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PubMed2003

Differences in mite fauna between the continental and Mediterranean climates of Croatia: microscopy and Dustscreen test findings.

BACKGROUND: The aim of this study was to evaluate the difference between the mite fauna in the inland and coastal Croatia. METHODS: Ninety-nine floor house dust samples were collected: 28 from the coastal area, 31 from the inland rural and 40 from the inland urban area. Data on basic household characteristics were collected for 81 of 99 households. The mites were separated from the dust using the floatation method and then microscopically identified. The levels of Dermatophagoides pteronyssinus (Der p) 1, Dermatophagoides farinae (Der f) 1 and Der 2 were measured using the Dustscreen test. Ordinal descriptive statistics and nonparametric tests were used for data analysis, assuming statistical significance at P < 0.05. RESULTS: More than 70% of mites identified in all areas were pyroglyphids. Nonpyroglyphid mites accounted for 20-25% of all identified mites in the coastal areas (Blomia, Lepidoglyphus and Glycyphagus) and with 15% in the inland areas (Lepidoglyphus and Acarus). The highest Der p 1 median levels were found in the coastal area, with significantly lower levels in the inland rural and inland urban areas (4.5; 2; 0.85 microg/g of dust; P = 0.0001). The highest Der f 1 median levels were found in the inland urban area, with significantly lower levels in the inland rural and coastal areas (0.88; 0.75; 0 microg/g of dust; P = 0.0013). The levels of Der f 1 were significantly higher in samples taken from households with central heating than from those with traditional heating (1; 0.25 microg/g of dust; P < 0.01). CONCLUSIONS: Separate diagnostic dust mite lists for the coastal and inland areas because of climatic and dwelling differences required to be implemented. Compared with traditional heating, central heating significantly increases the risk of exposure to Der f 1 levels >2 microg/g of dust (odds ratio, 7.35; 95% confidence interval, 1.43-37.87; P = 0.01).

Animals↗

PubMed2002

Effectiveness of manual and rotary instrumentation techniques for cleaning flattened root canals.

The cleaning capacity of manual and rotary instrumentation techniques in mesial-distal flattened canals was studied by morphometric analysis. Twenty human mandibular incisors were divided into two groups of 10 teeth each: group 1, crown-down technique with rotary instrumentation using ProFile .04; group 2, crown-down technique with manual instrumentation using K-files. The teeth were evaluated with an optic microscope that was coupled to a computer to determine the percentage of root canal area with debris. The nonparametric Mann-Whitney U test showed a statistically significant difference at the level of 1% between the techniques. The manual technique was more efficient in cleaning mesial-distal flattened root canals than the rotary technique, although neither completely cleaned the root canal.

Dental Instruments↗

PubMed2003

Evaluation of marginal microleakage in class II cavities: effect of microhybrid, flowable, and compactable resins.

OBJECTIVE: The goal of the present study was to evaluate the microleakage on the cementum/dentin and enamel surfaces in Class II restorations, using different kinds of resin composite (microhybrid, flowable, and compactable). METHOD AND MATERIALS: Forty human caries-free molars were extracted and selected. Eighty Class II standardized cavities were made in the cervical wall at the cementoenamel junction (CEJ) and at the mesial and distal surfaces. The teeth were divided into four groups: G1--adhesive system + microhybrid resin composite Z100; G2--adhesive system + compactable resin composite Prodigy Condensable; G3--adhesive system + flowable resin composite Revolution + Z100 resin composite; G4--adhesive system + Revolution fluid resin + compactable resin composite Prodigy Condensable. The adhesive system used in this study was Scotchbond Multi-Purpose Plus. The specimens were thermocycled in baths of 5 degrees C and 55 degrees C for 1,000 cycles and immersed in 50% silver nitrate solution. The specimens then were sectioned and evaluated on degree of dye penetration. RESULTS: The results were evaluated using the nonparametric Kruskall-Wallis test, which showed a statistically significant difference between groups G1 and G4, G2 and G4, and G3 and G4. CONCLUSIONS: None of the materials was able to eliminate the marginal microleakage at the cervical wall; the application of a low-viscosity resin composite combined with a compactable resin composite significantly decreased the microleakage.

