Search

This chapter illustrates computer simulation “model thinking,” with brief descriptions of five recent health models along an abstract to applied spectrum. The author starts with a very simple model to assess not only the cross-sectional but also the lifetime redistributive impact of Canada’s publicly funded healthcare. Next is a multilevel interacting agent model seeking to understand why the correlations between city-level income inequality and mortality are so different between Canada and the United States. Following are models that significantly generalize the concept of attributable fraction applied to health-adjusted life expectancy and a genetic missing model to support cost-effectiveness of risk-based breast cancer screening policy options. The fifth model is the most detailed and is being applied to develop projections of long-term care utilization and costs. While this is a diverse set of models, collectively, they illustrate the range of possibilities, and the benefits of “model thinking.”

We present a detailed and accurate physics based method for modeling flash memory programming characteristics when the substrate contains different percentages of Germanium. Typical memory cells are programmed by moving electrons from the substrate to the floating gate. We determine this electron movement by considering the contributions attributed to the Nonquasi-Static gate current and tunneling currents while keeping the Germanium percentage as an independent variable. The simulations accuracy is further increased by using Nonquasi-Static methods to determine the drain and source currents as well as the device capacitance values. The goal of this paper is to highlight the physical parameters of the memory cell that are affected by Germanium and show the improvements that can be achieved by using Silicon-Germanium (SiGe) substrate material versus Silicon only. Several papers have been published on MOSFET's with SiGe substrates but none have been published on the use of SiGe substrates to improve flash memory programming.

We present a detailed and accurate physics based transient simulation for modeling flash memory programming characteristics using nonquasi-static and tunneling equations versus the typical Lucky-Electron Model. The result is a set of simple expressions that were originally developed for a MOSFET and adapted for use in floating gate memory. Of greater importance is the extensive use of physical parameters as opposed to the scale factors and probabilities used in other models. This technique allows floating gate memory designers to determine the nominal programming characteristics of single-level and multi-level memory cells prior to the fabrication process. This technique also allows designers to determine the effects of fabrication tolerances on the performance of the memory cell. The accuracy of this model was validated through comparison with experimental data and simulation results presented in several publications.

Background:The majority of children with chronic neurodevelopmental disabilities are surviving to adulthood. Our goal was to assess how prepared and comfortable adult neurologists are in treating young adults with childhood onset chronic neurological conditions and evaluate the difficulty pediatric neurologists experience when transferring these patients to adult care.Methods:We conducted a cross-sectional study using two postal surveys of all pediatric and adult neurologists in the province of Quebec, Canada.Results:The response rate was 51.5%, with 119 neurologists completing the survey. Half of neurologists agreed that adult neurologists may not have adequate training in childhood onset disorders to prepare them to manage the disorders in adulthood, and 60% of pediatric neurologists reported having difficulty finding an adult provider for their patients. Adult neurologists were least comfortable treating patients with autism, chromosomal or metabolic disorders, and cognitive or behavioral disorders.Conclusion:Almost half of those surveyed believed that adult neurologists are not adequately trained to care for this growing patient population. Improving treatment comfort and knowledge among adult neurologists in childhood onset chronic neurological conditions may smooth the transition of these young adults from pediatric to adult care.

We present a detailed and accurate physics-based transient simulation for modeling Flash memory erase characteristics when the substrate contains different percentages of germanium (Ge). Typical cells are erased by moving electrons from the floating gate to the drain, source, or substrate. This paper addresses substrate erase modeling using a simulation based on the solution to Poisson's equation with Ge percentage as an independent variable. The goal of this paper is to demonstrate the derivation of an accurate erase simulation and show the improvements that can be achieved by using silicon-germanium (SiGe) substrate material versus silicon (Si) only. Several papers have been published on MOSFETs with SiGe substrates, but none has been published on the use of SiGe substrates in Flash memory.

We present a detailed and accurate physics based transient simulation for modeling flash memory erasing. Typical cells are erased by moving electrons from the floating gate to the drain, source or substrate. This paper addresses substrate erasing using a negative gate bias voltage based on the approximate solution to Poisson's equation. Substrate erasing using a negative gate bias voltage is one of the more prevalent ways to erase flash memory in currently available consumer products. Many papers have been published on this topic but rarely present detailed derivations and none using this exact set of equations to model this erasing process.

