SEARCH · PubMed Health

Results for “Empirical Approach”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29Linked to original sources

PubMed1975

Effectiveness of achievable urinary concentrations of tetracyclines against "tetracycline-resistant" pathogenic bacteria.

Hospitalized patients with urinary tract infections caused by Pseudomonas aeruginosa or other bacterial pathogens are frequently treated with parenteral antibiotics such as gentamicin. Many of these organisms are shown by Kirby-Bauer disk sensitivity testing to be resistant to tetracycline. One hundred seventy-one such tetracycline-resistant bacterial isolates were studied; 84% were found to be sensitive to achievable urinary concentrations of tetracycline. Two patients with long-standing chronic urinary tract infection with Pseudomonas were treated with tetracycline for a year and a half with excellent results. In a pilot clinical trial, eight of 12 hospitalized patients with urinary tract infection were treated successfully with tetracycline without regard to disk sensitivity data. Institution of tetracycline as soon as the microscopic diagnosis of urinary tract infection is made might be an acceptable empiric approach to the treatment of urinary infection in hospitalized patients who do not show evidence of sepsis.

Bacteriuria↗

PubMed1994

Equality, explicitness, severity, and rigidity: the Oregon plan evaluated from a Scandinavian perspective.

This article is an attempt to evaluate the Oregon plan from the perspective of a Scandinavian national health care system. The Nordic welfare states are marked by a strong emphasis on equality. As an example of an egalitarian system we present the Norwegian health care model in part one. In part two, the arguments in favor of a one tier system in Norway are presented and compared to Oregon's two tier system. Although we argue, in part three, that a comparison of the degree of explicitness in the prioritization process shows that Norway has much to learn from Oregon, we do believe that the Norwegian system has some attractive elements that may function as an important corrective. In part four we present the Norwegian Guidelines for priority-setting and discuss the weight assigned to the severity of disease criterion. It is argued that the exclusion of information about the severity of disease partly explains the counterintuitive ranking of treatment-condition pairs in Oregon's initial method based on the principle of health maximization. A normative analysis of the conflicting norms of efficiency and equality of results is called for. The final part of the paper is devoted to the problem of rigidity. Henry J. Aaron has argued that the Oregon system is insensitive to inter-individual variations within each diagnosis-treatment pair. This objection is a severe one, since the system might end up treating patients unfairly on the individual level. To overcome this problem, we suggest a selection rule that should be more capable of dealing with the problem of rigidity.

Community Participation↗

PubMed1992

Introduction to modeling.

A model is a representation of structure and a mathematical model describes mathematically the relationship between variables and/or parameters. Numerous types of mathematical models have been used to study biological systems that are of interest to nutritionists. This paper introduces some concepts that relate to the dynamic behavior of biological systems and discusses two modeling approaches that can be used in conjunction with kinetic studies. The two approaches, empirical compartmental modeling and model-based compartmental analysis, are subcategories of compartmental analysis. The objective of this brief introduction to modeling is to encourage more nutritionists to use compartmental analysis and other forms of mathematical modeling in their research.

Animals↗

PubMedDate not supplied

The Wilhelmine E. Key 1994 invitational Lecture. Plant genetic diversity and the struggle to measure selection.

The fundamental research program of population genetics has been to seek a quantitative assessment of the role of the various forces of evolution in shaping patterns of genetic variation. This goal has been pursued on both empirical and theoretical fronts. The introduction of biochemical and molecular techniques into population genetics more than 25 years ago revealed vast stores of genetic variation within populations. This level of genetic diversity is difficult to reconcile with balancing selection, and as a consequence, recent thinking has emphasized the role of mutation and genetic random drift as the primary determinants of genetic diversity. The resulting neutral theory of molecular evolution has dominated population genetic thought for more than 20 years. Nonadaptive theories have also emphasized the role of deleterious mutations in driving evolutionary change. New insights into the relative importance of selection and genetic random drift can now be obtained from samples of DNA sequences of genes drawn from within species. The elaboration of coalescence theory, together with the accumulation of data on gene genealogies, permits an integration over relatively long periods of evolutionary time. The ability to integrate over long periods of evolutionary time permits the detection of small selection intensities and it reveals some information about the mode of selection. When the genealogy is consistent with a neutral process, the effective population size can be estimated, as can the age of the coalescent, thus providing new empirical approaches to the estimation of these important parameters. Applications of these approaches in plant population genetics are still in their infancy, but they have already provided new insights into effective population sizes and they are beginning to illustrate how selection for domestication has affected plant genomes.

