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Significance Testing (significance + testing)

Distribution by Scientific Domains

Life Sciences	40%
Humanities and Social Sciences	20%
Medical Sciences	13%

Selected Abstracts

A Communication Researchers' Guide to Null Hypothesis Significance Testing and Alternatives

HUMAN COMMUNICATION RESEARCH, Issue 2 2008
Timothy R. Levine
This paper offers a practical guide to use null hypotheses significance testing and its alternatives. The focus is on improving the quality of statistical inference in quantitative communication research. More consistent reporting of descriptive statistics, estimates of effect size, confidence intervals around effect sizes, and increasing the statistical power of tests would lead to needed improvements over current practices. Alternatives including confidence intervals, effect tests, equivalence tests, and meta-analysis are discussed. Résumé Le guide du test de signification basé sur l,hypothèse nulle et de ses alternatives, à l'usage des chercheurs en communication Cet article offre un guide pratique pour l,utilisation du test de signification basé sur l'hypothèse nulle (NHST) et de ses alternatives. Il se concentre sur la manière d,améliorer la qualité de l'inférence statistique dans la recherche quantitative en communication. Une divulgation plus cohérente de la statistique descriptive, une évaluation de l,ampleur de l'effet, des intervalles de confiance autour de l,ampleur de l'effet et une augmentation de l,efficacité statistique des tests mèneraient à de nécessaires améliorations des pratiques actuelles. Des alternatives sont commentées, dont les intervalles de confiance, les tests d'effet, les tests d'équivalence et la méta-analyse. Abstract Anleitung und Alternativen zum Nullhypothesen-Signifikanztesten für Kommunikationsforscher Dieser Artikel bietet eine praktische Anleitung zum Gebrauch von Nullhypothesen-Signifikanztests und zu möglichen Alternativen. Der Fokus des Artikels liegt dabei auf der Qualitätsverbesserung von statistischen Inferenzschlüssen in der quantitativen Kommunikationsforschung. Eine konsistentere Dokumentation und Offenlegung von deskriptiver Statistik, Effektgrößen, Konfidenzintervallen der Effektgrößen und die Verbesserung der statistischen Power von Tests würden zu einer Optimierung der bislang üblichen Praxis führen. Alternativen wie Konfidenzintervalle, Effekttests, Äquivalenztests und Meta-Analysen werden diskutiert. Resumen Una Guía para los Investigadores de Comunicación sobre la Puesta a Prueba de la Significancia de la Hipótesis Nula y sus Alternativas Este artículo ofrece una guía práctica para el uso de la puesta a prueba de la significancia (NHST) de las hipótesis nulas y sus alternativas. El enfoque se centra en mejorar la calidad de la inferencia estadística de la investigación de comunicación cuantitativa. Reportes estadísticos descriptivos más consistentes, estimaciones del efecto de tamaño, intervalos de confianza alrededor del efecto de tamaño, y el incremento del poder estadístico de las pruebas podrían conducir hacia mejoras necesarias de las prácticas corrientes. Las alternativas, incluyendo intervalos de confianza, pruebas de efecto, pruebas de equivalencia, y meta-análisis, son discutidas. ZhaiYao Yo yak [source]

Significance testing of synergistic/antagonistic, dose level-dependent, or dose ratio-dependent effects in mixture dose-response analysis

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2005
Martijs J. Jonker
Abstract In ecotoxicology, the state of the art for effect assessment of chemical mixtures is through multiple dose,response analysis of single compounds and their combinations. Investigating whether such data deviate from the reference models of concentration addition and/or independent action to identify overall synergism or antagonism is becoming routine. However, recent data show that more complex deviation patterns, such as dose ratio,dependent deviation and dose level,dependent deviation, need to be addressed. For concentration addition, methods to detect such deviation patterns exist, but they are stand-alone methods developed separately in literature, and conclusions derived from these analyses are therefore difficult to compare. For independent action, hardly any methods to detect such deviations from this reference model exist. This paper describes how these well-established mixture toxicity principles have been incorporated in a coherent data analysis procedure enabling detection and quantification of dose level,and dose ratio,specific synergism or antagonism from both the concentration addition and the independent action models. Significance testing of which deviation pattern describes the data best is carried out through maximum likelihood analysis. This analysis procedure is demonstrated through various data sets, and its applicability and limitations in mixture research are discussed. [source]

The analysis of indexed astronomical time series , X. Significance testing of O,C data

