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Nonparametric Statistical Tests (nonparametric + statistical_test)

Distribution by Scientific Domains

Medical Sciences	44%

Selected Abstracts

Testing Features of Graphical DIF: Application of a Regression Correction to Three Nonparametric Statistical Tests

JOURNAL OF EDUCATIONAL MEASUREMENT, Issue 4 2006
Daniel M. Bolt
Inspection of differential item functioning (DIF) in translated test items can be informed by graphical comparisons of item response functions (IRFs) across translated forms. Due to the many forms of DIF that can emerge in such analyses, it is important to develop statistical tests that can confirm various characteristics of DIF when present. Traditional nonparametric tests of DIF (Mantel-Haenszel, SIBTEST) are not designed to test for the presence of nonuniform or local DIF, while common probability difference (P-DIF) tests (e.g., SIBTEST) do not optimize power in testing for uniform DIF, and thus may be less useful in the context of graphical DIF analyses. In this article, modifications of three alternative nonparametric statistical tests for DIF, Fisher's ,2test, Cochran's Z test, and Goodman's U test (Marascuilo & Slaughter, 1981), are investigated for these purposes. A simulation study demonstrates the effectiveness of a regression correction procedure in improving the statistical performance of the tests when using an internal test score as the matching criterion. Simulation power and real data analyses demonstrate the unique information provided by these alternative methods compared to SIBTEST and Mantel-Haenszel in confirming various forms of DIF in translated tests. [source]

Measurement of Viscosity of Densifying Glass-Based Systems by Isothermal Cyclic Loading Dilatometry

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2004
Aravind Mohanram
This study describes the isothermal cyclic loading dilatometry (ICLD) technique to measure the viscosity of glass-based materials. We demonstrate its merit relative to constant-load techniques in minimizing the stress history effects (changes in shrinkage anisotropy and sample microstructure) that arise due to the application of an external load. A constant-load test overestimates the viscosity by an order of magnitude compared with a cyclic load test. To obtain accurate viscosity data, maximum loading rates and longer unloading periods are desirable as they reduce effects of shrinkage anisotropy on viscosity values. Representative data for a low-temperature cofired ceramic (LTCC) material are reported. Nonparametric statistical tests revealed insignificant differences between the viscosity data sets at 5% significance level and thus indicate good reproducibility of the testing methodology. [source]

Skin hydration and transepidermal water loss in patients with a history of sulfur mustard contact: a case,control study

JOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 8 2009
Seyyed Masoud Davoudi
Abstract Background,, Skin lesions are among the most common complications of contact with sulfur mustard. Objective,, This study was aimed to measure skin water content and transepidermal water loss (TEWL) in patients with a history of sulfur mustard contact. Methods,, Three hundred ten male participants were included in this study: 87 (28.1%) sulfur mustard,exposed patients with current skin lesions (group 1), 71 (22.9%) sulfur mustard,exposed patients without skin lesions (group 2), 78 (25.2%) patients with dermatitis (group 3) and 74 (23.8%) normal controls (group 4) The water content and TEWL of skin was measured at four different locations of the body: forehead, suprasternal, palm and dorsum of hand. Nonparametric statistical tests (Kruskal,Wallis) were used to compare the four groups, and P < 0.05 was considered statistically significant. Results,, The mean age of participants were 44.0 ± 6.7, 41.9 ± 5.9, 43.8 ± 9.3 and 44.8 ± 8.9 years in groups 1 to 4, respectively (P = 0.146). Xerosis, post-lesional hyperpigmentation and lichenification were significantly more common in either sulfur mustard,exposed participants or non-exposed participants with dermatitis (P < 0.05). Skin hydration was higher in subjects with sulfur mustard contact than in non-injured participants (P < 0.05) in the dorsum and palm of hands and forehead. TEWL was significantly higher in participants only in suprasternal area and dorsum of hand. Conclusion,, Contact with sulfur mustard agent can alter biophysical properties of the skin-especially the function of stratum corneum as a barrier to water loss-several years after exposure. Conflicts of interest None declared. [source]

Use of nonparametric statistical tests in defining the number of periods to include in an intertemporal DEA analysis

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2007
Taraneh Sowlati
Abstract In any type of intertemporal efficiency analyses either locally or globally, units in different periods are compared against each other, and therefore it is assumed that no frontier shift exists within the periods of study. This assumption extends in window analysis to each window. In almost all studies in the past, the number of periods included in an intertemporal data envelopment analysis or the width of a window in a window analysis is determined without validating this assumption analytically. This is a problem which has not been fully addressed in the literature. This paper presents a new approach using nonparametric statistical tests to examine a frontier shift and determine the number of periods to include in an intertemporal analysis. The case of sawmills in Vancouver, Canada is used to demonstrate how to apply this new approach. [source]

Testing Features of Graphical DIF: Application of a Regression Correction to Three Nonparametric Statistical Tests

A new classification of HLA,DRB1 alleles differentiates predisposing and protective alleles for rheumatoid arthritis structural severity

