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PubMed2006

Effect of gender and visit length on participation in pediatric visits.

OBJECTIVE: To examine the effect of child, physician and parent genders as well as visit length on participation. METHODS: We analyzed videotapes and sociodemographics from 100 pediatric visits. Using the Roter Interaction Analysis System, coded utterances were aggregated to reflect key visit tasks: information giving, information gathering and relationship building. Negative binomial models were used to analyze how participation was associated with participants' genders and visit length. RESULTS: After adjustment, girls did twice as much relationship building as boys (incidence rate ratio = 2.33, 95% confidence interval = 1.01-5.36) and their physicians did 34% more information gathering (1.34, 1.16-1.55). Female physicians did 29% less information giving (0.71, 0.54-0.94). Having the father accompany the child reduced child relationship building 76% (0.24, 0.08-0.69) and reduced physician information giving 14% (0.86, 0.75-0.995), compared to having mother accompany. After adjusting for participants' genders, longer visits were associated with more participation for all participants. CONCLUSION: Child participation was impacted by child gender and by the accompanying parent's gender as well as the visit length. PRACTICE IMPLICATIONS: Because gender-based patterns of participation are evident in childhood, interventions to facilitate participation might begin early in life. To improve participation, interventions might include advocating for policies to support longer visit lengths.

Adolescent↗
PubMed2005

On the surveillance for animal diseases in small herds.

Small herds may present a problem in surveillance for infectious animal diseases because typical levels of a within-herd design prevalence are not directly applicable. We suggest a definition of small herds as those smaller than 2/(within-herd design prevalence) on the basis that such herds would be expected to have less than two (i.e. only one) infected animals. Consequently, the probability of detecting small herds cannot be improved by choosing a larger sample size within the herd. We derive necessary sample sizes of herds and the probability ("confidence") of detecting disease within a stratum of small herds, given the among-herd design prevalence and test diagnostic sensitivity. Both a binomial model and a Poisson model can be used to establish the confidence for a given sample size of herds (and vice versa). The results of a simulation study suggest that the Poisson model provides more conservative (lower) estimates of the confidence for a given sample size and should therefore be preferred.

Animal Diseases↗
PubMed2001

Overdispersion in modelling accidents on road sections and in empirical bayes estimation.

In multivariate statistical models of road safety one usually finds that the accident counts are 'overdispersed'. The extent of the overdispersion is itself subject to estimation. It is shown that the assumption one makes about the nature of overdispersion will affect the maximum likelihood estimates of model parameters. If one assumes that the same overdispersion parameter applies to all road sections in the data base, then, the maximum likelihood estimate of parameters will be unduly influenced by very short road sections and insufficiently influenced by long road sections. The same assumption about the overdispersion parameter also leads to an inconsistency when one estimates the safety of a road section by the Empirical Bayes method. A way to avoid both problems is to estimate an overdispersion parameter (phi) that applies to a unit length of road, and to set the overdispersion parameter for a road section of length L to phiL. How this would change the estimates of regression parameters for road section models now in use requires examination. Safety estimation by the Empirical Bayes method is altered substantially.

Accidents, Traffic↗
PubMed2003

Applying the random effect negative binomial model to examine traffic accident occurrence at signalized intersections.

Poisson and negative binomial (NB) models have been used to analyze traffic accident occurrence at intersections for several years. There are however, limitations in the use of such models. The Poisson model requires the variance-to-mean ratio of the accident data to be about 1. Both the Poisson and the NB models require the accident data to be uncorrelated in time. Due to unobserved heterogeneity and serial correlation in the accident data, both models seem to be inappropriate. A more suitable alternative is the random effect negative binomial (RENB) model, which by treating the data in a time-series cross-section panel, will be able to deal with the spatial and temporal effects in the data. This paper describes the use of RENB model to identify the elements that affect intersection safety. To establish the suitability of the model, several goodness-of-fit statistics are used. The model is then applied to investigate the relationship between accident occurrence and the geometric, traffic and control characteristics of signalized intersections in Singapore. The results showed that 11 variables significantly affected the safety at the intersections. The total approach volumes, the numbers of phases per cycle, the uncontrolled left-turn lane and the presence of a surveillance camera are among the variables that are the highly significant.

