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PubMed2004

Nonparametric procedures for simultaneous identification of the minimum effective dose in each of several groups.

This paper considers the extension of the dose finding problem in a one-way layout setting to the case of several groups, in which the main goal is to identify the minimum effective dose (MED) of each group simultaneously. We propose two nonparametric procedures using the respective pairwise- and Helmert-type two-sample Mann-Whitney statistics, which are applied in a step-down testing scheme for identifying the MED simultaneously. The computation for the associated p-value of the identified MED vector is discussed. One numerical example is given to illustrate the proposed procedures.

Algorithms↗
PubMed2004

Relative connective tissue graft size affects root coverage treatment outcome in the envelope procedure.

BACKGROUND: This study investigated the correlation between the connective tissue graft size and the percentage of root coverage. METHODS: Fifteen patients with Miller Class I or II recession defects (one tooth/defect per patient) were treated using an envelope connective tissue graft procedure. Clinical parameters including gingival recession depth (RD), clinical attachment level (CAL), keratinized tissue width (KW), and the probing depth (PD) were measured. Visible denuded area (VDA) and graft tissue area (GTA) were indirectly measured in mm2 using computer software. Graft tissue thickness (GTT) and graft tissue width (GTW) were also measured. All clinical parameters and VDA were recorded at baseline and 3 and 6 months. The RD, CAL, KW, PD, and VDA were evaluated by Friedman test. The correlation between the percentage of root coverage (PRC) and factors related to graft size were determined by Spearman rank correlation and nonparametric regression analysis. RESULTS: The percent of root coverage at 3 and 6 months postoperatively was statistically significantly associated with the GTA:VDA ratio (P<0.01); it did not correlate with GTA, GTT, or RD, and was inconsistently correlated to GTW and VDA. In patients who had 100% root coverage, the GTA:VDA ratio ranged between 10.92:1 and 21.95:1; in patients with <100% root coverage, the ratio was between 4.54:1 and 11.06:1. CONCLUSION: The GTA:VDA ratio should be at least 11:1, which is a significant factor for optimal root coverage result in the envelope procedure.

Adult↗
PubMed1996

Dual site ambulatory pH monitoring: a probe across the lower esophageal sphincter does not induce gastroesophageal reflux.

BACKGROUND: Twenty-four-hour ambulatory pH studies have traditionally been performed with placement of the pH electrodes proximal to the lower esophageal sphincter (LES). More recently, simultaneous gastric and esophageal pH monitoring studies have been performed to allow the simultaneous assessment and correlation of esophageal and gastric pH. OBJECTIVES: The purpose of this study was to determine if pH probe placement across the LES increases esophageal acid exposure either in asymptomatic, healthy volunteers or in symptomatic patients with a documented history of erosive esophagitis. METHODS: Ten healthy volunteers (five female, five male; mean age 27 yr) and 13 patients with endoscopically confirmed erosive esophagitis (seven female, six male; mean age 35 yr) were randomly assigned, in cross-over fashion, into two protocols. The first protocol required placement of a dual antimony pH electrode catheter (2.1-mm outside diameter) across the LES with pH electrodes positioned 5 cm above and 10 cm below the manometrically identified LES. The second protocol required catheter placement 5 cm and 20 cm above the LES. Twenty-four-hour pH monitoring was performed on all subjects. Healthy volunteers were permitted an unrestricted diet and were studied in an out-patient setting. Symptomatic patients were assessed in an inpatient setting on a standardized diet with a refluxogenic dinner meal. RESULTS: The total number of reflux episodes, number of reflux episodes greater than 5 min, and the fraction of time that pH was less than 4 were evaluated over the total 24-h time period in the upright and supine positions. Nonparametric paired tests including a Wilcoxon signed rank test and a Robust analysis were used for statistical assessment. There was no significant increase in gastroesophageal reflux observed with placement of the pH probe across the LES either in the asymptomatic healthy volunteers or in patients with documented erosive esophagitis. Neither upright nor supine esophageal acid exposures were modified by catheter placement. CONCLUSIONS: Our study results indicate that placement of a 2.1-mm diameter pH probe across the LES does not induce reflux in asymptomatic healthy volunteers or in patients with GERD. Dual site ambulatory pH monitoring with trans-sphincteric pH catheter placement is a valid diagnostic technique that can be applied clinically when required.

