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PubMed2001

Carryover bias in visual assessment.

Carryover of stimuli in sequential judgments was studied for a visual assessment task involving estimation of the percentage cover of black circles on a white image. Seven image types with different levels of cover density were arranged in a sequentially balanced design in which each image type was preceded the same number of times by all image types. In the absence of carryover, when images were preceded by images with the same cover density, the response scores were well fitted by a power function of percentage cover with a mean exponent of 0.73 over subjects. Carryover took the form of an assimilation, so that the cover estimate for a target image was generally higher when preceded by an image with higher cover, and lower when preceded by an image with lower cover. However, the magnitude of the carryover effect showed little evidence of increasing with difference in cover between successive images. Nonparametric and parametric methods for testing for carryover are presented. The need for development of psychological models to explain the proposed statistical models is discussed.

Adolescent↗
PubMed2005

Nonparametric confidence intervals for the one- and two-sample problems.

Confidence intervals for the mean of one sample and the difference in means of two independent samples based on the ordinary-t statistic suffer deficiencies when samples come from skewed families. In this article we evaluate several existing techniques and propose new methods to improve coverage accuracy. The methods examined include the ordinary-t, the bootstrap-t, the biased-corrected acceleration and three new intervals based on transformation of the t-statistic. Our study shows that our new transformation intervals and the bootstrap-t intervals give best coverage accuracy for a variety of skewed distributions, and that our new transformation intervals have shorter interval lengths.

Computer Simulation↗
PubMed2005

Delaire's cheilorhinoplasty: unilateral cleft aesthetic outcome scored according to the EUROCLEFT guidelines.

OBJECTIVE: The aim of our study is to evaluate, in accordance with EUROCLEFT guidelines, the aesthetics of nasolabial area in a sample of complete unilateral cleft of lip and palate patients (UCLP), after surgical correction with Delaire' technique. METHODS: Twenty-two UCLP patients (16 males and 6 females, 9 right and 13 left side clefts) were enrolled in this retrospective study. Patients were operated at 7 (mean value) months of age by a single surgeon. Frontal and sub-mental photos for each baby were recorded at 8.5 (mean value) years of age, and evaluated twice, by three independent maxillofacial surgeons. A five-point scale (EUROCLEFT guidelines) was used. Nonparametric analysis (Kruskal-Wallis test) was applied to detect differences in medians obtained in studied groups. RESULTS: Kruskal-Wallis test showed no statistical significant differences among evaluations of three surgeons and between the first and the second evaluation of the same surgeon. The global appearance of the upper lip and nose was scored with a mean value of 2 (i.e. good). The sample was then divided into two subgroups, according with patient' age; the aesthetics and the symmetry of the nose resulted better in elder patients (i.e. subgroup A, mean period of observation=10.2 years), whereas upper lip achieved better results in younger patients (i.e. subgroup B, mean period of observation=4.9 years). CONCLUSIONS: EUROCLEFT guidelines are a useful method to evaluate--aesthetically and over time--cleft lip and palate patients, treated with a single surgical procedure. We hypothesize that Delaire technique could progressively improve aesthetics and symmetry of the nose, throughout the growth of the patient.

Child↗
PubMed2000

Image analysis of mesothelioma. I. differentiation of mesothelioma from adenocarcinoma of the lung.

OBJECTIVE: To explore the usefulness of nuclear micromorphometric analysis for the differentiation between epithelial mesothelioma and metastatic adenocarcinoma in the chest wall. STUDY DESIGN: High-resolution images of 2,100 nuclei from 27 cases of epithelial mesothelioma and 15 cases of adenocarcinoma of the lung were recorded. Stepwise discriminant analysis and a nonparametric classifier were applied to derive estimates for a case diagnosis correct classification rate. RESULTS: Nuclei from epithelial mesothelioma and adenocarcinoma of the lung showed statistically significantly different properties, but there was a region of overlap in feature space such that approximately 15-20% of cases could not be correctly classified. The lesion signatures derived from the mesothelioma cases with discriminant function scores that might result in case misclassification and the cases of adenocarcinoma of the lung spanned a similar range of degree of nuclear abnormality. However, the distribution of nuclear abnormality values for the mesothelioma cases has a mode at 0.87 SD from normal, whereas the distribution seen in lung adenocarcinoma cases had a mode at about 3.7 SD. CONCLUSION: Cases of epithelial mesothelioma and adenocarcinoma of the lung have nuclei with a wide range of deviation from normal in the spatial and statistical distribution of their nuclear chromatin. For approximately 80% of cases, correct case classification can be provided by nuclear micromorphometric analysis. Cases of epithelial mesothelioma with highly abnormal nuclei overlap in feature space with nuclei from adenocarcinoma of the lung. However, it is possible that characterization by a lesion signature may allow correct assignment for those cases.

Adenocarcinoma↗
PubMedDate not supplied

Approximate minimum bias multichannel spectral estimation for heart rate variability.

