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Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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At least 559 records · Page 31Linked to original sources
PubMed2004

Methods for analysis of skewed data distributions in psychiatric clinical studies: working with many zero values.

OBJECTIVE: Psychiatric clinical studies, including those in drug abuse research, often provide data that are challenging to analyze and use for hypothesis testing because they are heavily skewed and marked by an abundance of zero values. The authors consider methods of analyzing data with those characteristics. METHOD: The possible meaning of zero values and the statistical methods that are appropriate for analyzing data with many zero values in both cross-sectional and longitudinal designs are reviewed. The authors illustrate the application of these alternative methods using sample data collected with the Addiction Severity Index. RESULTS: Data that include many zeros, if the zero value is considered the lowest value on a scale that measures severity, may be analyzed with several methods other than standard parametric tests. If zero values are considered an indication of a case without a problem, for which a measure of severity is not meaningful, analyses should include separate statistical models for the zero values and for the nonzero values. Tests linking the separate models are available. CONCLUSIONS: Standard methods, such as t tests and analyses of variance, may be poor choices for data that have unique features. The use of proper statistical methods leads to more meaningful study results and conclusions.

Cross-Sectional Studies↗
PubMed2001

Increased frequency of FcgammaRIIIb-NA1 allele in periodontitis-resistant subjects in an elderly Japanese population.

Many elderly people show minimum periodontal tissue destruction, which might be partly due to genetic advantages in host immune response against periodontopathic bacteria. The human IgG Fc receptor IIIb on neutrophils bears a NA1-NA2 polymorphism. The FcgammaRIIIb-NA1 displays a more efficient interaction with IgG1- and IgG3-opsonized bacteria, compared with the FcgammaRIIIb-NA2. We investigated a 70-year-old Japanese population (n = 599) to determine whether the FcgammaRIIIb polymorphism was associated with resistance to periodontitis. Among subjects with > or = 20 teeth present, periodontitis-resistant (n = 46) and periodontitis-susceptible groups (n = 73) were selected based on the percentage of sites with > or = 4 mm probing attachment loss in the entire dentition. The FcgammaRIIIb-NA1 allotype was overrepresented in the periodontitis-resistant group, compared with the periodontitis-susceptible group (chi2 = 4.89, p = 0.03, odds ratio = 1.87, 95% CI, 1.07 to 3.28). This suggests that FcgammaRIIIb-NA1 may be associated with resistance to periodontitis.

Aged↗
PubMed2001

A new approach to enhancement of bone formation by electrically polarized hydroxyapatite.

An electrical field may affect osteogenesis. Since we found that hydroxyapatite (HA) ceramics may be polarizable, we hypothesized that electrically polarized HA may foster production of new bone in vivo. Both polarized and non-polarized HA ceramics were inserted into the subperiosteum spaces at the parietal bone area of rats. After 2, 4, and 8 weeks, the implant sites were examined histologically. Morphometric analysis revealed that new bone formation was accelerated on the negatively charged surface of the polarized HA (N-surface) at 2 weeks. The newly formed bone approached maturation at 4 weeks and was thicker on the N-surface than in the controls. By 8 weeks, newly formed bone in the controls was almost the same as that on the N-surface. These findings suggest that polarized HA is biocompatible and that bone formation on the N-surface is enhanced in the early stage of bone healing.

Animals↗
PubMed1985

The glass bead game.

Explore the source record for details and available documents.

Periodicals as Topic↗
PubMedDate not supplied

Critical appraisal of therapeutic interventions in the intensive care unit: human monoclonal antibody treatment in sepsis. Journal Club of the Hamilton Regional Critical Care Group.

Using the medical literature to solve patient problems is challenging and rewarding. For intensive care physicians, this evidence-based medicine approach is more compelling when basic critical appraisal skills are developed. We highlight the important methodological points for interpreting the literature on treatment, using a cogent example from the critical care literature--monoclonal antibody therapy in sepsis. It is likely that as we move into the 1990s, growth in the number of articles on immunotherapy in the sepsis syndrome will parallel the growth of the general biomedical literature.

Antibodies, Monoclonal↗
PubMed2002

The effect of a high-sucrose diet on dentin formation and dental caries in hyperinsulinemic rats.