Adult↗
PubMed2006

Parametric and nonparametric FDR estimation revisited.

Nonparametric and parametric approaches have been proposed to estimate false discovery rate under the independent hypothesis testing assumption. The parametric approach has been shown to have better performance than the nonparametric approaches. In this article, we study the nonparametric approaches and quantify the underlying relations between parametric and nonparametric approaches. Our study reveals the conservative nature of the nonparametric approaches, and establishes the connections between the empirical Bayes method and p-value-based nonparametric methods. Based on our results, we advocate using the parametric approach, or directly modeling the test statistics using the empirical Bayes method.

Bayes Theorem↗
PubMed2006

Checking linearity of non-parametric component in partially linear models with an application in systemic inflammatory response syndrome study.

Two tests are proposed for checking the linearity of nonparametric function in partially linear models. The first one is based on a Crámer-von Mises statistic. This test can detect the local alternative converging to the null at the parametric rate 1/square root n. A bootstrap resample technique is provided to calculate the critical values. The second one is constructed in a penalized spline framework along with linear mixed-effects (LME) modeling. This is an extension likelihood ratio test for testing zero variance of random effects in LME models. Simulation experiments are conducted to explore the numerical performance of two tests. It is observed that two tests have good level properties, and the first test has a substantially superior power property over the second test in a variety of cases. A real data set is analysed with the proposed tests.

Humans↗
PubMed2000

Regulation of quantal size by presynaptic mechanisms.

Quantal size is often modeled as invariant, although it is now well established that the number of transmitter molecules released per synaptic vesicle during exocytosis can be modulated in central and peripheral synapses. In this review, we suggest why presynaptically altered quantal size would be important at social synapses that provide extrasynaptic neurotransmitter. Current techniques used to measure quantal size are reviewed with particular attention to amperometry, the first approach to provide direct measurement of the number of molecules and kinetics of presynaptic quantal release, and to CNS dopamine neuronal terminals. The known interventions that alter quantal size at the presynaptic locus are reviewed and categorized as (1) alteration of transvesicular free energy gradients, (2) modulation of vesicle transmitter transporter activity, (3) modulation of fusion pore kinetics, (4) altered transmitter degranulation, and (5) changes in synaptic vesicle volume. Modulation of the number of molecules released per quantum underlies mechanisms of drug action of L-DOPA and the amphetamines, and seems likely to be involved in both normal synaptic modification and disease states. Statistical analysis for examining quantal size and data presentation is discussed. We include detailed information on performing nonparametric resampling statistical analysis, the Kolmogorov-Smirnov test for two populations, and random walk simulations using spreadsheet programs.

Animals↗
PubMed2002

Evaluation of compatibility between different types of adhesives and dual-cured resin cement.

PURPOSE: The objective of this in vitro study was to evaluate the bonding compatibility between different adhesives and a dual-cured resin cement, using a conventional tensile bond test. MATERIALS AND METHODS: The adhesives used were: Prime & Bond (PB) (Dentsply) (PB), Scotchbond Multi Purpose (SB) (3M), and the activator Self Cure (SC) (Dentsply). The dual-curing resin cement used was Enforce (EF) (Dentsply). Six groups with five specimens in each were tested: G1: EF/PB/EF (light cured); G2: EF/SB/EF (light cured); G3: EF/PB+SC/EF (light cured); G4: EF/PB+SC/EF (only chemically cured); G5: EF/EF (light cured); G6: EF/EF (only chemically cured). The resin cement was applied in two stainless steel molds with a cone-shaped perforation measuring 4 mm in diameter and 1 mm in thickness, and the adhesive was applied between them. Ten minutes after specimens were cured, the tensile strength was measured in a universal testing machine at a crosshead speed of 0.5 mm/min. RESULTS: The mean values (MPa) +/- SD obtained in each experimental group were: G1: 1.4 +/- 0.2; G2: 1.3 +/- 0.2; G3: 1.2 +/- 0.4; G4: 0.8 +/- 0.2; G5: 1.2 +/- 0.1; G6: 0.7 +/- 0.1. The results were statistically evaluated using nonparametric Kruskal-Wallis and Dunn tests (p < or = 0.05). Statistically significant differences among groups were found only between G1 and G4, and G1 and G6. CONCLUSION: There was no incompatibility among the different adhesives used with dual-cured resin cement. The lowest tensile bond strength values occurred in the absence of photoactivation.