Accidents, Traffic↗
PubMed1997

Modeling accident frequencies as zero-altered probability processes: an empirical inquiry.

This paper presents an empirical inquiry into the applicability of zero-altered counting processes to roadway section accident frequencies. The intent of such a counting process is to distinguish sections of roadway that are truly safe (near zero-accident likelihood) from those that are unsafe but happen to have zero accidents observed during the period of observation (e.g. one year). Traditional applications of Poisson and negative binomial accident frequency models do not account for this distinction and thus can produce biased coefficient estimates because of the preponderance of zero-accident observations. Zero-altered probability processes such as the zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) distributions are examined and proposed for accident frequencies by roadway functional class and geographic location. The findings show that the ZIP structure models are promising and have great flexibility in uncovering processes affecting accident frequencies on roadway sections observed with zero accidents and those with observed accident occurrences. This flexibility allows highway engineers to better isolate design factors that contribute to accident occurrence and also provides additional insight into variables that determine the relative accident likelihoods of safe versus unsafe roadways. The generic nature of the models and the relatively good power of the Vuong specification test used in the non-nested hypotheses of model specifications offers roadway designers the potential to develop a global family of models for accident frequency prediction that can be embedded in a larger safety management system.

Accidents, Traffic↗
PubMed1998

Heterogeneity considerations in accident modeling.

Panel data sets are becoming readily available and increasingly popular in safety research. Despite its advantages, panel data raises new specification issues, the most important of which is heterogeneity, which have not been addressed in previous studies in the safety area. Based on a county accident data set, the present analysis extends prior research in a significant direction. There is an explicit effort to control for cross-section heterogeneity that may otherwise seriously bias the resulting estimates and invalidate statistical tests. Because common modeling techniques such as the fixed and random effects models, developed to account for heterogeneity, are impractical for count data, this study uses cluster analysis to overcome this. First, observations are disaggregated into homogeneous clusters. Then, separate negative binomial models including a time trend factor are developed for each group. The results clearly indicate that there are significant differences between the models developed, and that separate models describe data more efficiently than the joint model.

Accidents, Traffic↗
PubMed2000

Modeling traffic accident occurrence and involvement.

The Negative Binomial modeling technique was used to model the frequency of accident occurrence and involvement. Accident data over a period of 3 years, accounting for 1,606 accidents on a principal arterial in Central Florida, were used to estimate the model. The model illustrated the significance of the Annual Average Daily Traffic (AADT), degree of horizontal curvature, lane, shoulder and median widths, urban/rural, and the section's length, on the frequency of accident occurrence. Several Negative Binomial models of the frequency of accident involvement were also developed to account for the demographic characteristics of the driver (age and gender). The results showed that heavy traffic volume, speeding, narrow lane width, larger number of lanes, urban roadway sections, narrow shoulder width and reduced median width increase the likelihood for accident involvement. Subsequent elasticity computations identified the relative importance of the variables included in the models. Female drivers experience more accidents than male drivers in heavy traffic volume, reduced median width, narrow lane width, and larger number of lanes. Male drivers have greater tendency to be involved in traffic accidents while speeding. The models also indicated that young and older drivers experience more accidents than middle aged drivers in heavy traffic volume, and reduced shoulder and median widths. Younger drivers have a greater tendency of being involved in accidents on roadway curves and while speeding.

Accidents, Traffic↗
PubMed2002

Interpreting and using the dietary references intakes in dietary assessment of individuals and groups.

For individuals, a statistical approach is available to compare observed intakes to the EAR or AI (to assess adequacy), and the UL (to assess risk of excess). A more qualitative assessment of intakes involves comparison directly to the RDA to evaluate adequacy, but this is accurate only if long-term usual intake is known. For groups of people, the prevalence of inadequacy can usually be estimated as the proportion with intakes below the EAR, while the prevalence of potentially excessive intakes is estimated as the proportion above the UL. The accuracy of all assessments depends on unbiased and accurate intake estimates as well as a consideration of the effects of day-to-day variation in intake. Nutrition practitioners will find the new DRIs useful for assessing diets in a variety of settings. Computerized assessment systems will be important tools when incorporating these theoretical concepts into dietetic practice.