Chromosome Mapping↗

PubMed2002

Biological weighting of absorbed dose in radiation therapy.

Absorbed dose is a quantity which is scientifically rigorously defined and used to quantify the exposure of biological objects, including humans, to ionising radiation. There is, however, no unique relationship between absorbed dose and induced biological effects. The effects induced by a given absorbed dose to a given biological object depend also on radiation quality and temporal distribution of the irradiation. In radiation therapy, empirical approaches are still used today to account for these dependencies in practice. In hadron therapy (neutrons, protons, ions), radiation quality is accounted for with a diversity of (almost hospital specific) methods. The necessity to account for temporal aspects is well known in external beam therapy and in high dose rate brachytherapy. The paper reviews the approaches for weighting the absorbed dose in radiation therapy, and focusses on the clinical aspects of these approaches, in particular the accuracy requirements.

Absorption↗

PubMedDate not supplied

Long-term growth and water balance predictions for a mountain ash (Eucalyptus regnans) forest catchment subject to clear-felling and regeneration.

We used a physically based ecohydrological model to predict the water balance and growth responses of a mountain ash (Eucalyptus regnans F. Muell.) forest catchment to clear-felling and regeneration. The model, Topog-IRM, was applied to a 0.53 km(2) catchment for a 3-year pretreatment period, and a 20-year period following clear-felling and reseeding of 78% of the catchment area. Simulations were evaluated by comparing observed and predicted streamflows, rainfall interception and soil water values. The model faithfully simulated observed temporal patterns of overstory live stem carbon gain and produced a leaf area trajectory consistent with field observations. Cumulative throughfall was predicted within 1% of observations over an 18-year period. Over a 4-year period, predicted soil water storage in the upper 1.5 m of soil agreed well with field observations. There was fair correspondence between observed and predicted daily streamflows, and the model explained 76% of the variation in monthly flows. Over the 23-year simulation period, the model overpredicted cumulative streamflow by 6%. We argue that there is a useful role for physically based ecohydrological models in the management of mountain ash forest catchments that cannot be satisfied by simple empirical approaches.

Journal Article↗

PubMed2003

A method for describing the canopy architecture of coppice poplar with allometric relationships.

A multi-scale biometric methodology for describing the architecture of fast-growing short-rotation woody crops is used to describe 2-year-old poplar clones during the second rotation. To allow for expressions of genetic variability observed within this species (i.e., growth potential, leaf morphology, coppice and canopy structure), the method has been applied to two clones: Ghoy (Gho) (Populus deltoides Bartr. ex Marsh. x Populus nigra L.) and Trichobel (Tri) (Populus trichocarpa Torr. & A. Gray x Populus trichocarpa). The method operates at the stool level and describes the plant as a collection of components (shoots and branches) described as a collection of metameric elements, themselves defined as a collection of elementary units (internode, petiole, leaf blade). Branching and connection between the plant units (i.e., plant topology) and their spatial location, orientation, size and shape (i.e., plant geometry) describe the plant architecture. The methodology has been used to describe the plant architecture of 15 selected stools per clone over a 5-month period. On individual stools, shoots have been selected from three classes (small, medium and large) spanning the diameter distribution range. Using a multi-scale approach, empirical allometric relationships were used to parameterize elementary units of the plant, topological relationships and geometry (e.g., distribution of shoot diameters on stool, shoot attributes from shoot diameter). The empirical functions form the basis of the 3-D Coppice Poplar Canopy Architecture model (3-D CPCA), which recreates the architecture and canopy structure of fast-growing coppice crops at the plot scale. Model outputs are assessed through visual and quantitative comparisons between actual photographs of the coppice canopy and simulated images. Overall, results indicate a good predictive ability of the 3-D CPCA model.

Imaging, Three-Dimensional↗

PubMed1997

Pharmacokinetic study of three synthetic AT-binding pentasaccharides in various animal species-extrapolation to humans.