The National Lung Screening Trial (NLST) demonstrated that low-dose computed tomography (LDCT) screening reduces lung cancer mortality in a high-risk U.S. population. A microsimulation model of LDCT screening was developed to estimate the impact of introducing population-based screening in Canada.LDCT screening was simulated using the lung cancer module of the Cancer Risk Management Model (CRMM-LC), which generates large, representative samples of the Canadian population from which a cohort with characteristics similar to NLST participants was selected. Screening parameters were estimated for stage shift, LDCT sensitivity and specificity, lead time, and survival to fit to NLST incidence and mortality results. The estimation process was a step-wise directed search.Simulated mortality reduction from LDCT screening was 23% in the CRMM-LC, compared with 20% in the NLST. The difference in the number of lung cancer cases over six years varied by, at most, 2.3% in the screen arm. The difference in cumulative incidence at six years was less than 2% in both screen and control arms. The estimated percentage over-diagnosed was 24.8%, which was 6% higher than NLST results.Simulated screening reproduces NLST results. The CRMM-LC can evaluate a variety of population-based screening strategies. Sensitivity analyses are recommended to provide a range of projections to reflect model uncertainty.

As the population ages and the prevalence of comorbid conditions increases, the need for feasible, validated methods of comorbidity surveillance in chronic diseases such as multiple sclerosis (MS) increases.Using kappa (k) statistics, we evaluated the performance of administrative case definitions for comorbidities commonly observed in MS by comparing agreement between Manitoba (MB) administrative data and self-report (n = 606) and Nova Scotia (NS) administrative data and self-report (n = 1923).Agreement between the administrative definitions and self-report was substantial for hypertension (k = 0.69 [NS], 0.76 [MB]) and diabetes (k = 0.70 [NS], 0.66 [MB]); moderate for hyperlipidemia (k = 0.53 [NS], 0.51 [MB]) and heart disease (k = 0.42 [NS], 0.51 [MB]) and fair for anxiety (k = 0.27 [NS], 0.26 [MB]). In NS, agreement was substantial for inflammatory bowel disease (k = 0.71) and moderate for epilepsy (k = 0.48).Administrative definitions for commonly observed comorbidities in MS performed well in 2 distinct jurisdictions. This suggests that they could be used more broadly across Canada and in national studies.Performance des définitions administratives de cas pour les affections concomitantes de la sclérose en plaques au Manitoba et en Nouvelle-Écosse.Au fur et à mesure du vieillissement de la population et de l’augmentation de la prévalence d’affections concomitantes, le recours à des méthodes fiables et efficaces de surveillance des affections concomitantes de maladies chroniques telles que la sclérose en plaques (SP) s’avère de plus en plus nécessaire.Nous avons évalué, au moyen de la statistique kappa (k), la performance des définitions administratives de cas pour les affections concomitantes fréquemment observées en lien avec la SP en comparant les concordances entre les données administratives et les données provenant d’autodéclarations au Manitoba (MB) (n = 606) et en Nouvelle-Écosse (NS) (n = 1 923).Les concordances entre les définitions administratives et les autodéclarations étaient bonnes pour l’hypertension (k = 0,69 [NS] et 0,76 [MB]) et le diabète (k = 0,70 [NS] et 0,66 [MB]), modérées pour l’hyperlipidémie (k = 0,53 [NS] et 0,51 [MB]) et la cardiopathie (k = 0,42 [NS] et 0,51 [MB]) et médiocres pour l’anxiété (k = 0,27 [NS] et 0,26 [MB]). La concordance était bonne en Nouvelle-Écosse pour la maladie inflammatoire chronique de l’intestin (k = 0,71) et modérée pour l’épilepsie (k = 0,48).Les définitions administratives étaient performantes dans les deux provinces pour plusieurs affections concomitantes fréquemment observées en lien avec la SP. À la lumière de ces résultats, il semble que ces définitions puissent être utilisées plus largement au Canada et dans les études nationales.