Composite Resins↗

PubMed1997

Nonparametric simulation based linkage statistics for general pedigrees.

A common strategy for testing for linkage without posing a disease model is to test for increased marker similarity among the affected pedigree members. We developed a simulation based statistic, SimIBD, which measures marker similarity in terms of identity-by-descent (IBD) when it can be determined whether or not the alleles are IBD, and in terms of the probability of the alleles being IBD when it cannot be determined. The SimIBD statistic is not only more powerful than its precursor, the affected-pedigree-member (APM) method, but it is also less sensitive to the misspecification of marker allele frequencies.

Alleles↗

PubMed1999

Detection of bone invasion by gingival carcinoma of the mandible: a comparison of intraoral and panoramic radiography and computed tomography.

OBJECTIVE: To assess the diagnostic accuracy of panoramic radiography (PR), panoramic radiography combined with intraoral radiography (PR+IR), and CT in detecting the supero-inferior extent of tumor invasion of the mandible by gingival carcinoma. METHOD: PR, PR+IR, and CT images of the mandible in 37 patients with gingival carcinoma were evaluated by five oral radiologists for the supero-inferior extent of bone invasion using ROC analysis. The mean ROC curve area (Az) of each observer for the different imaging modalities was analysed by nonparametric two-way ANOVA. P<0.05 was considered statistically significant. RESULTS: The mean Az for the detection of bone invasion were 0.88+/-0.03 for PR, 0.77+/-0.12 for PR+IR, and 0.87+/-0.03 for CT (P=0.0907). The mean Az for the detection of bone invasion beyond the alveolus was 0.89+/-0.07 for PR, 0.85+/-0.08 for PR+IR, and 0.83+/-0.06 for CT (P=0.5438). The mean Az for the detection of bone invasion beneath the mandibular canal were 0.94+/-0.04 for PR, 0.94+/-0.02 for PR+IR, and 0.91+/-0. 04 for CT (P=0.2466). No statistically significant differences were observed in Az between PR, PR+IR, and CT. CONCLUSION: We consider that PR+IR should be adopted as the initial imaging modality to determine the extent of supero-inferior invasion of the mandible in gingival carcinoma.

Analysis of Variance↗

PubMed1997

Genetic heterogeneity in familial acute myelogenous leukemia: evidence for a second locus at chromosome 16q21-23.2.

The identification of genes responsible for the rare cases of familial leukemia may afford insight into the mechanism underlying the more common sporadic occurrences. Here we test a single family with 11 relevant meioses transmitting autosomal dominant acute myelogenous leukemia (AML) and myelodysplasia for linkage to three potential candidate loci. In a different family with inherited AML, linkage to chromosome 21q22.1-22.2 was recently reported; we exclude linkage to 21q22.1-22.2, demonstrating that familial AML is a heterogeneous disease. After reviewing familial leukemia and observing anticipation in the form of a declining age of onset with each generation, we had proposed 9p21-22 and 16q22 as additional candidate loci. Whereas linkage to 9p21-22 can be excluded, the finding of a maximum two-point LOD score of 2.82 with the microsatellite marker D16S522 at a recombination fraction theta = 0 provides evidence supporting linkage to 16q22. Haplotype analysis reveals a 23.5-cM (17.9-Mb) commonly inherited region among all affected family members extending from D16S451 to D16S289. In order to extract maximum linkage information with missing individuals, incomplete informativeness with individual markers in this interval, and possible deviance from strict autosomal dominant inheritance, we performed nonparametric linkage analysis (NPL) and found a maximum NPL statistic corresponding to a P-value of .00098, close to the maximum conditional probability of linkage expected for a pedigree with this structure. Mutational analysis in this region specifically excludes expansion of the AT-rich minisatellite repeat FRA16B fragile site and the CAG trinucleotide repeat in the E2F-4 transcription factor. The "repeat expansion detection" method, capable of detecting dynamic mutation associated with anticipation, more generally excludes large CAG repeat expansion as a cause of leukemia in this family.

Chromosome Mapping↗

PubMed2003

The effect of concurvity in generalized additive models linking mortality to ambient particulate matter.