Spectral decomposition of variations in heart rate permits noninvasive measurement of autonomic nervous activity in humans and animals. Autonomic metrics based on spectral analysis are useful in monitoring clinical conditions such as diabetic neuropathy and reinnervation in heart transplant patients. A persistent problem in deriving such autonomic measures is the prerequisite of an accurate and unbiased power spectrum of heart rate variability (HRV). Numerous parametric and nonparametric power spectrum estimators have been introduced, each with its own advantages and drawbacks. Estimator bias has received little attention, despite the fact that at least one common HRV spectrum estimator, the autoregressive method, is known to exhibit bias even in idealized circumstances. We introduce an approximately minimum bias, nonparametric, multichannel spectrum estimation procedure for HRV and contemporaneous signals. The procedure, which is designed specifically for irregular sampling, does not require data segmentation and provides statistically consistent, low variance multichannel spectrum estimates. Estimator performance on simulated and clinical data is presented and compared with results from autoregressive models and Welch periodograms with and without compensation for irregular sampling. Results indicate that the proposed method exhibits advantages over conventional HRV spectrum estimators. Relative computational complexity of the proposed method is also considered.

Adult↗
PubMed2003

How to model a complex trait. 1. General considerations and suggestions.

Usually, when complex traits are at issue, not only are the loci of the responsible genes a priori unknown; the same also holds for the mode of inheritance of the trait, and sometimes even for the phenotype definition. The term mode of inheritance relates to both the genetic mechanism, i.e., the number of loci implicated in the etiology of the disease, and the genotype-phenotype relation, which describes the influence of these loci on the trait. Having an idea of the genetic model can crucially facilitate the mapping process. This holds especially in the context of linkage analysis, where an appropriate parametric model or a suitable nonparametric allele sharing statistic may accordingly be selected. Here, we review the difficulties with parametric and nonparametric linkage analysis when applied to multifactorial diseases. We address the question why it is necessary to adequately model a genetically complex trait in a linkage study, and elucidate the steps to do so. Furthermore, we discuss the value of including unaffected individuals into the analysis, as well as of looking at larger pedigrees, both with parametric and nonparametric methods. Our considerations and suggestions aim at guiding researchers to genotyping individuals at a trait locus as accurately as possible.

Chromosome Mapping↗
PubMedDate not supplied

Cariogenic oral flora and its relation to dental caries.

Many attempts have been made to establish the risk profile of dental caries; however, no diagnostic procedures are yet available to reliably predict such risk particularly among the pediatric and adolescent population. Age of subject, a history of caries affecting the primary dentition, the prevalence of Streptococcus mutans, pH values, salivary flow, and the frequency and amount of sugar consumption have been the factors most studied. A cross-sectional study is made of schoolchildren in the 12-13-year age-range to evaluate the relationship between dental caries and CFU/ml of S. mutans and Lactobacillus, salivary buffer capacity, and salivary flow. Likewise, an evaluation is made of the predictive value of the variables, bacterial count and salivary pH with respect to caries. A total of 167 children were subjected to oral examination to establish the DMFT and DMFS indices, followed by the collection of saliva for quantitating S. mutans, Lactobacillus, pH and salivary flow, by the Dentocult (SM)(LB) and Dentobuff systems (Vivadent). The data obtained were subjected to descriptive analysis, comparisons among variables were made by nonparametric testing with a confidence level of 95 percent. Test predictive value was studied in terms of sensitivity, specificity, positive and negative predictive values, and probability ratio. Statistically significant (p < 0.001) correlations were observed between the caries indices and bacterial counts. No significant association was recorded with the rest of the variables studied. Bacterial counts as well as salivary buffer capacities exhibited greater negative than positive predictive values, i.e., they were more effective in identifying healthy individuals than patients who required treatment.

Adolescent↗
PubMed2004

[The influence of carcinogenesis in the oral cavity on the level of zinc, copper and iron in serum].

Samples of blood serum originating from the patients with squamous cell carcinoma of various parts of the oral cavity (carcinoma planoepitheliale spinocellulare: mucosae buccae, fundi oris, linguae, palati molli) were analyzed for presence of some microelements (zinc, copper and iron) using the AAS method. The findings were compared to amounts of these elements in serum of healthy persons (control samples). Significant differences among groups (with cancer and control) were qualified using nonparametric U-Mann Whitney test. The mean contents of all the analyzed microelements in serum of persons with cancer were higher as compared with controls but statistically significant differences were only in case of copper and iron.

Carcinogens↗
PubMed2005

Single-session alcohol-retention sclerotherapy for simple renal cysts: comparison of 2- and 4-hr retention techniques.