In an era of increasingly complex medical care and escalating costs, healthcare decision-makers often rely on a broad range of indicators to gauge the health of a population, the quality of hospital care and the performance of healthcare systems. Reports that rank the health of Canadians and Canada's healthcare systems according to these indicators are widely cited in the media. These reports attempt to condense a complicated array of statistics into a relatively simple number, a rank that is used to make international and provincial comparisons. These reports have often been inconsistent. Unlike a familiar economic indicator - the gross domestic product (GDP), which represents a complex entity with a single number calculated according to an internationally agreed-upon methodology - rankings of health and healthcare are not yet standardized or well understood. This article aims to improve readers' understanding of ranking reports. It outlines the components and processes that underlie health rankings and explores why such rankings can be difficult to interpret.

We present a detailed and accurate physics based transient simulation for modeling flash memory erasing at ambient and non-ambient temperatures. Typical cells are erased by moving electrons from the floating gate to the drain, source or substrate. Part 1 of this paper derives the equations used to model substrate erasing. This paper addresses drain erase modeling using a simulation based on the solution to Poisson's equation with temperature as an independent variable. The goal of this paper is to demonstrate the derivation of an accurate erase simulation and show the effects of temperature on the threshold voltage during the erase process. Several papers have been published on this topic but fail to present detailed derivations and none using this exact set of equations to model the temperature dependent erasing process.

Health-adjusted life expectancy is a summary measure of population health that combines mortality and morbidity data into a single index. This article profiles differences in health-adjusted life expectancy across income categories for a representative sample of the Canadian population.Mortality data were obtained from the 1991-2001 Canadian census mortality follow-up study, which linked a 15% sample of the 1991 adult non-institutional population with 11 years of death records from the Canadian Mortality Data Base. Information on morbidity was obtained from the Health Utilities Index Mark 3 instrument on the 2000/2001 Canadian Community Health Survey. The Sullivan method was used to compute health-adjusted life expectancy for national deciles of population ranked by income.For both sexes, and with few exceptions, a nearly linear gradient across income deciles emerged for health-adjusted life expectancy at age 25. Compared with people in higher-income deciles, those in lower-income deciles had fewer years of health-adjusted life expectancy. These disparities were substantially larger than those revealed by life expectancy alone.These findings highlight the generally worse health-related quality of life of lower-income groups. The results demonstrate that assessments of socio-economic disparities in health should include the effects of both mortality and morbidity.

To systematically review the published evidence for a relationship between human herpes virus 6 (HHV-6) and multiple sclerosis (MS).The medical literature was searched using MEDLINE and the Cochrane database. Retrieved studies are presented according to the experimental technique(s) used. The studies are rated for quality using a priori defined criteria.Twenty-eight studies were retrieved. A total of 12 different experimental techniques were used. Four of these techniques provided evidence for a relationship between HHV-6 and MS, but none were able to show a causative relationship.The available literature provides some support for a relationship between HHV-6 and MS. The limitations of the available studies and directions for future research are discussed.

We have evaluated the epidemiological evidence for an aetiological role of varicella zoster virus (VZV) infection in the development of multiple sclerosis (MS). A MEDLINE search of the English language literature for 1965–99 identified 40 studies. These studies were categorized as seroepidemiological (13), case-control (23), historical cohort (2) or ecological (2). One study used both case-control and historical cohort methodologies. Studies were then classified according to methodological rigour, using criteria derived from published guidelines for the epidemiological study of MS. There was a large variability in the quality of evidence. The five studies with the best methodology failed to show an increased risk of MS associated with varicella or zoster infections. At the present time there is insufficient evidence to support an important aetiological role of VZV infection in the development of MS.

To develop and assess the consistency and validity of simple cognitive function measures for an elderly population with low levels of formal education for use in a longitudinal study of dementia.Data were from the population longitudinal study 'Growing old in Leganés' (Spain). In 1993, a random sample of 1540 people over 65 was drawn from the City Roll of Leganés from which 1284 (83%) were successfully interviewed. Measures of memory and orientation were based on the SPMSQ (Short Portable Mental Status Questionnaire), the Barcelona test and the short story from EPESE (Established Populations Epidemiologic Studies of the Elderly). Non-response to a test item was coded as an error. Internal consistency was assessed by factor analysis and Cronbach's alpha. Construct validity was examined with multiple linear regressions of the proposed measurements on variables chosen from the existing literature on cognitive function.Two factors, memory and orientation, emerged from the factor analysis. Internal consistency of the proposed indexes for memory and orientation was acceptable. Memory and orientation scores were summed into one summary index of cognition. Associations between covariates and both cognitive indexes were in the expected direction. Among those highly functional, orientation was influenced by illiteracy due to higher error rates in the time orientation items based on dates; however, memory and summary scores were not significantly different by literacy status. A large proportion of the variance in IADL was explained by the memory and orientation measures.The memory and orientation indexes are valid and reliable measurements of cognitive function for use in a population of community dwelling elderly with low levels of formal education and high rates of illiteracy.