A high-sucrose diet decreases dentin formation and its minerals, but the mechanisms behind the effect are largely unknown. We studied the combined and separate effects of sucrose and insulin on dentin formation and mineral metabolism in growing rats. At weaning, animals were randomized into 4 groups: control/sucrose diets both with and without external insulin (1 U/x 100 g body weight daily). After 4 weeks, we measured areas of dentin formation, numbers and areas of dentinal caries lesions, and serum and urine glucose, insulin, Ca, Na, K, and P. Exogenous insulin increased serum and urine insulin levels and decreased serum glucose level, but did not affect dentin formation or dentinal caries lesion formation or progression. A high-sucrose diet decreased dentin formation independently of insulin. The differences in serum and urine minerals between the groups were minor. The findings confirm that sucrose-diet-induced reduction in dentinogenesis is independent of insulin and loss of minerals in urine.

Analysis of Variance↗
PubMed2002

Bone strain patterns of the zygomatic complex in response to simulated orthopedic forces.

Craniofacial bone strain upon orthopedic loading has rarely been characterized, despite its fundamental importance in our understanding of the anabolic and catabolic effects of orthopedic forces. The present study tested the hypothesis that zygomatic bone strain is modulated upon loading by headgear, a device widely used in craniofacial orthopedics. Ramp forces from 0 to 50 Newtons were applied via headgear attached to the permanent maxillary first molars in four juvenile and five adult human skulls. The average peak bone strain of the juvenile temporal articular eminence was significantly higher than the adult articular eminence (p < 0.05). Contrasting bone strain patterns were identified in the zygomatic arch: tensile in its lateral surface but compressive in its medial surface. The peak bone strain of the temporal articular eminence and the zygomatic arch both depend upon loading direction. Thus, headgear-generated orthopedic forces evoke bending of the zygomatic arch and stresses of the temporal articular eminence in vitro, suggesting the need to verify whether bone strain induces in vivo bone modeling and remodeling.

Adolescent↗
PubMed2003

The effects of mandibular two-implant overdentures on nutrition in elderly edentulous individuals.

It is unclear whether mandibular implant overdentures improve the nutritional state of edentulous patients better than conventional dentures. In a randomized clinical trial, we tested for post-treatment differences in nutritional status between patients with mandibular two-implant retained overdentures and those with conventional complete dentures. Edentulous subjects (ages 65-75 yrs) received two-implant mandibular overdentures (IOD, n = 30) or conventional dentures (CD, n = 30). Measures of nutritional state were gathered before and 6 mos after treatment. Significant improvements in anthropometric parameters were detected in the IOD but not in the CD group, for percent body fat (p = 0.011) and skin-fold thickness at the biceps, subscapularis, and abdomen (p < 0.05), with significant decreases in waist circumference (p < 0.0001) and waist-hip ratio (p = 0.001). Significant increases were seen in concentrations of serum albumin (p = 0.015), hemoglobin (p = 0.01), and B12 (p = 0.01). No significant between-group differences were found. These results suggest that low-cost IOD treatment may improve the nutritional state of edentulous people.

Aged↗
PubMed2003

Quality of marginal adaptation evaluation of posterior composites in clinical trials.

The evaluation of margins of restorations in clinical trials relies on the subjective assessment of evaluators, with no instrument having been developed, let alone validated, to assist in the process. The purpose of the present study was to assess the quality of evaluations of marginal adaptation by analyzing the distribution of marginal steps rated according to clinical criteria. Replicas of 435 restorations, the marginal qualities of which had been evaluated according to modified USPHS criteria, were randomly selected from the Occlusin multi-center clinical trial program. The marginal step height in the most deteriorated area of each restoration was measured by means of a digital step-height instrument. An overlap between the steps in the restorations with A (Alfa; replacement unnecessary) and B (Bravo; replacement questionable) ratings was found to be in the range of 101 microm to 321 microm. When the steps with a height greater or less than one standard deviation of the mean were excluded, the overlap was reduced to a range of 168 micro m to 173 microm. This finding indicates a marginal height boundary between A and B ratings for marginal adaptation of 170 +/- 3 microm.

