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PubMed2005

An evidence-based review and guidelines for patient self-testing and management of oral anticoagulation.

There is a limited evidence base for self-testing and -management for oral anticoagulation management. Available data suggest that these are credible models for a significant minority of patients if underpinned by structured training and follow-up. The guidelines presented are necessarily consensual and outline procedures for patient selection, training, product procurement, product maintenance, quality assurance procedures, dosage adjustment and clinical supervision. The cost-effectiveness of these models remains to be elucidated within the UK. Further data on both health economic and clinical outcomes are required from UK based studies before widespread implementation of self-testing and management can be recommended on a wider scale.

Anticoagulants↗
PubMed1995

Achieving credibility in risk assessment models.

Validation of a mathematical model requires demonstrating that a model is free of mathematical errors (internal consistency), is sensitive to large but not small errors or uncertainties in parameter values (verifiability and robustness), reproduces experimental observations on the system being modeled (external consistency), and leads to testable predictions of the system's biological properties. To be heuristically valid, a model also must be a realistic representation of the actual biological system. Only then would the model's predictions be credible to the wider community of biological scientists who would use the model for risk assessment and dose or species extrapolation. Owing to incomplete data, most current dosimetric models are insufficiently realistic to pass this test of credibility. Enhancements to such models that would help achieve credibility are presented, and suggestions are offered for institutionalizing realistic modeling practices in risk assessment.

Animals↗
PubMed1983

Hyperacute pulmonary vasculitis in rabbits receiving prolonged infusions of activated complement. A possible model for triggering events in adult respiratory distress syndrome.

We have postulated a role for activated plasma complement and for stimulated granulocytes in the triggering events of the adult respiratory distress syndrome (ARDS). Because brief periods of complement activation have proved to be pale mimics of the clinical syndrome, we extended our earlier models by infusing potently activated plasma complement into rabbits over a prolonged period of time (3 h). The expected leukostasis occurred, but pulmonary dysfunction remained modest. Nonetheless, piecemeal microvascular necrosis did develop, rendering this current model more credible than former models as a mimic of triggering events in ARDS; longer-term follow-up of such animals will be necessary to determine if this is indeed the case. Perhaps of even greater interest, the neutrophilic leukostasis was observed to progress over the 3 h to a predominantly lymphocytic leukostasis, a dramatically more rapid progression than is typical of such immune complex diseases as serum sickness and the Arthus reaction; further studies are in progress to elucidate the mechanism of this lymphostasis.

Acute Disease↗
PubMed2000

A meta-analysis of the interrelationships between the modes in Roy's adaptation model.

A meta-analysis of nine empirical studies based on Roy's adaptation model was conducted to determine the magnitudes of the interrelationships of the four modes: physiological, self-concept, role function, and interdependence. Small to medium effect sizes between each two modes do support the proposition of Roy's model that the four modes are interrelated. The only exception is the relationship between interdependence and physiological modes, as shown by the non-significant effect size of .04. The present study also discusses several limitations that should be considered when interpreting the findings of this meta-analysis. This study does provide a useful compilation of the Roy model's credible studies and proposes a direction for further research. The results indicate a need for further study to explore the relationship in all response modes to have a clearer understanding of the credibility of Roy's model.

Adaptation, Psychological↗
PubMed1991

A model for the maximum credible hourly impact on any ground receptor from point sources with thermal plume rise.

A pollutant dispersion model is developed, allowing fast evaluation of the maximum credible 1-h average concentration on any given ground-level receptor, along with the corresponding critical meteorological conditions (wind speed and stability class) for stacks with buoyant plumes in urban or rural areas. Site-specific meteorological data are not required, as the computed concentrations are maximized against all credible combinations of wind speed, stability class, and mixing height. The analysis is based on the dispersion relations of Pasquill-Gifford and Briggs for rural and urban settings, respectively, the buoyancy induced dispersion correlation of Pasquill, the wind profile exponent values suggested by Irwin, the buoyant plume rise relations of Briggs, as well as the Benkley and Schulman's model for the minimum mixing heights. The model is particularly suited for air pollution management studies, as it allows fast screening of the maximum impact on any selected receptor and evaluation of the ways to have this impact reduced. It is also suited for regulatory purposes, as it can be used to define the minimum stack size requirements for a given source as a function of the exit gas volume and temperature, the pollutant emission rates and their hourly concentration standards, as well as the source location relative to sensitive receptors.