Binomial Distribution↗
PubMed1998

In vitro Doppler assessment of pressure gradients across modified Blalock-Taussig shunts.

The relation between flow velocity and the pressure decrease is evaluated in Blalock-Taussig shunts used in congenital heart surgery and is related to the flow conditions and geometries of the shunts studied. The authors propose that the flow conditions within the shunt as well as shunt dimensions need to be taken into account when using Doppler velocimetry to predict pressure drops across these shunts.

Adolescent↗
PubMed1991

Effect of porcelain crown substructures on visually perceivable value.

Factors that will affect the potential color of ceramic restorations must be understood to control variables that exist. Clinical observations of porcelain restorations lead to the hypothesis that certain substructures tend to produce crowns with a lower than expected Value (brightness). This study was done to determine whether a visually perceivable difference could be detected between groups of ceramic crowns with different substructures. Two test groups of crown types with four different porcelain substructures were compared. In the first group, metal ceramic crowns made with either Galaxy or Rexillium III alloys were compared. In the second group, aluminous porcelain jacket crowns with and without a tin-plated, bonded platinum foil internally were compared. Visual analysis showed that (1) in the metal ceramic group, the crowns with the Rexillium III substructure were scored as more often having a lower significant Value, and (2) in the aluminous porcelain jacket group the crowns with the tin-plated, bonded platinum substructures were scored as more often having a lower significant Value.

Binomial Distribution↗
PubMed1990

A stratified binomial marker model for bone-marrow repopulation experiments.

The paper considers bone-marrow repopulation experiments with injected mixtures of two types, A and B, of genetically marked donor cells. The covariance of the proportions of type A erythrocytes and lymphocytes is analysed as the sum of two components, under a stratified binomial model allowing the proportions of type A cells to vary in postulated strata of the mixture and with the assumption that the genetic marker does not influence cell development. The ratio of the two components is not experimentally estimable, but each of them has an interesting "demographic" interpretation. Possible inferences about certain "two-cell probabilities" are derived, and the experimental findings that necessitated the stratified model are illustrated.

Animals↗
PubMed2001

Bernoulli excitation and detection of gas bubbles.

A simple method is proposed for detecting and sizing bubbles in pipeline fluid flow. This is based on changing the pressure of the fluid, which in turn excites volume oscillations in the bubble. If the change in pressure is of sufficient brevity and magnitude, the transient distortion results in excitation of the bubble into radiative oscillation at its natural frequency. In a moving fluid, the Bernoulli equation predicts that such a pressure change can be achieved through a suitable gradient in the flow velocity. In the experiments described here, this is achieved by altering the cross-sectional area of the pipe in which the fluid is flowing. We demonstrate the efficacy of this excitation method and, by detecting the radiated sound using a nearby hydrophone, determine the size of individual bubbles from their characteristic oscillation frequency.

Acoustics↗
PubMed2001

Neural synergy in visual grouping: when good continuation meets common fate.

A modified version of the 'path finder' display consisting of many small oriented Gabor patches was used to study the joint contributions of spatial and temporal structures to shape perception. A two-interval forced-choice procedure measured detectability of curved 'paths' defined by orientation ('good continuation') and/or by temporal synchrony of change in motion direction ('common fate'). When orientation was completely random (no spatial 'path' cue) temporal synchrony still supported reliable performance, but only when correlation of change among 'path' elements was high. When combined, these two weak spatial and temporal structures yielded performance in excess of probability summation: 'paths' weakly defined by orientation were highly conspicuous when the constituent Gabors underwent synchronized changes in direction of motion, even though the individual directions of path elements were uncorrelated. Spatial grouping from temporal structure may arise from correlated transients associated with synchronized changes in motion direction. Evidently these two mechanisms for promotion of spatial grouping interact synergistically.

Binomial Distribution↗
PubMed2002

Ocular dominance in extrastriate cortex of strabismic amblyopic cats.