Acetone↗
PubMed2004

Patterns of tooth crown size and shape variation in great apes and humans and species recognition in the hominid fossil record.

It has been suggested that patterns of craniodental variation in living hominids (Gorilla, Homo, Pan, and Pongo) may be useful for evaluating variation in fossil hominid assemblages. Using this approach, a fossil sample exhibiting a pattern of variation that deviates from one shared among living taxa would be regarded as taxonomically heterogeneous. Here we examine patterns of tooth crown size and shape variation in great apes and humans to determine 1) if these taxa share a pattern of dental variation, and 2) if such a pattern can reliably discriminate between samples that contain single species and those that contain multiple species. We use parametric and nonparametric correlation methods to establish the degree of pattern similarity among taxa, and randomization tests to assess their statistical significance. The results of this study show that extant hominids do not share a pattern of dental size variation, and thus these taxa cannot be used to generate expectations for patterns of size variation in fossil hominid species. The hominines (Gorilla, Homo, and Pan) do share a pattern of shape variation in the mandibular dentition; however, Pongo is distinct, and thus it is unclear which, if either, pattern should be expected in fossil hominids. Moreover, in this case, most combined-species samples exhibit patterns of shape variation that are similar to those for single hominine species samples. Thus, although a common pattern of shape variation is present in the mandibular dentition, it is not useful for recognizing taxonomically mixed paleontological samples.

Animals↗
PubMed1997

Bacterial penetration through temporary restorative materials in root-canal-treated teeth in vitro.

Seventy extracted single-rooted mandibular premolars were used in this study to determine the length of time needed for bacteria present in natural human saliva to penetrate through three commonly used temporary restorative materials and through the entire root canal system obturated with the lateral condensation technique. Five intact teeth with no decay were used in the negative control group and five teeth with extensive decay in communication with the canal, in the positive control group. The 60 teeth used in the experimental group were divided into three groups. In Group 1, the access cavities of 20 teeth were temporarily restored with gutta percha, in Group 2 with IRM and in Group 3 with Cavit-G. All 70 teeth were mounted individually where the crown was placed in contact with human saliva. All five teeth in the positive control group caused broth turbidity within 24 h. In contrast, broth in the negative control group remained clear throughout the entire experimental period. In the experimental group, the average time for broth contamination of access cavities closed with gutta percha, IRM and Cavit-G was 7.85, 12.95 and 9.80 days, respectively. The Kruskal-Wallis nonparametric test showed significant differences among the groups, while the multiple comparison test showed that the IRM group was statistically better than the gutta percha group when the average lengths of time for contamination were compared (P < 0.05).

Dental Cements↗
PubMedDate not supplied

The influence of post length and crown ferrule length on the resistance to cyclic loading of bovine teeth with prefabricated titanium posts.

PURPOSE: The purpose of this in vitro study was to evaluate the influence of post and ferrule length on the resistance to cyclic (fatigue) loading of teeth with prefabricated titanium posts (ParaPost) and crowns. MATERIALS AND METHODS: Ninety bovine teeth with similar dimensions were mounted in acrylic blocks with artificial silicone periodontal ligaments. Combinations of post lengths of 5 mm, 7.5 mm, and 10 mm, and ferrule lengths (i.e., the vertical dentinal overlap of the crown) of 0 mm, 1.25 mm, and 2.5 mm made up 9 different groups consisting of 10 teeth each. The posts were cemented with zinc phosphate cement. Composite-resin cores were made and crowns were cemented. Each test specimen underwent cyclic loading of 400 N with a frequency of 1 load per second at an angulation of 45 degrees to the long axis of the tooth. RESULTS: All but 2 specimens failed with a root fracture; in the remaining 2 specimens the core lost retention. A large variation in the results between the various groups was observed. A nonparametric 2-way analysis for groups with a natural order revealed that the fracture resistance to cyclic loading increased statistically significantly with increasing ferrule length (P < 0.01), whereas increasing post length did not increase fracture resistance (P = 0.44). CONCLUSION: Ferrule length was more important than post length in increasing fracture resistance to cyclic loading of crowned teeth.

