Peter M. Hooper

Effects of disinfecting irreversible hydrocolloid impressions on the resultant gypsum casts. Part II : Dimensional changes

This study evaluated the effect of disinfection time (10, 30 and 60 minutes) on the dimensional changes of stone casts poured against an irreversible hydrocolloid impression material (Jeltrate). Impressions were made of a stainless steel analog of a maxillary arch. The impressions were sprayed with bleach, iodophor, phenol, and water and were stored for designated times before poured in a type IV stone (Vel-mix). The arch width, length, and depth of the vault of the resultant casts were measured by use of a contact measuring device (MicroVal) capable of measuring to 0.0001 mm. Data were analyzed with two-way analysis of variance at the 95% confidence level. Results indicated that disinfection treatment of alginate impressions with surface disinfectants did not cause significant dimensional changes in the resultant stone casts from statistical and clinical points of view.

Effects of disinfecting irreversible hydrocolloid impressions on the resultant gypsum casts. Part I : Surface quality

This study evaluated the effects of disinfection time (10, 30, and 60 minutes) on the surface quality of stone casts poured against an alginate impression material (Jeltrate). Five antimicrobial agents were tested: Sporicidin spray, sodium hypochlorite, and iodophor for spray; and Sporicidin cold sterilization solution and Cidexplus glutaraldehyde solution for immersion. Impressions, flushed with water and stored for 0, 10, 30, and 60 minutes before pouring, served as untreated controls. On completion of the disinfection treatments, the impressions were rinsed and poured in Velmix stone. The effects on cast surface were evaluated under a stereomicroscope by three experienced raters. A 1-to-4 scoring system was developed to rate the surface quality in terms of smoothness and detail reproduction. Both immersion disinfectants proved to be unacceptable for treating alginate impressions. The mean scores of other disinfectant-time combinations were compared with the use of the Tukey-Kramer method with a 95% confidence interval. The results indicated that treatment time had statistically significant effects on the quality of cast surface in Sporicidin spray, sodium hypochlorite, and untreated control groups but not in the iodophor spray group.

Factors Associated with Length of Stay in Hospital for Suspected Community-Acquired Pneumonia

OBJECTIVE To determine factors associated with the length of stay (LOS) for patients with suspected community-acquired pneumonia (CAP) who required hospitalization for treatment. STUDY DESIGN The authors studied a population-based prospective cohort of 2,757 adults with suspected CAP who were admitted over a two-year period. Logistic regression, multiple linear regression, and classification and regression trees were used to determine the factors associated with LOS. SETTING The study was conducted in two community and tertiary care hospitals, two community and secondary care hospitals, and two community hospitals in the Capital Health Region of Edmonton, Alberta. RESULTS Symptoms such as sweats, shaking chills and wheezing were associated with an LOS of seven days or shorter, whereas weight loss, functional impairment, heart, renal or neoplastic diseases and time to first dose of antibiotic were predictive of an LOS greater than seven days. Regression tree analysis indicated that rapid achievement of physiological stability was associated with a shorter LOS. The use of an indwelling urinary catheter was found to be an important determinant of LOS. CONCLUSIONS The present study found several new associations with increased LOS in patients with CAP, including functional status, time to receipt of first dose of antibiotic therapy, use of certain antibiotics, presence of a urinary catheter and the importance of time to physiological stability. An intervention targeting avoidance of urinary catheters may be associated with a shorter LOS.

Iterative Weighted Least Squares Estimation in Heteroscedastic Linear Models

This article addresses the problem of choosing weights for iterative weighted least squares estimation in heteroscedastic linear models. An asymptotically optimal method for determining weights at each iteration is derived under a Bayesian model for the variances. The method uses a compromise between model-based and model-free variance estimates. Consider a heteroscedastic linear regression model in which responses are grouped so that the variance is constant within each group. Let β denote the vector of regression parameters and let θ denote a vector of parameters determining a prior distribution for the variances. Iterative weighted least squares estimators are defined as follows. Given estimates and , calculate a weight for the ith group as a function of , the values in the ith group of the predictor variables, and the average of the squared residuals from the estimated mean responses in the ith group. Given weights, calculate the weighted least squares estimate and a new estimate . Continue until conv...