Because lung cancer is a major health care problem in Canada, it would be useful to identify the direct health care costs of diagnosing and treating this disease and to create an analytic framework within which diagnostic and therapeutic options can be assessed. This paper describes a method of modelling the costs of care for lung cancer. The perspective of the costing model is that of the government as payer in a universal health care system. Clinical algorithms were developed to describe the management of non-small cell (NSCLC) and small cell (SCLC) lung cancer. Patients were allocated to the treatment algorithms in the model, based on a knowledge of the stage distribution of cases within provincial cancer registries and an estimate of the use of therapeutic modalities, according to lung cancer experts. A microsimulation model (POHEM) developed at Statistics Canada was used to integrate data on risk factors, disease onset and progression, health care resource utilization and direct medical care costs. The model incorporates survival data on patients, according to cell type and stage, based on published studies. Relapse and terminal care costs were assigned during the year of death, in order to determine the cost of continuing care and the cumulative cost of lung cancer management over time. Patients surviving five years were assumed to be cured. The model estimates that the total five year cost to provide care to the 15,624 cases of lung cancer diagnosed in Canada in 1988 was in excess of $328 million. Over 82% of this total was spent in the first year for diagnostic tests, therapy (surgery, chemotherapy, radiation therapy, or combinations of these), hospitalization and follow-up costs. The average five year cost per case was $21,000, and ranged from a high of $29,860 for limited disease SCLC, to a low of $16,500 for Stage IV NSCLC. The actual cost of providing care, including the management of complications, is unknown and our estimates should be regarded as an idealized estimate of the cost of lung cancer management. However, the POHEM model has a level of sophistication which, we believe, reasonably reflects the cost per case and total costs of treating lung cancer by stage and therapeutic modality in Canada.

The POpulation HEalth Model (POHEM) lung cancer microsimulation model has provided a useful framework for calculating the cost of managing individual cases of lung cancer in Canada by stage, cell type, and treatment modality, as well as the total economic burden of managing all cases of lung cancer diagnosed in Canada. These data allow an estimation of the overall cost effectiveness of lung cancer therapy. the model also provides a frame-work for evaluating the cost effectiveness of new therapeutic strategies, such as combined modality therapy for stage III disease or new chemotherapy drugs for stage IV disease. By expressing the cost of lung cancer treatment as cost of life-years gained, such analyses allows useful comparisons of the cost effectiveness of these treatments with those of other costly but accepted medical therapies.

A variety of developments have come together to serve as both an impetus to and foundation for the development of a new POpulation HEalth Model (POHEM) at Statistics Canada. Part of the impetus is statistical and derives from weaknesses in Canada's health statistics programme--particularly the lack of balance between information on health outcomes and health care resource consumption, and the absence of a coherent statistical structure. The other major impetus is the need for rational processes for managing and allocating resources to improve the health of Canadians. The foundation for the development of this model has come from the revolution in computing. Dramatic improvements have opened up new methodological opportunities, particularly sophisticated simulation modelling and detailed analyses of large volumes of microdata. POHEM is designed to build on these increasingly powerful methods in order to meet health statistical and policy needs. At this time, POHEM is like a partially-completed building. This article reviews its motivation, the overall architectural plan, and the portion of the structure already completed. A major portion of POHEM is devoted to the explicit modelling of chronic disease processes, using monte carlo microsimulation methods. The article concludes with illustrations of a few recent applications, focusing on the joint patterns of smoking, cholesterol and heart disease, osteoarthritis and lung cancer morbidity. While POHEM has been developed in a Canadian context, work is under way to create a version that can be used in other countries.