In recent years, a number of studies have applied generalized additive models to time series data to estimate associations between exposure to air pollution and cardiorespiratory morbidity and mortality. If concurvity, the nonparametric analogue of multicollinearity, is present in the data, statistical software such as S-plus can seriously underestimate the variance of fitted model parameters, leading to significance tests with inflated type 1 error. This paper uses computer simulation and analyses of actual epidemiologic data to explore this underestimation of standard errors. We provide a method for assessing concurvity in data and an alternate class of models that is unaffected by concurvity. We argue that some degree of concurvity is likely to be present in all epidemiologic time series datasets and we explore through the use of meta-analysis the possible impact of concurvity on the existing body of work relating ambient levels of sulfate particles to mortality.

Air Pollutants↗

PubMed1994

Nonparametric scaling: a descriptive index.

A descriptive index (CI) based on the U statistic is presented. The CI permits to quantify the differences between experimental samples taking into account both the location and variability features of the data without any distributional assumption. This index can be useful to build activity scales for series of compounds.

Drug Evaluation↗

PubMed2000

Characterising life-span variability in a population using the life-table-based Lorenz-curve analysis.

BACKGROUND: 'Life expectancy' (LE) is a health-status indicator in widespread use. However, LE is an index of central location, but not of dispersion. It cannot describe inter-individual variation in the life-span. This author proposes using the Gini coefficient, a summary index of the Lorenz curve, for characterising life-span variability. Like the LE, the proposed index is also based on a lifetable. METHOD: The method is a nonparametric approach that does not make specific assumptions about mortality rates. RESULTS: The author uses vital statistics from Taiwan as a demonstration and finds that the method provides information crucial to the understanding of the epidemiologic transitions of the past 20 years (Gini decreases from 0.1320 to 0.1130). It also quantifies the impacts of elimination of some selected causes of death in Taiwan. CONCLUSIONS: It is recommended that Gini be routinely compiled in official vital statistics, along with the LE.

Adolescent↗

PubMed2001

Should we always choose a nonparametric test when comparing two apparently nonnormal distributions?

When clinical data are subjected to statistical analysis, a common question is how to choose an appropriate significance test. Comparing two independent groups with observations measured on a continuous scale, the question is typically whether to choose the two-sample-t test or the Wilcoxon-Mann-Whitney test (WMW test). Similar results are often obtained, but which conclusion can be drawn if significance tests give highly different P-values? The t test is optimal for normally distributed observations with common variance and robust to deviations from normality if sample sizes are not very small. The WMW test makes no distributional assumptions, but depends heavily on equal shape and variance of the two distributions (homoscedasticity). We have compared the properties of the traditional two-sample t test, a modified t test allowing unequal variance, and the WMW test by stochastic simulation. All show acceptable behaviour when the two distributions have similar variance. When variances differ, the modified t test is superior to the other two.

Analysis of Variance↗

PubMedDate not supplied

[The statistical evaluation of the reliability of learning curve differences].

A nonparametric method of statistical analysis of two related binary sequences of "1" and "0" is presented. This technique enables comparison between the dynamics of probability of appearance of 1" in the two sequences. This test can be applied to the problem of statistical comparison between the dynamics of learning of a "stimulus-reaction" type when the appearance of reaction to the stimulus is labeled as "1" and its absence as "0". The graphical interpretation is given and IBM-PC/AT program is characterized which realizes the advanced method.

Animals↗

PubMed2004

Effects of various irrigation solutions on microleakage of Class V composite restorations.