OBJECTIVE: The objectives of our study were to evaluate the feasibility of ethanol sclerotherapy in treating simple renal cysts with prolonged ethanol retention and to compare the therapeutic results of 2- and 4-hr retention techniques. MATERIALS AND METHODS: We retrospectively reviewed 36 renal cysts in 33 patients treated by ethanol sclerotherapy with a single-session single-injection technique during the past 6 years. After complete aspiration of the cystic fluid, 95% ethanol was injected into the cyst and was retained for 4 hr in 14 cysts (group 1) and for 2 hr in 22 cysts (group 2). The average maximal diameter and aspirated volume of the cysts were 8.3 cm and 223 mL in group 1 patients and 7.9 cm and 167 mL in group 2, respectively. The ablated cysts were followed up regularly by sonography, CT, or both at 3- to 6-month intervals for at least 1 year. The nonparametric Mann-Whitney U test was used to compare differences in characteristics, treatment results, and laboratory data of the subjects in the two groups. The level of statistical significance was set at a p value of less than 0.05. RESULTS: Technically, all the patients tolerated the procedures. One patient had gross hematuria 10 days after the procedure. She underwent surgical deroofing treatment and was excluded in the later statistical analysis. After sclerotherapy, 14 cysts disappeared completely and 16 cysts showed marked regression with residual maximal diameter of less than 3 cm. The overall volume reduction rate was 97.6% in all 35 cysts. The mean residual longest diameters and average volume reduction rates of the treated cysts were 1.9 cm and 97.9% in group 1 patients and 1.1 cm and 97.3% in group 2 patients, respectively, which showed no statistical significance of volume reduction rate with a p value 0.149. CONCLUSION: The single-session prolonged ethanol-retention technique is safe and efficacious for the treatment of renal cysts. There is no statistical difference in therapeutic efficacy between 2- and 4-hr ethanol-retention techniques.

Adult↗
PubMed2007

Nonparametric estimation of the mean function of a stochastic process with missing observations.

In an attempt to identify similarities between methods for estimating a mean function with different types of response or observation processes, we explore a general theoretical framework for nonparametric estimation of the mean function of a response process subject to incomplete observations. Special cases of the response process include quantitative responses and discrete state processes such as survival processes, counting processes and alternating binary processes. The incomplete data are assumed to arise from a general response-independent observation process, which includes right-censoring, interval censoring, periodic observation, and mixtures of these as special cases. We explore two criteria for defining nonparametric estimators, one based on the sample mean of available data and the other inspired by the construction of Kaplan-Meier (or product-limit) estimator [J. Am. Statist. Assoc. 53 (1958) 457] for right-censored survival data. We show that under regularity conditions the estimated mean functions resulting from both criteria are consistent and converge weakly to Gaussian processes, and provide consistent estimators of their covariance functions. We then evaluate these general criteria for specific responses and observation processes, and show how they lead to familiar estimators for some response and observation processes and new estimators for others. We illustrate the latter with data from an recently completed AIDS clinical trial.

Acquired Immunodeficiency Syndrome↗
PubMed2005

One-sided nonparametric tests for ordinal data.

Baumgartner, Weiss, and Schindler (1998) introduced a novel non-parametric test for the two-sample comparison that is superior to commonly used tests such as the Wilcoxon rank-sum test. A modification of the novel test statistic can be used for one-sided comparisons based on ordinal data. Such comparisons frequently occur in psychological research, and the Wilcoxon test is often recommended for their analysis. Here, the two tests were compared in a simulation study. According to this study the tests have a similar type I error rate, but the modified Baumgartner-Weiss-Schindler test is more powerful than the Wilcoxon test.

Data Interpretation, Statistical↗
PubMed2004

[Allergen specific-IgG4 in circulating immune complexes in patients with inhalant allergy undergoing specific immunotherapy].

The mechanism of action of specific immunotherapy (SIT) is still not definitely clear. The problem of the presence of allergen specific-IgG4 in circulating immune complexes (CIC) of patients with inhalant allergy is being discussed. The aim of the study was to determine the allergen specific-IgG4 serum levels and concentration in CIC in patients with inhalant allergy who underwent specific immunotherapy with relevance to its clinical benefits. The trial was carried out on 57 patients with seasonal allergic rhinitis (SAR) and 55 with perennial allergic rhinitis (PAR). Each of them underwent 3-year specific immunotherapy with Allergovit (Nexter-Allergopharma) or Novo Helisen Depot (Nexter-Allergopharma). 56 patients with pharmacologically treated allergic rhinitis served as a control group. Serum levels of allergen specific-IgG4 (as-IgG4), IgE, as-IgE and as-IgG4 concentration in CIC were measured in each patient and correlated with the clinical score of the disease activity. Nonparametric tests (the U Mann-Whitney test, Kruskall-Wallis test and Spearman's correlation rang test) were used. Serum levels of as-IgG4 and bound in CIC were statistically higher in the SIT group than in the control group and differed significantly between SAR and PAR groups. Immunotherapy caused significantly higher concentrations of as-IgG4 in CIC in PAR group than in SAR patients. No significant associations were found between studied immunological indices and clinical effects of SIT. Specific immunotherapy of allergic rhinitis is connected with the increase of as-IgG4 serum level and its concentration in circulating immune complexes.

Adult↗
PubMed2004

[A review of nonparametric test].

For some data which have skewness distribution or unknown distribution, it is impossible to apply parametric test. Nonparametric test will be a good choice for this kind of data in testing the distribution of the population. The nonparametric test is widely used in clinical research by its goodness of stability and adaptiveness. However, the effectiveness is cutting down by losing some essential information. So, parametric test will be recommended when the data meet the requirements. This paper introduces the basic concepts and methods of nonparametric test for the physicians to understand this important tool.

Humans↗