The 'synthetic pentasaccharide', SR 90107A/Org 31540 (SP) representing the minimal AT-binding sequence of heparin is a catalyst of factor Xa inhibition. Affinity of SP, Sanorg 32701 (32701) and SR 80027 (80027), two close analogues of SP for rat, rabbit, baboon and human AT has been evaluated. The dissociation constants (Kd) for AT of the three species were in the range of 41-132, 1.4-6.2 and 2.8-4.6 nM for SP, 80027 and 32701, respectively. Comparative pharmacokinetics (PK) of their anti-factor Xa activities were determined in rats, rabbits and baboons. An apparent correlation could be demonstrated between half-lives of elimination and the corresponding Kd for AT in rats and rabbits whereas in baboons, such a correlation was not found. These results showed that despite Kd values ten times lower for 32701 than for SP, both compounds showed close PK parameters in baboons whereas the very low Kd value for 80027 was associated with an extended terminal half-life in this species. The predicted human PK parameters were determined using an allometric model: an empirical approach based on the integration of data obtained in various animal species which allows the extrapolation to humans. The values obtained for the terminal half-lives of SP, 80027 and 32701 were 14.1, 88 and 6.5 h, respectively. For SP, calculation by allometry correlated well with the values observed in man. Since knowledge of duration of activity is pivotal for appropriate design of phase I clinical studies of anti-Xa oligosaccharides, allometry appears to be an interesting tool to predict the duration of action of such compounds in man.

Animals↗

PubMed1980

Evaluating a clinical psychiatry course using process and outcome measures.

An empirical approach was taken in evaluating training in experiences and outcomes in a second-year psychiatry clerkship. A biweekly activity summary provided a detailed record of actual training experiences, didactic and clinical, and is presented as a model for use in other program evaluations. Statistically significant preclerkship changes occurred on most attitude and all perceived skill measures. Scores on the examination of the National Board of Medical Examiners were well above average. Satisfaction measures were favorable and correlated significantly with the overall attitudinal and perceived skill changes. Comparisons among outcome measures showed that attitudinal and skill dimensions correlated with each other and with satisfaction ratings, but they did not correlate with scores on an objective examination.

Attitude↗

PubMed1994

Educating medical students: lessons from research in continuing education.

Creating a true continuum of medical education from admission to medical school throughout a lifetime of professional learning is easier said than done. To do so, the various components on the continuum must be explored to determine where appropriate links might be made. The author considers selected concepts and evidence from the theory and practice underlying continuing medical education (CME) and continuing professional education (CPE) insofar as CME and CPE can inform undergraduate medical curricula, including its current innovations. Five conceptual and empirical approaches from CME and CPE are discussed in detail: social learning theory, how physicians learn and change, competence in business and the professions, how professionals learn in practice, and lifelong self-directed learning. Then the author describes the implications of these approaches for the ongoing development of undergraduate medical education. (1) The entire learning environment, and not merely discrete aspects such as curriculum content, must be examined and fully utilized to benefit learning. (2) The importance of the contexts in which learning occurs must be emphasized in several ways. (3) Learning should be centered around clinical problems. (4) The many benefits of small-group learning and other ways of learning from colleagues should be emphasized. (5) The undergraduate curriculum should emphasize the development of students' feelings of self-efficacy to ensure that students become physicians who are confident about their abilities. (6) CME research and CPE research reinforce the efforts in undergraduate medical education to emphasize the early development of students' process skills as well as content mastery.

Education, Medical, Continuing↗

PubMed2002

Prospective study of etiologic agents of community-acquired pneumonia in patients with HIV infection.

OBJECTIVES: To study prospectively HIV-positive patients admitted to the hospital because of pneumonia by extensive laboratory tests to determine specific microbiologic diagnoses and to establish the best clinical diagnosis after review of all available data by expert clinicians. METHODS: Patients admitted to one of two hospitals had extensive questionnaires completed and defined diagnostic tests performed on blood, sputum, urine and bronchoalveolar lavage specimens, when available. RESULTS: A total of 230 patients had a diagnosis of pneumonia verified. A definite or probable etiologic diagnosis was made in 155 (67%) of these patients. Pneumocystis carinii caused 35% of all cases of pneumonia. Twenty-seven percent of cases of pneumonia with a single etiology had a definite or probable bacterial etiology. 'Atypical agents' were distinctly uncommon. Few clinical or laboratory parameters could differentiate specific etiologies. CONCLUSIONS: P. carinii continues to be a common cause of pneumonia in these patients. The rarity of 'atypical agents' could simplify the empiric approach to therapy. Despite the use of extensive testing we did not find a definite etiology in a large number of cases.