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
Chris Koen
ABSTRACT It is assumed that O,C (,observed minus calculated') values of periodic variable stars are determined by three processes, namely measurement errors, random cycle-to-cycle jitter in the period, and possibly long-term changes in the mean period. By modelling the latter as a random walk, the covariances of all O,C values can be calculated. The covariances can then be used to estimate unknown model parameters, and to choose between alternative models. Pseudo-residuals which could be used in model fit assessment are also defined. The theory is illustrated by four applications to spotted stars in eclipsing binaries. [source]

Prevention programs in the 21st century: what we do not discuss in public

ADDICTION, Issue 4 2010
Harold Holder
ABSTRACT Prevention research concerning alcohol, tobacco and other drugs faces a number of challenges as the scientific foundation is strengthened for the future. Seven issues which the prevention research field should address are discussed: lack of transparency in analyses of prevention program outcomes, lack of disclosure of copyright and potential for profit/income during publication, post-hoc outcome variable selection and reporting only outcomes which show positive and statistical significance at any follow-up point, tendency to evaluate statistical significance only rather than practical significance as well, problem of selection bias in terms of selecting subjects and limited generalizability, the need for confirmation of outcomes in which only self-report data are used and selection of appropriate statistical distributions in conducting significance testing. In order to establish a solid scientific base for alcohol, tobacco and drug prevention, this paper calls for discussions, disclosures and debates about the above issues (and others) as essential. In summary, the best approach is always transparency. [source]

The relationship between baseline value and its change: problems in categorization and the proposal of a new method

EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 4 2005
Yu-Kang Tu
Oral health researchers have shown great interest in the relationship between the initial status of diseases and subsequent changes following treatment. Two main approaches have been adopted to provide evidence of a positive association between baseline values and their changes following treatment. One approach is to use correlation or regression to test the relationship between baseline measurements and subsequent change (correlation/regression approach). The second approach is to categorize the lesions into subgroups, according to threshold values, and subsequently compare the treatment effects across the two (or more) subgroups (categorization approach). However, the correlation/regression approach suffers a methodological weakness known as mathematical coupling. Consequently, the statistical procedure of testing the null hypothesis becomes inappropriate. Categorization seems to avoid the problem of mathematical coupling, although it still suffers regression to the mean. We show, first, how the appropriate null hypothesis may be established to analyze the relationship between baseline values and change in the correlation approach and, second, we use computer simulations to investigate the impact of regression to the mean on the significance testing of the differences in the average treatment effects (or average baseline values) in the categorization approach. Data available from previous literature are reanalyzed by testing the appropriate null hypotheses and the results are compared to those from testing the usual (incorrect) null hypothesis. The results indicate that both the correlation and categorization approaches can give rise to misleading conclusions and that more appropriate methods, such as Oldham's method and our new approach of deriving the correct null hypothesis, should be adopted. [source]

A Communication Researchers' Guide to Null Hypothesis Significance Testing and Alternatives

Making subjective judgments in quantitative studies: The importance of using effect sizes and confidence intervals

HUMAN RESOURCE DEVELOPMENT QUARTERLY, Issue 2 2006
Jamie L. Callahan
At least twenty-three journals in the social sciences purportedly require authors to report effect sizes and, to a much lesser extent, confidence intervals; yet these requirements are rarely clear in the information for contributors. This article reviews some of the literature criticizing the exclusive use of null hypothesis significance testing (NHST) and briefly highlights the state of NHST reporting in social science journals, including Human Resource Development Quarterly. Included are an overview of effect sizes and confidence intervals,their definitions, a brief historical review, and an argument regarding their importance. The article concludes with recommendations for changing the culture of quantitative research within human resource development (HRD) to more systematically reporting effect sizes and confidence intervals as supplements to NHST findings. [source]

Intra-seasonal rainfall characteristics and their importance to the seasonal prediction problem

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2002
Warren J. Tennant
Abstract Daily station rainfall data in South Africa from 1936 to 1999 are combined into homogeneous rainfall regions using Ward's clustering method. Various rainfall characteristics are calculated for the summer season, defined as December to February. These include seasonal rainfall total, region-average number of station rain days exceeding 1 and 20 mm, region-average of periods between rain days at stations >1 and >20 mm, region-average of wet spell length (sequential days of station rainfall >1 and >20 mm), correlation of daily station rainfall within a region and correlation of seasonal station rainfall anomalies within a region. Rank-ordered rainfall characteristic data generally form an s-shaped curve, and significance testing of discontinuities in these curves suggests that normal rainfall conditions in South Africa consist of a combined middle three quintiles separated from the outer quintiles, rather than the traditional middle tercile. The relationships between the various rainfall characteristics show that seasons with a high total rainfall generally have a higher number of heavy rain days (>20 mm) and not necessarily an increase in light rain days. The length of the period between rain days has a low correlation to season totals, demonstrating that seasons with a high total rainfall may still contain prolonged dry periods. These additional rainfall characteristics are important to end-users, and the analysis undertaken here offers a valuable starting point for seeking physical relationships between rainfall characteristics and the general circulation. Preliminary studies show that the vertical mean wind is related to rainfall characteristics in South Africa. Given that general circulation models capture this part of the circulation adequately, seasonal forecasts of rainfall characteristics become plausible. Copyright © 2002 Royal Meteorological Society. [source]