A model adjusting for reductions in quality and quantity of life was developed to estimate the population health impact of musculoskeletal diseases.Using arthritis as the prototype, prevalence, mortality, and severity data from a variety of sources were combined to model a hypothetical cohort of 1,000 individuals through life. Quality adjusted life years and population health expectancy were calculated for those with arthritis and compared to the general population.Without adjusting for quality of life, a cohort of 1,000 women and 1,000 men at age 15 years could expect 65,010 and 58,735 life years, respectively. Adjusting for quality of life, women with arthritis could expect 61,719 life years, and men 57,123 life years. The unadjusted population health expectancy was 65.0 for girls and 58.7 for boys (at age 15 years). Adjusting for quality of life, the population health expectancies were 61.7 and 57.1, years for women and men, respectively.Using this model, the typical adult woman with arthritis can expect to lose 3.3 healthy years of life, and a man, 1.6 healthy years of life. Overall, the model provided a general methodology for determining the population health impact of musculoskeletal diseases. In addition, it is hoped that the methodology will stimulate further research into this area, raise awareness about the uses and limitations of currently available data, and provide a useful model for monitoring the impact of interventions.

The authors discuss the dependency burden that is expected to result from demographic aging in Canada. "The estimated size of the burden depends on projections of demographic change, economic growth, and structural aspects of the major age-sensitive public-sector programmes. The burdens are analysed for 2016 and 2036, the period when demographic aging may be expected to have its most adverse impacts on old-age dependency ratios and public-sector programme costs. Contrary to many popularly expressed concerns, demographic aging is not the most important factor in determining future public-sector costs and revenues. Rather, aspects of the design and management of public-sector programmes represent the greatest area of uncertainty."

Contrast venography (CV) is the standard technique for diagnosing deep vein thrombosis (DVT). Newer noninvasive tests have also proven efficacious. However, there is a lack of data on the level of agreement among observers in their interpretation of the results of the various tests. After agreeing on well-defined criteria, three experienced observers assessed, blindly, the results of tests performed over a 4-month period on 117 patients who were suspected clinically of having had a first episode of DVT. The kappa statistic was used to measure the level of agreement beyond chance for CV (69 patients), red blood cell venography (RBCV) (82 patients) and impedance plethysmography (76 patients). The results of CV were assigned to normal, abnormal or inadequate categories, and those of RBCV and IPG to normal, equivocal or abnormal categories. The kappa values for CV, RBCV and IPG ranged from 0.53 to 0.56, 0.42 to 0.56 and 0.90 to 0.91 respectively. Values greater than 0.75 represented excellent agreement beyond chance and those between 0.40 and 0.75 represented fair to good agreement. Excellent kappa values were obtained for IPG because interpretation of the results of this method is entirely objective. Although the values for CV and RBCV showed good to fair agreement, there was a greater degree of observer variation, despite the well-defined criteria, indicating the subjectivity of interpretation of these test results. It is concluded that the kappa statistic can be used to measure observer variation of the results of tests for diagnosing DVT and may serve as a quality control tool for studies in which more than one person interprets the results.

There is an urgent need for individualized outcome estimates in multiple sclerosis (MS). This is a prerequisite for selecting appropriate therapies in a disease the outcome of which may vary between malignant and benign forms. This question was addressed by using probabilistic mathematical models. The disease course is described by movements of the patient's condition through well-defined disease states. The data used are based upon 278 reports of definite and probable MS cases collected over a 20-year period (1957–1976) at l'Hopital Neurologique de Lyon. A Markov model was first prepared. However, it only provided an overall presentation of the disease which was not very meaningful for the individual patient, and limited studies of potential prognostic variables to dichotomous variables and univariate analyses. A stochastic survival model was then elaborated. It was complex at the theoretical level but in practice, easy to use. Personalized prognosis of a patient could be ascertained by combining several single potential prognostic variables and using their actual value in the case of quantitative variables. Although these models still need to be refined and have to be validated from the present state of the patients and other patient cohorts, they provide for the first time a global description of disease course likelihood and prognosis. The survival model may be adapted to each patient. multiple sclerosis/prognosis/mathematical models