Ocular dominance in extrastriate visual cortex of cats with behaviorally defined strabismic amblyopia was studied using extracellular recording techniques. In area 18, the amblyopic eye drove about as many cells as the normal one. In area posteromedial lateral suprasylvian area (PMLS), about 60% of the cells responded exclusively to stimulation of the normal eye and 30% to stimulation of the amblyopic eye. In area 21a more than 75% of the cells were monocularly driven by the non-amblyopic eye while only 5% were monocularly driven by the amblyopic eye. These findings suggest that ventral pathways (area 21a) are more affected in amblyopia than dorsal pathways (area PMLS).

Amblyopia↗
PubMed1997

A SAS macro for constructing simultaneous confidence intervals for multinomial proportions.

Quesenberry and Hurst (1964), Goodman (1965) and Fitzpatrick and Scott (1987) proposed simultaneous construction of confidence intervals for multinomial proportions, however. statistical computing packages do not generally give one the option of specifying the type of construction to be used. We have written a SAS macro using PROC IML that takes multinomial cell counts as input and returns simultaneous confidence intervals with the user-specified coverage probability. Two main features of the macro are its ease of use and its flexibility in allowing the user to choose among six methods of constructing confidence intervals for multinomial proportions. Based on simulation May and Johnson (1997) recommended the intervals proposed by Goodman (1965) in most practical applications.

Binomial Distribution↗
PubMed1999

Identification of Chlamydia trachomatis in the human temporomandibular joint.

PURPOSE: Reactive arthritis (ReA) as a consequence of triggering Chlamydia trachomatis infections has been extensively studied to better understand inflammatory arthritis. This study investigated whether the presence of C trachomatis can be shown in the TMJ of patients with internal derangement. PATIENTS AND METHODS: Posterior bilaminar tissue removed from 31 patients (29 F, 2 M) during TMJ articular disc repositioning and posterior ligament repair was tested for the presence of C trachomatis. Cryosections were stained using a monoclonal antibody that identifies all chlamydial serovars. Highly specific polymerase chain reaction (PCR) assays independently targeting two genes of C trachomatis also were performed; these assays also identify all serovars of this organism. RESULTS: TMJ tissue from 6 of 30 patients (20%) showed the presence of C trachomatis in the posterior bilaminar tissue on immunostaining. PCR screening identified 12 of 31 patients (39%) as having C trachomatis DNA in tissue, including four of six positive by immunostaining. All chlamydia-positive patients were female, with an average age of 36.7 years (15 to 48 years). CONCLUSIONS: The presence of C trachomatis in the human TMJ has not been previously shown. The presence of this organism may serve as the pathogenetic mechanism for TMJ dysfunction, as demonstrated in other joints. Nonapparent chlamydial infection in females may also explain the marked prevalence of TMJ symptoms in women.

Adolescent↗
PubMed1998

Intrasound vibration in the early diagnosis of scaphoid fracture.

A prospective trial was designed to assess the sensitivity and specificity of intrasound vibration for the early detection of scaphoid fracture. We replicated the method described by Finkenburg et al. (J Hand Surg 1993;18A:4-7) in an attempt to corroborate their results. We found the test to be 73% sensitive and 51% specific. Because the test was not 100% sensitive, as claimed by Finkenburg et al., we discontinued the use of this device in our hospital.

Binomial Distribution↗
PubMed1992

Hydrodynamic analysis of intraocular pressure changes during anterior chamber procedures.

Variations in intraocular pressure (IOP), observed by us and other authors in closed-system anterior chamber procedures, are explained using a simple hydrodynamic analysis based on the Bernoulli equation. Calculations show that the sudden increases in IOP (pressure spikes) measured during anterior segment surgery are due primarily to the small size of the infusion cannulas and are exacerbated by high infusion rates. Accurate measurement of these IOP variations requires placement of the pressure sensors in situ and is not possible by remote pressure sensing at the infusion line or the console. This work indicates that closed-system procedures could benefit from accurate monitoring of intraoperative IOP and could use these measurements for automatic IOP control during surgery.

Animals↗