STATEMENT OF THE PROBLEM: Irrigation solutions used in the preparation of composite restorations have been reported to contain potential contaminants that may interfere with, and compromise, composite bonding. PURPOSE: The purpose of this in vitro study was to evaluate microleakage of Class V composite restorations after irrigation of acid conditioner with various solutions. MATERIAL AND MENTODS: Standardized Class V preparations (5 mm wide, 4 mm high and 2 mm deep) were made at the cemento-enamel junction on available buccal, lingual, mesial, and distal surfaces of extracted human posterior teeth. The prepared teeth, separated into 7 groups (n=10), were etched for 10 seconds with a 37% phosphoric acid gel. Each group was irrigated with 1 of the following solutions: (1) tap water, (2) sterile water, (3) sodium chloride solution, (4) filtered water, (5) chlorhexidine, (6) sodium hypochlorite, and (7) distilled water. Each preparation was treated with a bonding agent (Opti-Bond Solo) and then restored with a hybrid composite (Herculite XRV). The restorations were polished with Soflex polishing disks and then thermal cycled for 1000 cycles between 5 degrees C and 55 degrees C with a 20-second dwell time. Assessment of microleakage was performed by application of a dye penetrant, sectioning of the teeth, and examination at original magnification x 20. The nonparametric Kruskal-Wallis test (alpha=.05) was used for statistical analysis. RESULTS: Microleakage ranging from 10% to 30% was observed in all groups tested. Tap water exhibited the highest incidence of leakage, sterile water the least, with the other irrigation solutions leading to intermediate leakage. However, there was no significant difference in microleakage resulting from any of the irrigation solutions tested. CONCLUSION: The effect of irrigation solutions used in this in vitro study was not significant.

Acid Etching, Dental↗

PubMed2003

Influence of operator experience on canal preparation time when using the rotary Ni-Ti ProFile system in simulated curved canals.

AIM: The aim of this study was to determine the influence of operator experience on the time needed for canal preparation when using a rotary nickel-titanium (Ni-Ti) system. METHOD: A total of 100 simulated curved canals in resin blocks were used. Four operators prepared a total of 25 canals each. The operators included practitioners with prior experience of the preparation technique, and practitioners with no experience. The working length for each instrument was precisely predetermined. All canals were instrumented with rotary Ni-Ti ProFile Variable Taper Series 29 engine-driven instruments using a high-torque handpiece (Maillefer, Ballaigues, Switzerland). The time taken to prepare each canal was recorded. Significant differences between the operators were analysed using the Student's t-test and the Kruskall-Wallis and Dunn nonparametric tests. RESULTS: Comparison of canal preparation times demonstrated a statistically significant difference between the four operators (P < 0.001). In the inexperienced group, a significant linear regression between canal number and preparation time occurred. CONCLUSION: Time required for canal preparation was inversely related to operator experience.

Analysis of Variance↗

PubMed2006

Surveillance of individual level disease maps.

Methods for the production of individual (address) level disease maps are often retrospective; they estimate a map of the average relative risk of disease over a study period. However, recently, epidemiologists have started to look at weekly or monthly reports of disease and assess them for any change in the distribution of relative risk. For example, in the United States of America, the Centre for Disease Control and Prevention now routinely collects information on over 50 notifiable diseases every week. In this paper we present a method for the detection of a sudden change in the geographical distribution of the disease in a prospective study. The method is based on an estimate of the directional derivative of the conditional probability of a case, given either a case or control has occurred. It is based on standard kernel approaches to nonparametric regression and it is readily applied in any standard statistical software package. Two simulated examples of sudden clustering around a fixed point are provided.

Humans↗

PubMed1997

Semiparametric regression analysis for recurrent event interval counts.

This paper deals with analysis of data from longitudinal studies where the rate of a recurrent event characterizing morbidity is the primary criterion for treatment evaluation. We consider clinical trials which require patients to visit their clinical center at successive scheduled times as part of follow-up. At each visit, the patient reports the number of events that occurred since the previous visit, or an examination reveals the number of accumulated events, such as skin cancers. The exact occurrence times of the events are unavailable and the actual patient visit times typically vary randomly about the scheduled follow-up times. Each patient's record thus consists of a sequence of clinic visit dates, event counts corresponding to the successive time intervals between clinic visits, and baseline covariates. We propose a semiparametric regression model, extending the fully parametric model of Thall (1988, Biometrics 44, 197-209), to estimate and test for covariate effects on the rate of events over time while also accounting for the possibly time-varying nature of the underlying event rate. Covariate effects enter the model parametrically, while the underlying time-varying event rate is modelled nonparametrically. The method of Severini and Wong (1992, Annals of Statistics 20, 1768-1802) is used to construct asymptotically efficient estimators of the parametric component and to specify their asymptotic distribution. A simulation study and application to a data set are provided.