Journal Article↗
PubMedDate not supplied

Validation of health economic models: the example of EVITA.

OBJECTIVES: The credibility of models rests on their validity. An age-structured decision analytic model, Economic Varicella Vaccination Tool for Analysis (EVITA), has been developed to examine the epidemiologic and economic effects of universal varicella (chicken pox) vaccination in Germany. EVITA combines a varicella transmission module describing the spread of infection in a population over time with a second module describing the course of disease in case of an infection. Any vaccination strategy can be assessed dependent on coverage levels and targeted age group. Model input data include epidemiologic, clinical, and economic information, which were mainly derived from actual varicella cases (retrospective survey). The objective of this study was to illustrate the efforts undertaken to validate the EVITA model. METHODS: We assess the descriptive validity, i.e., whether the model provides an adequate picture of the reality and covers all relevant aspects of the spread of varicella and the course of disease. Analyzing the consistency of the model results with observable data does technical verification. Face validity, i.e., the consistency with the underlying theoretical basis of the spread of varicella, is analyzed with respect to results on possible age shifts and elimination of varicella. Tests of corroboration, or convergent validity, are performed by comparisons with other models. RESULTS: Without vaccination, the EVITA model predicts undiscounted, indirect costs of 154 million euros, nearly 40,000 complications and 5,700 hospitalizations per year owing to varicella. These results, especially the distribution of complications and hospitalizations, fit well with population-based survey data. The development of the EVITA model is based on an established epidemiologic model and on real-life data from the survey, ensuring descriptive validity. Results on age shifts and elimination show face validity. Although other models differ considerably with respect to methods applied, the economic results of EVITA, i.e., a benefit-cost ratio of 4.12 when vaccinating young children, lies in the range found in other studies. This underscores its convergent validity. Comparable with other studies, discount rates and price of vaccine proved to be most sensitive variables. CONCLUSIONS: EVITA provides a powerful tool to simulate the highly complex processes associated with varicella infections and the impact of vaccination. The results of EVITA provide a reliable tool for informed decision making and should enhance the acceptance of such models.

Adolescent↗
PubMed2004

Cigarette smoking among school teachers in Tobago.

Tobago, until lately, was considered a society with a low prevalence of cigarette smoking. Recent surveys, however, showed an increasing smoking prevalence among school children. To assess whether teachers in Tobago can be credible role models for their pupils, we carried out a cross-sectional survey on their smoking-related attitudes and behaviour in 2002. We distributed anonymous, structured questionnaires to teachers of all 52 primary and secondary schools in the island and conducted structured observations in schools. Of 579 teachers present during the survey, 559 (97%) returned a completed questionnaire; 8.6% of the male and 2.4% of the female teachers reported to be current cigarette smokers; slightly higher proportions had ever been daily smokers. Teachers were well aware of the harmful effects of smoking. Significantly more non-smokers than current smokers were in favour of strict school smoking regulations. The vast majority of the teachers perceived anti-smoking education as their duty. None of the schools had dedicated smoking rooms for teachers, and we found no cigarette butts in or around teachers' rooms. In Tobago, teachers have a lower reported prevalence of cigarette smoking than their pupils. Thus, most teachers can be credible role models with regard to smoking prevention and should be encouraged to become more active in school-based preventive activities.

Adolescent↗
PubMedDate not supplied

Carcinogenic effects of low-level ionizing radiation: problems and prospects.

For public health purposes, the overall risks of cancer are assumed to increase in proportion to the dose of ionizing radiation, without a threshold. Assessment of the risks that may be attributable to doses below the range in which empirical data are available, however, entails the use of models, the credibility of which depends on the extent to which the models are consistent with what is known about the occurrence and mechanisms of the effects in question. Although the weight of existing evidence is consistent with the hypothesis that the risks of genetic and carcinogenic effects of ionizing radiation increase as linear-nonthreshold functions of the dose, this concept is challenged by some observers in view of growing evidence that low doses of radiation may elicit adaptive responses that enhance the repair of DNA damage and protect in other ways as well. Further research is needed to resolve the issue.

Adaptation, Physiological↗
PubMed1986

Tobacco demarketing campaigns and role model selection in developing countries: the case of Bangladesh.

Tobacco production and consumption is on the increase in developing countries. It is imperative that effective demarketing of tobacco products be initiated. This will call for effective and credible role models. A major study conducted in Dhaka, Bangladesh indicates that doctors are the most credible source of information concerning the dangers of tobacco consumption. Campaigns utilizing elderly male doctors as role models are called for in working to correct to problem of tobacco used in developing countries.