AIDS-Related Opportunistic Infections↗

PubMed1980

Preoperative pharmacology and anesthetic risk.

Chronic or preoperative drug therapy may contribute to the overall risk of anesthesia by modifying organ function directly, or by altering the response of the patient to anesthetic agents or adjuvants. Many drug-patient and drug-drug interactions can be predicted from analysis of their expected effects upon the neurohumoral control systems that normally maintain physiological homeostasis, especially those involving the release or termination of action of catecholamines or acetylcholine. Current concepts of biotransformation, especially as regards hepatic microsomal function, are so broad that estimates of the toxic potential of the metabolites of anesthetic drugs still require an empirical approach for each agent considered.

Anesthetics↗

PubMed1990

Comparison of DSM-III and DSM-III-R diagnoses for prepubertal children: changes in prevalence and validity.

A structured and reliable diagnostic procedure based on a revised version of the Diagnostic Interview Schedule for Children for children, parents, and teachers was used to assign both DSM-III and DSM-III-R diagnoses to 177 outpatient boys aged 7 to 12 years. Compared to their DSM-III counterparts, DSM-III-R oppositional defiant disorder was 25.5% less prevalent, DSM-III-R dysthymia was 37.8% less prevalent, and DSM-III-R conduct disorder (CD) was 44.3% less prevalent. However, DSM-III-R attention deficit hyperactivity disorder was 14.4% more prevalent than DSM-III attention deficit disorder with hyperactivity. The two definitions of CD were compared to exemplify an empirical approach to diagnostic validation. The DSM-III-R diagnosis of CD appears to be more valid as it is more strongly associated with police contacts, school suspensions, and history of antisocial personality disorder in the biological father, but both CD diagnoses are associated with family histories of criminal convictions.

Child↗

PubMed1999

Latent class analysis of Child Behavior Checklist attention problems.

OBJECTIVE: To test whether attention problems in children are continuously distributed or categorically discrete, the authors performed latent class analyses (LCA) of items from the Attention Problems scale of the Child Behavior Checklist (CBCL) using data from the clinical and nonclinical samples used in the derivation of the CBCL syndromes. METHOD: A CBCL was completed by a parent or guardian of each of 2,100 nonreferred children selected to be representative of U.S. nonreferred children and a demographically matched sample of 2,100 clinically referred children. Attention problems symptoms were subjected to LCA. RESULTS: LCAs were consistent with the presence of 3 levels of symptom presentation in both samples. Children in the nonclinical sample were classified as having no symptoms, mild symptoms, or moderate symptoms. Children in the clinical group had mild, moderate, or severe symptoms. CONCLUSIONS: These results suggest that child and adolescent psychiatric symptoms such as attention problems can be thought of as continuously distributed phenomena rather than discrete disease entities, lending support for an empirical approach to both clinical work and research. In addition, high prevalence rates of attention problems in both clinical and nonclinical samples suggest the need for careful screening of attention problems in clinic and academic settings.

Adolescent↗

PubMed1988

Identifying catastrophic psychiatric cases. Targeting managed-care strategies.

Case management programs, a specialized form of utilization review (UR), focus their interventions on catastrophic cases, which comprise the minority of patients while accounting for the majority of costs. Many case management programs base their case identification and review criteria on diagnosis alone, although research has shown that it is a poor predictor of length of stay. Using claims data from a large nationwide insurer, the authors developed an empirical approach to identifying potentially catastrophic cases. The findings suggest that, in addition to diagnosis, other factors such as age and treatment setting contribute to long stays and high costs and thus should be used to identify catastrophic cases for case management interventions. Strategies to target case management programs must be considered not only in light of their impact on cost but on the quality of care for individual patients.

Adolescent↗

PubMed2001

Post-surgical ablation of thyroid remnants with high-dose (131)I in patients with differentiated thyroid carcinoma.

