Influence Of Model Variables Research Articles

New Empirical Strategies for the Study of Parliamentary Government Formation

In recent years, a consensus has developed that the conditional logit (CL) model is the most appropriate strategy for modeling government choice. In this paper, we reconsider this approach and make three methodological contributions. First, we employ a mixed logit with random coefficients that allows us to take account of unobserved heterogeneity in the government formation process and relax the independence of irrelevant alternatives (IIA) assumption. Second, we demonstrate that the procedure used in the literature to test the IIA assumption is biased against finding IIA violations. An improved testing procedure reveals clear evidence of IIA violations, indicating that the CL model is inappropriate. Third, we move beyond simply presenting the sign and significance of model coefficients, suggesting various strategies for interpreting the substantive influence of variables in models of government choice.

Application of genetic algorithm for modeling of dense packing of concrete aggregates

Sequential Packing Algorithm (SPA) was developed to model the dense packing of large assemblies of particulate materials (in the order of millions). These assemblies represent the real aggregate systems of portland cement or asphalt concrete. To improve the SPA performance, the program engine was updated with a genetic algorithm (GA) search module. Multi-cell packing procedures, fine adjustment of the algorithm’s parameters, as well as implementation of GA were effective tools to optimize the computational resources, to speed-up the SPA and to pack very large volumes of spherical entities. The developed algorithm generates and visualizes dense packings corresponding to concrete aggregates. The influence of model variables on the degree of packing and the corresponding distribution of particles was analyzed. Based on the simulation results, different particle size distributions of particulate materials are correlated to their packing degree. These packings agreed well with the standard requirements and available research data. The results of the research can be applied to the optimal proportioning of concrete mixtures.

Optimization of a Computer Simulation Model for Packing of Concrete Aggregates

A simulation algorithm was developed for modeling the dense packing of large assemblies of particulate materials (in the order of millions). These assemblies represent the real aggregate systems of portland cement concrete. Two variations of the algorithm are proposed: sequential packing model and particle suspension model. A developed multicell packing procedure as well as fine adjustment of the algorithm's parameters were useful to optimize the computational resources (i.e., to realize the trade-off between the memory and packing time). Some options to speed up the algorithm and to pack very large volumes of spherical entities (up to 10 million) are discussed. The described procedure resulted in a quick method for packing of large assemblies of particulate materials. The influence of model variables on the degree of packing and the corresponding distribution of particles was analyzed. Based on the simulation results, different particle size distributions of particulate materials are correlated to their packing degree. The developed algorithm generates and visualizes dense packings corresponding to concrete aggregates. These packings show a good agreement with the standard requirements and available research data. The results of the research can be applied to the optimal proportioning of concrete mixtures.

Cost effectiveness of ramipril in patients with non-diabetic nephropathy and hypertension: economic evaluation of Ramipril Efficacy in Nephropathy (REIN) Study for Germany from the perspective of statutory health insurance.

In the Ramipril Efficacy In Nephropathy (REIN) trial, ramipril significantly lowered the rate of reaching the combined end-point of doubling of baseline serum creatinine levels or end-stage renal failure (ESRF). To determine the additional cost per patient-year of chronic (long term) dialysis avoided (PYCDA) when the ACE inhibitor, ramipril, was added to conventional treatment of patients with non-diabetic nephropathy and hypertension. Statutory Health Insurance (SHI) provider in Germany. Data from the REIN Study were used in a cost-effectiveness analysis (CEA). A modelling approach was used, which was based on secondary analysis of published data, and costs were those incurred by the SHI provider (i.e. SHI expenses). In the base-case analysis, average case-related SHI expenses were applied and PYCDA were quantified using the cumulative incidence of ESRF as observed in the REIN trial. The incremental cost-effectiveness ratios (ICERs) of ramipril varied between about -76,700 deutschmarks (DM) and -DM81,900 per PYCDA (DM 1 approximately equals 0.55 US dollars; 1999 values), according to the treatment periods of 1 year and 3 years, respectively. In the sensitivity,analysis, the robustness of the model and its results were shown when the extent of influence of different model variables on the base-case results was investigated. First, probabilities of ESRF and PYCDA were estimated according to the Weibull method. Second, the influence of the model variables on the target variable was quantified using a deterministic model. Third, the dependency of the target variable (ICER) on random variables was described in a simulation. The cost for chronic dialysis had by far the greatest impact on the target variable, which was 28 times greater than the impact of clinical effectiveness of ramipril, i.e. the number of PYCDA. There were net savings per PYCDA with ramipril treatment after 1, 2 and 3 years: 95% of the 10,000 simulation steps resulted in savings of between DM69 500 and D94,600 per PYCDA after 3 years. Results from this evaluation show that ramipril offers enormous savings from the perspective of the SHI provider (third-party payer) in Germany when added to the conventional treatment of patients with non-diabetic nephropathy and hypertension.

Cost-effectiveness analysis of ramipril in heart failure after myocardial infarction. Economic evaluation of the Acute Infarction Ramipril Efficacy (AIRE) study for Germany from the perspective of Statutory Health Insurance.

Data from the Acute Infarction Ramipril Efficacy (AIRE) study were used in a cost-effectiveness analysis to determine the incremental cost per life-year gained (LYG) when the ACE inhibitor ramipril was added to conventional treatment in patients with heart failure after acute myocardial infarction. In the AIRE trial, the addition of ramipril significantly lowered rates of total mortality and rehospitalisation due to heart failure. The cost-effectiveness analysis was conducted from the perspective of the Statutory Health Insurance (SHI) provider in Germany. A modelling approach was used which was based on secondary analysis of existing data, and costs were those incurred by SHI (i.e. expenses of SHI). In the base-case analysis, average case-related expenses of SHI were applied and LYG were quantified by the method of Kaplan and Meier. The incremental cost-effectiveness ratios of ramipril varied between 2500 and 8300 deutschmarks (DM) per LYG (1993 values for inpatient and 1995 values for outpatient treatment; DM1 approximately $US0.70), according to the treatment periods of 3.8 years and 1 year, respectively. In the sensitivity analysis, the robustness of the model and its results was shown when the extent of influence of different model variables on the base-case results was investigated. First, survival probability and LYG were estimated according to the Weibull method. Second, the dependency of the target variable (i.e. incremental cost per LYG) on random variables was described in a simulation. Third, the influence of the model variables on the target variable was quantified using a deterministic model. The variance of the target variable was broad and the hospitalisation impact of adding ramipril to conventional treatment was an independent variable with much greater influence on the target variable than the parameter of clinical effectiveness, i.e. the number of LYG. Results of this evaluation showed that ramipril has a favourable incremental cost-effectiveness ratio for the treatment of heart failure in post myocardial infarction patients and can be considered an economical therapeutic agent from the perspective of SHI (third-party payer) in Germany.