Pelvic growth: Ontogeny of size and shape sexual dimorphism in rat pelves

JOURNAL OF MORPHOLOGY, Issue 1 2007
S. Berdnikovs
Abstract The mammalian pelvis is sexually dimorphic with respect to both size and shape. Yet little is known about the differences in postnatal growth and bone remodeling that generate adult sexual dimorphism in pelvic bones. We used Sprague-Dawley laboratory rats (Rattus norvegicus), a species that exhibits gross pelvic size and shape dimorphism, as a model to quantify pelvic morphology throughout ontogeny. We employed landmark-based geometric morphometrics methodology on digitized landmarks from radiographs to test for sexual dimorphism in size and shape, and to examine differences in the rates, magnitudes, and directional patterns of shape change during growth. On the basis of statistical significance testing, the sexes became different with respect to pelvic shape by 36 days of age, earlier than the onset of size dimorphism (45 days), although visible shape differences were observed as early as at 22 days. Males achieved larger pelvic sizes by growing faster throughout ontogeny. However, the rates of shape change in the pelvis were greater in females for nearly all time intervals scrutinized. We found that trajectories of shape change were parallel in the two sexes until age of 45 days, suggesting that both sexes underwent similar bone remodeling until puberty. After 45 days, but before reproductive maturity, shape change trajectories diverged because of specific changes in the female pelvic shape, possibly due to the influence of estrogens. Pattern of male pelvic bone remodeling remained the same throughout ontogeny, suggesting that androgen effects on male pelvic morphology were constant and did not contribute to specific shape changes at puberty. These results could be used to direct additional research on the mechanisms that generate skeletal dimorphisms at different levels of biological organization. J. Morphol., 2006. © 2006 Wiley-Liss, Inc. [source]

USING NETWORK ANALYSIS TO CHARACTERIZE FOREST STRUCTURE

NATURAL RESOURCE MODELING, Issue 2 2008
MICHAEL M. FULLER
Abstract Network analysis quantifies different structural properties of systems of interrelated parts using a single analytical framework. Many ecological phenomena have network-like properties, such as the trophic relationships of food webs, geographic structure of metapopulations, and species interactions in communities. Therefore, our ability to understand and manage such systems may benefit from the use of network-analysis techniques. But network analysis has not been applied extensively to ecological problems, and its suitability for ecological studies is uncertain. Here, we investigate the ability of network analysis to detect spatial patterns of species association in a tropical forest. We use three common graph-theoretic measures of network structure to quantify the effect of understory tree size on the spatial association of understory species with trees in the canopy: the node degree distribution (NDD), characteristic path length (CPL), and clustering coefficient (CC). We compute the NDD, CPL, and CC for each of seven size classes of understory trees. For significance testing, we compare the observed values to frequency distributions of each statistic computed from randomized data. We find that the ability of network analysis to distinguish observed patterns from those representing randomized data strongly depends on which aspects of structure are investigated. Analysis of NDD finds no significant difference between random and observed networks. However, analysis of CPL and CC detected nonrandom patterns in three and one of the seven size classes, respectively. Network analysis is a very flexible approach that holds promise for ecological studies, but more research is needed to better understand its advantages and limitations. [source]