Immunocytochemical and Morphometric Studies of Gastrin-, Somatostatin- and Serotonin-Producing Cells in the Stomach and Duodenum of Patients with Acid Peptic Disorders

Gastric and duodenal biopsies from 90 patients with various acid peptic disorders-reflux esophagitis (n = 24), gastric ulcer (n = 13), duodenal ulcer (n = 47) and nonulcer dyspepsia (n = 6)-were examined. Seven patients with minimal dyspeptic symptoms and an endoscopically and histologically normal stomach and duodenum served as controls. Immunoperoxidase staining for gastrin-producing G cells, somatostatin-producing D cells and serotonin-producing EC cells was carried out on fundic, antral and duodenal biopsies, and was quantified using a Zeiss MOP Videoplan using the peroxidase-antiperoxidase technique of Sternberger. In the gastric antrum, a G:D:EC cell ratio of approximately 1.6:1:1-was observed. In the duodenum the corresponding ratio was 1:1:2.4. No significant differences were observed within any of the major diagnostic categories. Patient age, sex, duration of symptoms, smoking habits, alcohol consumption and nonsteroidal anti-inflammatory drug use had no effect on endocrine cell densities. Reduced G cell density in the descending duodenum was observed in the presence of mild duodenitis in four patients. In four patients with evidence of antral intestinal metaplastic changes, a significant increase in duodenal G cell densities was found. These results suggest that a change in the number of G, D or EC cells does not play a primary role in the pathophysiology of acid peptic disorders in the majority of patients.

Exact distribution theory for belief net responses

Bayesian belief networks provide estimates of conditional probabilities, called query responses. The precision of these estimates is assessed using posterior distributions. This paper discusses two claims and a conjecture by Kleiter (1996) concerning the exact posterior distribution of queries. The two claims provide conditions where a query has an exact beta distribution. The first claim is clarified by the following generalization. Assuming a BDe prior and complete data, a query has the same distribution under equivalent network structures. If the query can be represented as a network parameter under an equivalent structure, it must then have a beta distribution. Kleiter’s second claim is contradicted by a counter-example. His conjecture, concerning finite mixtures of beta distributions, is also disproved.

Flexible regression modeling with adaptive logistic basis functions

The author proposes a new method for flexible regression modeling of mu lti-dimensional data, where the regression function is approximated by a linear combination of logistic basis functions. The method is adaptive, selecting simple or more complex models as appropriate. The number, location, and (to some extent) shape of the basis functions are automatically determined from the data. The method is also affine invariant, so accuracy of the fit is not affected by rotation or scaling of the covariates. Squared error and absolute error criteria are both available for estimation. The latter provides a robust estimator of the conditional median function. Computation is relatively fast, particularly for large data sets, so the method is well suited for data mining applications.

Reference Point Logistic Regression and the Identification of DNA Functional Sites

Logistic regression is frequently used in pattern recognition problems to model conditional probabilities of class membership given features observed. While performing well in many applications, logistic regression is limited to a relatively simple parametric model and is often not suitable for complex applications. This article describes a generalization of logistic regression based on reference point logistic (RPL) functions; i.e., normalized exponential functions of squared distance between the vector of observed features and reference points in the feature space. This generalization is closely related to a recently developed method for constructing classification rules. RPL regression and classification methods are based on the same parametric family of functions and the same optimization technique. The methods differ primarily in their optimality criterion and interpretation. Both methods are highly flexible. By adjusting the number of reference points, the complexity of conditional probability models and classification boundaries can be adapted to the problem at hand. Comparisons are made with related techniques from statistics and neural networks. As an illustration, RPL regression is applied to the problem of identifying functional sites at the boundaries of protein coding regions in genomic DNA.

Experimental Randomization and the Validity of Normal-Theory Inference

Abstract This article examines how randomization helps to validate model-based probability statements. The asymptotic validity of normal-theory tests for means in multivariate linear models is established under general conditions. Numerical results are presented showing how randomization provides a limited degree of robustness in small experiments. The conditional relevance of randomization is also discussed. Consider the following additive model for a comparative experiment: Y = θ + GU, where Y is a vector of responses, θ is a vector of treatment effects, U is a vector of unit effects, and G is a permutation representing the assignment of treatments to units. The vector GU is obtained by using G to permute the coordinates of U. It is assumed that θ is fixed and G and U are random and independent. The experimenter observes Y and G, but not θ or U, and chooses the distribution of G, that is, the randomization strategy. In this setup, three probabilities may be considered: conditional given G, conditional g...

Invariant prediction regions with smallest expected measure

A method is given for constructing a prediction region having smallest expected measure within the class of invariant level [beta] prediction regions. The main assumptions are that the invariance group acts transitively on the parameter space and that the measure satisfies a certain invariance property. When the invariance group satisfied the Hunt-Stein Condition, the optimal invariant prediction region minimizes the maximum expected measure among all level [beta] prediction regions. Prediction regions are constructed for: a random variable with density of arbitrary given shape but unknown location and scale; several random vectors in a multivariate regression model; and order statistics of a sample from an unspecified continuous distribution.