Attitude to Health↗
PubMedDate not supplied

Incorporating direct and indirect evidence using bayesian methods: an applied case study in ovarian cancer.

OBJECTIVE: To demonstrate the application of a Bayesian mixed treatment comparison (MTC) model to synthesize data from clinical trials to inform decisions based on all relevant evidence. METHODS: The value of an MTC model is demonstrated using a probabilistic decision-analytic model developed to assess the cost-effectiveness of second-line chemotherapy in ovarian cancer. Three clinical trials were found that each made a different pair-wise comparison of three treatments of interest in the overall patient population. As no common comparator existed between the three trials, an MTC model was used to assess the combined weight of evidence on survival from all three trials simultaneously. This analysis was compared to an alternative approach that combined two of the trials to make the same comparison of all three treatments using a common comparator, and an informal approach that did not synthesize the available evidence. RESULTS: By including all three trials using an MTC model, the credible intervals around estimated overall survival were reduced compared with making the same comparison using only two trials and a common comparator. Nevertheless, the survival estimates from the MTC model result in greater uncertainty around the optimal treatment strategy at a cost-effectiveness threshold of 30,000 pounds per quality-adjusted life-year. CONCLUSIONS: MTC models can be used to combine more data than would typically be included in a traditional meta-analysis that relies on a common comparator. They can formally quantify the combined uncertainty from all available evidence, and can be conducted using the same analytical approaches as standard meta-analyses.

Antineoplastic Agents↗
PubMed2004

Forecasting clinical disease in pigs: comparing a naive and a Bayesian approach.

In veterinary practice the clinician often evaluates and predicts herd health status over time according to clinical criteria. In this paper, we modeled three different clinical signs among pigs based on longitudinal clinical observations in 15 pig herds. We compared and discussed the outputs from two different approaches for making clinical forecasts in a herd: a naive approach using a simple time series model with previous disease observations as predictors and a Bayesian state space models approach, in which the time lag variable entered into the random component of the model. We used the Markov chain Monte Carlo technique to calculate posterior distributions of the forecasts. For the herd specific forecasts the results showed that there were only minor differences between the forecasts from the simple time series model and the median forecasts from the Bayesian model. However, the credibility intervals from the Bayesian model were wider than the forecasts from the simple model and, therefore the Bayesian model encompassed the variability in the forecasts better. Compared to the statistical model, the simple time series would be easier to implement in a practical setting. However, the latter lacks the inherent "generality" from the statistical model that allows the user to make statements about the distribution of the herds and to predict disease status based on the "average" correlation among the herds. The applicability of the Bayesian approach within a clinical decision-making framework was discussed, with special emphasis on the use of prior information and clinical forecasting.

Animals↗
PubMed1989

The Foster Care Research Project: clinical impressions.

A two-year prospective study compared individual and group models of support for foster parents. Results showed greater foster parent satisfaction with the group model. An independent critique identified methodological flaws that would preclude further differentiation of the models and suggested that clinical impressions and trends in favor of the group model be given credibility. Operation of the group model is described, and reasons for the differences between clinical and experimental findings are discussed.

Adolescent↗
PubMed2006

On allosteric control model of bone turnover cycle containing osteocyte regulation loop.

One approach to developing a mathematical model that predicts osteoactivity both in bio-scaffolds, as well as the in bone tissue in vivo, is based on a bio-cybernetic vision of basic multicellular unit (BMU) action. In the case of the model presented in this paper, some of the loops of regulation have been modified to reflect the range of allosteric control mechanisms: Michaelis-Menten, Hill, Adair, Koshland-Nemethy-Filmer (KNF), Monod-Wyman-Changeux (MWC). This approach has resulted in a four-dimensional system that shows steady cyclic behaviour using a range of constants with clear biological meaning. The initial findings suggesting that a steady state appears as a cycle in multidimensional phase space and this is discussed in this paper. The existence of this cycle in the osteoclasts-osteoblasts-osteocytes-bone subspace indicates that there is a conservative value along steady trajectories for this dynamic system. Biophysical interpretation of this conservative value has been proposed as a kind of substrate-energy regenerative potential of the bone remodelling system with a similarity to the classical physical value-energy. Such a recovery "potential" is directed against both mechanical and biomechanical damage to the bone. The current model has credibility when compared to the normal bone remodelling process. In the framework of widely recognised Michaelis-Menten mechanisms of allosteric regulation the cyclic attractor, described formerly for a pure cellular model, prevails for different forms of feedback control. This finding demonstrates the viability of the suggestion of the subsistence of conservative value (analogous to energy) that characterises the recovery potential of the bone remodelling cycle. The results indicate that the robust behaviour of the model is maintained from the simple cellular level to the molecular biochemical level of regulation.