Study of GM immunoglobulin allotypic system in Berbers and Arabs from Morocco

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 1 2006
C. Coudray
The GM immunoglobulin allotype polymorphism was investigated in four Moroccan populations: three Berber groups from Khenifra (Middle Atlas), Amizmiz (High Atlas), and Bouhria (Beni Snassen) and one Arabic-speaking sample from the Doukkala area (Abda, Chaouia, Doukkali, and Tadla districts in south-central Morocco). In order to characterize the genetic relationships between the populations, our results were compared with those obtained for other North African groups (from Morocco, Algeria, Tunisia, and Niger) and for Middle-East Africans, sub-Saharans, and Southwest Europeans. Based on GM haplotype frequencies, Factorial Correspondence Analyses, FST significance testing, and hierarchical analyses of variance were performed. Our results reveal that Moroccan populations have heterogeneous GM profiles with high frequencies of GM haplotypes in Europeans (from 76% for Doukkala to 88% for Bouhria) and relatively high frequencies of GM haplotypes in sub-Saharans (from 11% for Bouhria to 23% for Amizmiz). The genetic diversity observed among Moroccans is not significantly correlated with either geographic or linguistic differentiation. In spite of their cultural and historical differentiation, we did not discover any significant genetic differences between Berbers and Arabic-speakers from Morocco. However, when large geographical areas are considered, our population samples are integrated in the North African GM variation, significantly distant from sub-Saharan groups but with a close relationship with Southwest European populations. Am. J. Hum. Biol. 18:23,34, 2006. © 2005 Wiley-Liss, Inc. [source]

Lack of statistical significance

PSYCHOLOGY IN THE SCHOOLS, Issue 5 2007
Thomas J. Kehle
Criticism has been leveled against the use of statistical significance testing (SST) in many disciplines. However, the field of school psychology has been largely devoid of critiques of SST. Inspection of the primary journals in school psychology indicated numerous examples of SST with nonrandom samples and/or samples of convenience. In this article we present an argument against SST and its consequent p values in favor of the use of confidence intervals and effect sizes. Further, we present instances of common errors that impede cumulative knowledge in the literature related to school psychology. © 2007 Wiley Periodicals, Inc. Psychol Schs 44: 417,422, 2007. [source]

Nonparametric smoothing using state space techniques

THE CANADIAN JOURNAL OF STATISTICS, Issue 1 2001
Patrick E. Brown
Abstract The authors examine the equivalence between penalized least squares and state space smoothing using random vectors with infinite variance. They show that despite infinite variance, many time series techniques for estimation, significance testing, and diagnostics can be used. The Kalman filter can be used to fit penalized least squares models, computing the smoothed quantities and related values. Infinite variance is equivalent to differencing to stationarity, and to adding explanatory variables. The authors examine constructs called "smoothations" which they show to be fundamental in smoothing. Applications illustrate concepts and methods. Les auteurs examinent l'équivalence entre les moindres carrés pénalisés et le lissage de l'espace d'états au moyen de vecteurs aléatoires à variance infinie. Ils montrent que malgré le problème de variance infinie, plusieurs techniques de diagnostic, d'estimation et de test de signification propres aux chroniques restent valables. Le filtre de Kalman permet d'évaluer les modèles des moindres carrés pénalisés en fournissant entre autres des valeurs lissées. La variance infinie est équivalente à la différenciation à des fins de stationnarité et à l'ajout de variables explicatives. Les auteurs étudient en outre des quantités appelées "lissations," dont ils montrent l'importance pour le lissage. Des applications illustrent les méthodes et procédures décrites. [source]

Critical thresholds associated with habitat loss: a review of the concepts, evidence, and applications

BIOLOGICAL REVIEWS, Issue 1 2010
Trisha L. Swift
A major conservation concern is whether population size and other ecological variables change linearly with habitat loss, or whether they suddenly decline more rapidly below a "critical threshold" level of habitat. The most commonly discussed explanation for critical threshold responses to habitat loss focus on habitat configuration. As habitat loss progresses, the remaining habitat is increasingly fragmented or the fragments are increasingly isolated, which may compound the effects of habitat loss. In this review we also explore other possible explanations for apparently nonlinear relationships between habitat loss and ecological responses, including Allee effects and time lags, and point out that some ecological variables will inherently respond nonlinearly to habitat loss even in the absence of compounding factors. In the literature, both linear and nonlinear ecological responses to habitat loss are evident among simulation and empirical studies, although the presence and value of critical thresholds is influenced by characteristics of the species (e.g. dispersal, reproduction, area/edge sensitivity) and landscape (e.g. fragmentation, matrix quality, rate of change). With enough empirical support, such trends could be useful for making important predictions about species' responses to habitat loss, to guide future research on the underlying causes of critical thresholds, and to make better informed management decisions. Some have seen critical thresholds as a means of identifying conservation targets for habitat retention. We argue that in many cases this may be misguided, and that the meaning (and utility) of a critical threshold must be interpreted carefully and in relation to the response variable and management goal. Despite recent interest in critical threshold responses to habitat loss, most studies have not used any formal statistical methods to identify their presence or value. Methods that have been used include model comparisons using Akaike information criterion (AIC) or t -tests, and significance testing for changes in slope or for polynomial effects. The judicious use of statistics to help determine the shape of ecological relationships would permit greater objectivity and more comparability among studies. [source]