The aims of this study were to evaluate the efficacy of an empirically determined "fixed" high ablative dose of radioiodine ((131)I) therapy and to determine the utility of ultrasonography (US) in dose determination. A retrospective analysis was performed of 242 thyroid cancer cases treated with "fixed" high-dose (131)I for ablation of thyroid remnants without a pre-ablative (131)I diagnostic scintigraphy or radioiodine uptake study. Treatment doses ranged from 1850 MBq (50 mCi) to 7.4 GBq (200 mCi). The selection of the treatment dose was based on the surgical and pathological findings as well as the remnant thyroid volume calculated by US. A successful ablation was defined as the absence of activity in the thyroid bed on subsequent imaging studies. Successful ablation was obtained in 218 of the 242 patients (90%). In 162 of the 218 patients (74.3%), successful ablation was achieved after a single (131)I treatment. The remnant thyroid volume calculated by US was significantly different (P=0.04) between those who were successfully ablated and those who were not. The total (131)I dose needed for successful ablation was significantly higher in males (P=0.003). Patients with higher post-operative thyroglobulin (Tgb) levels and patients with a higher stage of disease required higher doses (P=0.036 and P=0.021 respectively). Serum Tgb levels were under 10 ng.ml(-1) in 220 of the 242 patients (90%) following radioiodine ablation while not receiving L-thyroxine suppression. Nineteen patients (7.8%) showed metastases on post-therapy scan and successful treatment was achieved in 11 of 19 (57.8%). Four of the 19 patients with distant metastases (revealed on post-treatment scan) were found to have been given a treatment dose of less than 200 mCi based on the proposed empirical approach. These results indicate that "fixed" high-dose (131)I treatment is clinically feasible with an acceptable dose underestimation rate, and the utilization of US in the determination of the thyroid remnant volume provides more accurate and reproducible results.

Adult↗

PubMed2001

Use of antimicrobials to prevent postoperative infection in patients with cataracts.

Despite the high frequency of cataract surgery, there are still no definitive studies on antibiotic prophylaxis against endophthalmitis after cataract surgery. Most surgeons follow an empiric approach. The results of several recent studies shed additional light on this complex topic. There is better knowledge of the usual source of the infection and the specific organisms incriminated. This review presents some principles of prophylactic treatment and selected literature that addresses the effectiveness of antisepsis, topical preoperative antibiotics, intracameral antibiotics, subconjunctival antibiotics, systemic antibiotics, and postoperative antibiotics. The worldwide problem of antibiotic resistance should temper our approach. Some organizational statements are reviewed, and personal recommendations are offered. Controversy still abounds.

Anti-Infective Agents↗

PubMed2007

Generation of calibrated tungsten target x-ray spectra: modified TBC model.

In spite of the recent advances in the experimental detection of x-ray spectra, theoretical or semi-empirical approaches for determining realistic x-ray spectra in the range of diagnostic energies are important tools for planning experiments, estimating radiation doses in patients, and formulating radiation shielding models. The TBC model is one of the most useful approaches since it allows for straightforward computer implementation, and it is able to accurately reproduce the spectra generated by tungsten target x-ray tubes. However, as originally presented, the TBC model fails in situations where the determination of x-ray spectra produced by an arbitrary waveform or the calculation of realistic values of air kerma for a specific x-ray system is desired. In the present work, the authors revisited the assumptions used in the original paper published by . They proposed a complementary formulation for taking into account the waveform and the representation of the calculated spectra in a dosimetric quantity. The performance of the proposed model was evaluated by comparing values of air kerma and first and second half value layers from calculated and measured spectra by using different voltages and filtrations. For the output, the difference between experimental and calculated data was better then 5.2%. First and second half value layers presented differences of 23.8% and 25.5% in the worst case. The performance of the model in accurately calculating these data was better for lower voltage values. Comparisons were also performed with spectral data measured using a CZT detector. Another test was performed by the evaluation of the model when considering a waveform distinct of a constant potential. In all cases the model results can be considered as a good representation of the measured data. The results from the modifications to the TBC model introduced in the present work reinforce the value of the TBC model for application of quantitative evaluations in radiation physics.

Calibration↗