Allosteric Site↗
PubMed2006

'Participate to learn': a promising practice for community ABI rehabilitation.

OBJECTIVE: To identify best practices and promising practices to enhance participation in meaningful and productive activities. METHOD: An electronic search of the ABI rehabilitation research literature since 1990 yielded 974 articles of which 30 focused on interventions that targeted participation and evaluated effectiveness using direct measures of participation. Three reviewers rated these articles according to the standards set out by the Centre for Reviews and Dissemination. Following the systematic review, an interpretive review of the same articles was completed. RESULTS: Only three studies were rated as strong. No best practices were identified. Three promising practices found some support. The interpretive review suggested 'Participate to learn' as a useful rehabilitation model. The model rests on roles as goals, learning by experience in real-life contexts and the use of personal and environmental support to enable participation. CONCLUSIONS: 'Participate to learn' is both a credible rehabilitation model and deserving of more study.

Brain Injuries↗
PubMed1994

ARRIVE: an AIDS education/relapse prevention model for high-risk parolees.

An AIDS prevention training program for parolees recently released from prison with histories of drug injection was developed and evaluated. Key program elements included: a social learning approach to prevention which emphasized resistance skills training; a self-help orientation stressing individual responsibility; therapeutic community principles such as credible role models and community building; and job readiness training for the AIDS prevention/outreach field. A total of 394 eligible parolees (81% male, 19% female) were recruited, of whom 241 attended the program, including 164 completers. One year follow-up results showed that ARRIVE participation significantly decreased certain sexual and drug-related risk behaviors and improved parolees' community adjustment.

AIDS Serodiagnosis↗
PubMed2006

Blinding protocols, treatment credibility, and expectancy: methodologic issues in clinical trials of osteopathic manipulative treatment.

CONTEXT: In testing an experimental new drug or therapy, the gold standard in biomedical research for determining treatment efficacy is the randomized controlled trial (RCT). In pharmaceutical trials, inert placebos are an easily administered control that facilitates blinded comparisons. In clinical trials that study the effects of manual interventions, researchers must carefully consider their use of treatment control models. Choosing credible controls that will minimize bias in osteopathic manipulative treatment (OMT) clinical trials poses unique challenges to researchers because of heterogeneous OMT methods and practice. OBJECTIVE: To compare the treatment credibility of sham manipulative treatment and untreated controls to active OMT. METHODS: Subjects recruited for an OMT clinical trial for chronic low back pain completed a treatment-credibility rating scale comparing two written descriptions of the study interventions offered. The scale was administered to subjects before trial entry and at 6-month follow-up. Scale scores were used to compute credibility ratios for both intervention protocols (ie, OMT vs sham manipulative treatment). Repeated measures analysis of variance was used to assess changes in the credibility ratio over time, including the measurement of study group and time main effects, as well as study group x time interaction effects. RESULTS: Subjects (N=91) perceived OMT as a more credible therapeutic option than sham manipulative treatment both at trial entry and at 6-month follow-up (P<.05). Among subjects completing the study protocol (n=66), there were no changes in perceived credibility of the study interventions over time. There were no significant differences in the credibility ratio among study groups (P=.64) or over time (P=.79). In addition, there were no significant study group x time interactions (P=.59). CONCLUSIONS: In clinical trials, OMT may be perceived by subjects as a more credible treatment alternative than many control procedures. Treatment credibility can interact with subject expectations and study design in complex ways. When analyzing the treatment effects of OMT, investigators must consider the effects of these two subjective elements when competing interventions are offered and subjects are asked to self-report data. Study design should be optimized to equalize these effects among interventions.

Evidence-Based Medicine↗
PubMed1993

A modeling approach to hospital location for effective marketing.

This paper develops a mixed integer linear programming model for locating health care facilities. The parameters of the objective function of this model are based on factor rating analysis and grid method. Subjective and objective factors representative of the real life situations are incorporated into the model in a unique way permitting a trade-off analysis of certain factors pertinent to the location of hospitals. This results in a unified approach and a single model whose credibility is further enhanced by inclusion of geographical and demographical factors.

Algorithms↗