Animals↗
PubMed1997

An age-adjusted trend test for the tumor incidence rate for multiple-sacrifice experiments.

The nonparametric age-adjusted trend test for the tumor incidence rate proposed by Malani and Lu (1993, Communications in Statistics--Theory and Methods 22, 1557-1584) is modified in two ways to improve the size of the test. First, the tumor incidence rate is constrained to be nonnegative, and second, a conditional variance is used in place of the asymptotic variance based on the delta method. A Monte Carlo simulation study demonstrates the improvement in size of test. The proposed test can be viewed also as a modification of the two-group test of Dewanji and Kalbfleisch (1986, Biometrics 42, 325-341), although their maximum likelihood routine is based on a different formulation of the problem.

Age Factors↗
PubMed2005

Computer-aided lung nodule detection in CT: results of large-scale observer test.

RATIONALE AND OBJECTIVES: The objective is to study the incremental effects of using a computer-aided lung nodule detection (CAD) system on the performance of a large pool of observers. MATERIALS AND METHODS: A set of eight thin-section computed tomographic data sets with limited longitudinal coverage, containing a total of 22 lung nodules, was analyzed by using the automated nodule detection system. When applied to all eight cases, the CAD system alone achieved a detection rate of 86.4%, with 2.64 false-positive results per case. This study included 202 observers at a national radiology meeting: 39 thoracic radiologists, 95 non-thoracic radiologists, and 68 non-radiologists. Each participant read from one to eight cases in random order, first without and then with CAD system output available. Observer performance in nodule detection was measured before and after CAD was made available. Differences in performance of groups of observers before and after CAD were tabulated by mean, median, and SD in detection rate and number of false-positive results and tested by using nonparametric methods. RESULTS: In an analysis involving only the first randomly selected case read by all 202 participants, there were statistically significant increases in nodule detection rates and numbers of false-positive results for all types of observers. There was a significant difference in detection rates between radiologists and non-radiologists before CAD, but after CAD, there was no significant difference in detection rates between these observer types. In a second analysis involving 13 participants who read all eight cases, mean detection rates were 64.0% before CAD and 81.9% after CAD. Mean numbers of false-positive results were 0.144 per case before CAD and 0.173 after CAD. CONCLUSION: In a large observer study, use of a CAD system for nodule detection resulted in an incremental increase in detection rate, but also led to an increase in number of false-positive results. Also, CAD appears to be an equalizer of detection rates between observers of different levels of experience.

Clinical Competence↗
PubMed2006

A nonparametric approach for detection of bursts in spike trains.

In spike-train data, bursts are considered as a unit of neural information and are of potential interest in studies of responses to any sensory stimulus. Consequently, burst detection appears to be a critical problem for which the Poisson-surprise (PS) method has been widely used for 20 years. However, this method has faced some recurrent criticism about the underlying assumptions regarding the interspike interval (ISI) distributions. In this paper, we avoid such assumptions by using a nonparametric approach for burst detection based on the ranks of ISI in the entire spike train. Similar to the PS statistic, a "Rank surprise" (RS) statistic is extracted. A new algorithm performing an exhaustive search of bursts in the spike trains is also presented. Compared to the performances of the PS method on realizations of gamma renewal processes and spike trains recorded in cat auditory cortex, we show that the RS method is very robust for any type of ISI distribution and is based on an elementary formalization of the definition of a burst. It presents an alternative to the PS method for non-Poisson spike trains and is simple to implement.

Action Potentials↗
PubMed2000

Nonparametric rank-based methods for group sequential monitoring of paired censored survival data.

This research gives methods for nonparametric sequential monitoring of paired censored survival data in the two-sample problem using paired weighted log-rank statistics with adjustments for dependence in survival and censoring outcomes. The joint asymptotic closed-form distribution of these sequentially monitored statistics has a dependent increments structure. Simulations validating operating characteristics of the proposed methods highlight power and size consequences of ignoring even mildly correlated data. A motivating example is presented via the Early Treatment Diabetic Retinopathy Study.

Biometry↗