ARTHRITIS & RHEUMATISM, Issue 2 2006
Pierre-Antoine Gourraud
Objective A new classification of HLA,DRB1 alleles supporting the shared epitope hypothesis of rheumatoid arthritis (RA) susceptibility was recently introduced. We investigated the relevance of this classification in terms of the structural severity of RA. Methods The study group comprised 144 patients who were included in a prospective longitudinal cohort of French Caucasoid patients with early RA. Progression of the total radiographic damage score (Sharp/van der Heijde method) was used to quantify the structural severity of RA after 4 years of followup. HLA,DRB1 typing and subtyping were performed by polymerase chain reaction, using a panel of sequence-specific oligonucleotide probes. HLA,DRB1 alleles were classified according to the above-mentioned new system. The association between the HLA,DRB1 allele groups (S1, S2, S3P, S3D, and X) and the structural severity of RA was analyzed with nonparametric statistical tests. Results The presence of S2 alleles (HLA,DRB1*0401 and HLA,DRB1*1303) was associated with severe forms of RA (P = 0.004); a significant dose effect was observed (P = 0.01). The presence of S3D alleles (HLA,DRB1*11001, HLA,DRB1*1104, HLA,DRB1*12, and HLA,DRB1*16) was associated with benign forms of RA (P < 0.0001), and a significant dose effect was observed (P < 0.01). Conclusion The studied classification of HLA,DRB1 alleles is relevant in terms of RA outcomes. Compared with a previously described classification system, this system differentiates predisposing (S2) and protective (S3D) alleles for RA structural severity, which, respectively, correspond to KRRAA and DRRAA amino acid patterns at position 70,74 of the third hypervariable region of the HLA,DR, chain. [source]

The presence of dominant T-cell clones in peripheral blood of patients with collagen vascular disorders: a prospective study of 97 cases

BRITISH JOURNAL OF DERMATOLOGY, Issue 3 2006
O. Dereure
Summary Background, T-lymphocyte dysfunction has been seldom investigated in collagen vascular disorders. The search for dominant T-cell clones has been scarcely reported, although the presence of such clones might be expected in disorders showing immune responses directed against a variety of autoantigens. Objectives, We conducted a systematic search for dominant T-cell clones in peripheral blood in patients with collagen vascular disorders. Patients and methods, Ninety-seven patients with collagen vascular disorders were studied (7 cutaneous and 38 systemic lupus erythematosus; 8 multiple morphea; 12 regional scleroderma; 32 systemic sclerosis of the CREST type). A dominant T-cell clone was searched for in peripheral blood by polymerase chain reaction targeting the T-cell receptor , chain followed by a size analysis of amplified fragments. Peripheral blood from patients with nonlymphocyte-dependent disorders and matched by age and sex was assessed in the same conditions. Results in both groups were compared using nonparametric statistical tests. Results, Overall, a circulating dominant T-cell clone was found in 52% of patients compared with 16·9% in controls. More precisely, such a dominant clone was present in 43% and 37% of cutaneous and systemic lupus erythematosus, respectively, in 75% of multiple morphea, 75% of regional scleroderma and 60% of CREST syndrome patients. The percentages in all subsets of patients were significantly higher than in the control group. Conclusions, The presence of a dominant T-cell clone in peripheral blood is significantly more frequent in collagen vascular disorders than in controls, especially in patients with scleroderma, whatever the clinical subset, which suggests T-cell involvement in the immune response dysfunction in these diseases classically characterized by disturbances of B lymphocytes. The relevance of such a dominant clone regarding diagnosis, pathomechanisms, long-term outcome and visceral prognosis of these diseases as well as therapeutic decisions remains to be evaluated. [source]

1342: Communicating numerical results correctly

ACTA OPHTHALMOLOGICA, Issue 2010
T KIVELÄ
Purpose To highlight some pearls and pitfalls in reporting numerical data related to the eye with special reference to the instructions of the EVER Journal, Acta Ophthalmologica. Methods Personal experience of the author as a writer, reviewer and editorial board member is used to highlight common issues specific for reporting statistics. The rules and the reasoning behind them are explained using abundant real life examples. Results Statistics and mathematical analyses applied should be described in the methods section, but the software used need not be referenced unless it is specific for the test used. The following rules regarding reporting are highly recommended: 1. Report proportions if the number of subjects is smaller than 10; percentages in integers if the number of subjects is less than 100; if the number of subjects is larger, one decimal place can be given but is seldom necessary. 2. Report summary statistics of normally distributed variables as mean with standard deviation; other variables as medium with range. 3. Use parametric and nonparametric statistical tests accordingly. 4. Give exact p-values (e.g. p=0.034); if p-value is less than 0.001, report p<0.001. 5. Give 95% confidence intervals for main findings. 6. Mention the statistical test used with the p-value (e.g. p=0.015, paired t-test) if multiple methods are used. Conclusion Efficient reporting and analysis of data related to the eye is not difficult as long as one is aware of the basic rules. Putting them into action helps to ensure that the conclusions the readers draw from your study are proper. [source]