range unit-root (RUR) test since it is constructed from the running ranges of the series from which we derive its limit distribution. These nonparametric statistics endow the test with a number of desirable properties, the invariance to monotonic transformations of the series and the robustness to the presence of important parameter shifts. Moreover, the RUR test outperforms the power of standard unit-root tests on near-unit-root stationary time series; it is invariant with respect to the innovations distribution and asymptotically immune to noise. An extension of the RUR test, called the forward,backward range unit-root (FB-RUR) improves the check in the presence of additive outliers. Finally, we illustrate the performances of both range tests and their discrepancies with the Dickey,Fuller unit-root test on exchange rate series. [source] Emergency Medicine Career Choice: A Profile of Factors and Influences from the Association of American Medical Colleges (AAMC) Graduation QuestionnairesACADEMIC EMERGENCY MEDICINE, Issue 6 2009Jeremy S. Boyd Abstract Objectives:, This study sought to account for trends in medical student specialty choice by examining the importance of lifestyle factors. Emergency medicine (EM) is among several medical specialties classified as having a "controllable lifestyle." The primary objective of this study was to determine if medical students choosing careers in EM have a different profile of influences, values, and expectations from students choosing other specialties or specialty groups. Of secondary interest was how much lifestyle influenced students choosing EM compared to students choosing controllable lifestyle (CL) specialties. Methods:, Using data from the 2005 and 2006 Association of American Medical Colleges (AAMC) graduation questionnaire (GQ) supplemental surveys, we grouped responses according to desired specialty choice: EM (n = 963), CL (n = 3,681), primary care (PC; n = 3,191), or surgical specialty (SS; n = 1,694). The survey requires students to rate the influence of nine specific factors in determining their specialty choice: lifestyle, competitiveness, high level of educational debt, mentors and role models, options for fellowship training, salary expectations, length of residency training, family expectations, and medical school career planning activities. Using one-way analysis of variance (ANOVA) and nonparametric statistics, we assessed responses among the four subgroups for differences in the importance attributed to these factors. Results:, A total of 13,440 students completed the two supplemental surveys of the GQ. Of these students, 9,529 identified a specialty choice that fell within one of the four comparison groups and were included in the analysis. Compared to other specialty groups, students choosing EM reported lifestyle and length of residency as strong influences, while attributing less influence to mentors and options for fellowship training. Conclusions:, Students choosing a career in EM have distinctly different priorities and influences than students entering PC and SS. The profile of students who choose EM is very similar to those choosing traditional CL specialties. A more thorough understanding of the values and priorities that shape medical student career selection may allow educators to provide better career counseling. [source] | ||||||||||