Biometry↗

PubMed2004

Inherent bias toward the null hypothesis in conventional multipoint nonparametric linkage analysis.

Traditional nonparametric "multipoint" statistical procedures have been developed for assigning allele-sharing values at a locus of interest to pairs of relatives for linkage studies. These procedures attempt to accommodate a lack of informativity, nongenotyped loci, missing data, and related issues concerning the genetic markers used in a linkage study. However, such procedures often cannot overcome these phenomena in compelling ways and, as a result, assign relevant relative pairs allele-sharing values that are "expected" for those pairs. The practice of assigning expected allele-sharing values to relative pairs in the face of a lack of explicit allele-transmission information can bias traditional nonparametric linkage test statistics toward the null hypothesis of no locus effect. This bias is due to the use of expected values, rather than to a lack of information about actual allele sharing at relevant marker loci. The bias will vary from study to study on the basis of the DNA markers, sample size, relative-pair types, and pedigree structures used, but it can be extremely pronounced and could contribute to a lack of consistent success in the application of traditional nonparametric linkage analyses to complex human traits and diseases. There are several potential ways to overcome this problem, but their foundations deserve greater research. We expose many of the issues concerning allele sharing with data from a large affected-sibling-pair study investigating the genetic basis of autism.

Alleles↗

PubMed2002

Hand-assisted laparoscopic splenectomy in patients with splenomegaly or prior upper abdominal operation.

BACKGROUND: Laparoscopic splenectomy (LS) in patients with significant splenomegaly or prior upper abdominal operation is technically challenging with a high conversion rate to open operation. We hypothesized that hand-assisted laparoscopic splenectomy (HLS) in this setting would improve operative (OR) outcomes without impacting post-OR ileus, length of stay, morbidity, or mortality, compared with LS. METHODS: All patients with splenomegaly (spleen weight > or = 500 g) or prior upper abdominal operation undergoing LS or HLS between March 1996 and June 2001 were reviewed. Nonparametric continuous variables were expressed as median and intraquartile range with statistical significance determined by Wilcoxon rank sum test. RESULTS: Of 41 patients reviewed, 22 underwent HLS, whereas 19 underwent LS. Median OR time for HLS was significantly less than for LS (161 minutes vs 212 minutes, P =.004). HLS was associated with a lower conversion rate (13.6% vs 36.8%, P =.08) and blood loss (325 mL vs 550 mL, P =.18) than LS, which approached statistical significance. HLS did not increase post-OR ileus, length of stay, morbidity, or mortality. CONCLUSIONS: HLS in patients with significant splenomegaly or prior upper abdominal operation significantly shortens OR time compared with LS without adversely impacting post-OR ileus, length of stay, morbidity, or mortality. In addition, HLS may be associated with a lower conversion rate and decreased blood loss.

Female↗

PubMed2006

Quadratic inference functions for varying-coefficient models with longitudinal data.

Nonparametric smoothing methods are used to model longitudinal data, but the challenge remains to incorporate correlation into nonparametric estimation procedures. In this article, we propose an efficient estimation procedure for varying-coefficient models for longitudinal data. The proposed procedure can easily take into account correlation within subjects and deal directly with both continuous and discrete response longitudinal data under the framework of generalized linear models. The proposed approach yields a more efficient estimator than the generalized estimation equation approach when the working correlation is misspecified. For varying-coefficient models, it is often of interest to test whether coefficient functions are time varying or time invariant. We propose a unified and efficient nonparametric hypothesis testing procedure, and further demonstrate that the resulting test statistics have an asymptotic chi-squared distribution. In addition, the goodness-of-fit test is applied to test whether the model assumption is satisfied. The corresponding test is also useful for choosing basis functions and the number of knots for regression spline models in conjunction with the model selection criterion. We evaluate the finite sample performance of the proposed procedures with Monte Carlo simulation studies. The proposed methodology is illustrated by the analysis of an acquired immune deficiency syndrome (AIDS) data set.

Acquired Immunodeficiency Syndrome↗