Chi-Square Distribution↗
PubMed2005

Parametric vs. non-parametric statistics of low resolution electromagnetic tomography (LORETA).

This study compared the relative statistical sensitivity of non-parametric and parametric statistics of 3-dimensional current sources as estimated by the EEG inverse solution Low Resolution Electromagnetic Tomography (LORETA). One would expect approximately 5% false positives (classification of a normal as abnormal) at the P < .025 level of probability (two tailed test) and approximately 1% false positives at the P < .005 level. EEG digital samples (2 second intervals sampled 128 Hz, 1 to 2 minutes eyes closed) from 43 normal adult subjects were imported into the Key Institute's LORETA program. We then used the Key Institute's cross-spectrum and the Key Institute's LORETA output files (*.lor) as the 2,394 gray matter pixel representation of 3-dimensional currents at different frequencies. The mean and standard deviation *.lor files were computed for each of the 2,394 gray matter pixels for each of the 43 subjects. Tests of Gaussianity and different transforms were computed in order to best approximate a normal distribution for each frequency and gray matter pixel. The relative sensitivity of parametric vs. non-parametric statistics were compared using a "leave-one-out" cross validation method in which individual normal subjects were withdrawn and then statistically classified as being either normal or abnormal based on the remaining subjects. Log10 transforms approximated Gaussian distribution in the range of 95% to 99% accuracy. Parametric Z score tests at P < .05 cross-validation demonstrated an average misclassification rate of approximately 4.25%, and range over the 2,394 gray matter pixels was 27.66% to 0.11%. At P < .01 parametric Z score cross-validation false positives were 0.26% and ranged from 6.65% to 0% false positives. The non-parametric Key Institute's t-max statistic at P < .05 had an average misclassification error rate of 7.64% and ranged from 43.37% to 0.04% false positives. The nonparametric t-max at P < .01 had an average misclassification rate of 6.67% and ranged from 41.34% to 0% false positives of the 2,394 gray matter pixels for any cross-validated normal subject. In conclusion, adequate approximation to Gaussian distribution and high cross-validation can be achieved by the Key Institute's LORETA programs by using a log10 transform and parametric statistics, and parametric normative comparisons had lower false positive rates than the non-parametric tests.

Adolescent↗
PubMed2005

The efficiency of different search strategies in estimating parsimony jackknife, bootstrap, and Bremer support.

BACKGROUND: For parsimony analyses, the most common way to estimate confidence is by resampling plans (nonparametric bootstrap, jackknife), and Bremer support (Decay indices). The recent literature reveals that parameter settings that are quite commonly employed are not those that are recommended by theoretical considerations and by previous empirical studies. The optimal search strategy to be applied during resampling was previously addressed solely via standard search strategies available in PAUP*. The question of a compromise between search extensiveness and improved support accuracy for Bremer support received even less attention. A set of experiments was conducted on different datasets to find an empirical cut-off point at which increased search extensiveness does not significantly change Bremer support and jackknife or bootstrap proportions any more. RESULTS: For the number of replicates needed for accurate estimates of support in resampling plans, a diagram is provided that helps to address the question whether apparently different support values really differ significantly. It is shown that the use of random addition cycles and parsimony ratchet iterations during bootstrapping does not translate into higher support, nor does any extension of the search extensiveness beyond the rather moderate effort of TBR (tree bisection and reconnection branch swapping) plus saving one tree per replicate. Instead, in case of very large matrices, saving more than one shortest tree per iteration and using a strict consensus tree of these yields decreased support compared to saving only one tree. This can be interpreted as a small risk of overestimating support but should be more than compensated by other factors that counteract an enhanced type I error. With regard to Bremer support, a rule of thumb can be derived stating that not much is gained relative to the surplus computational effort when searches are extended beyond 20 ratchet iterations per constrained node, at least not for datasets that fall within the size range found in the current literature. CONCLUSION: In view of these results, calculating bootstrap or jackknife proportions with narrow confidence intervals even for very large datasets can be achieved with less expense than often thought. In particular, iterated bootstrap methods that aim at reducing statistical bias inherent to these proportions are more feasible when the individual bootstrap searches require less time.

Bayes Theorem↗