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H. J. W. Mutsaers - One of the best experts on this subject based on the ideXlab platform.

  • The Need for Simple Dynamic Equations to Describe Plant Competition
    Annals of Botany, 1991
    Co-Authors: H. J. W. Mutsaers
    Abstract:

    A dynamic Single-Equation Model for plant interactions is compared with the competition mechanism implicit in larger simulation Models. When light is the limiting factor, both mechanisms can be written in the same mathematical form containing a 'driving force' and a restriction factor. In the Single-Equation Model the driving force is derived directly from the RGR of a competition-free plant. In more comprehensive Models, detailed information on the growth of plant organs has to be generated by subModels (...)

Nicolas Moreau - One of the best experts on this subject based on the ideXlab platform.

  • collective labor supply a Single Equation Model and some evidence from french data
    Journal of Human Resources, 2007
    Co-Authors: Olivier Donni, Nicolas Moreau
    Abstract:

    In Chiappori's (1988) collective Model of labor supply, hours of work are supposed flexible. In many countries, however, male labor supply does not vary much. In that case, the husband's labor supply is no longer informative about the household decision process and individual preferences. To identify structural components of the Model, additional information is needed. We thus consider an approach in which the wife's labor supply is expressed as a function of the household demand for one specific good. We demonstrate that the main properties of Chiappori's initial Model are preserved and apply our results on French data.

  • collective labor supply a Single Equation Model and some evidence from french data
    Post-Print, 2007
    Co-Authors: Nicolas Moreau, Olivier Donni
    Abstract:

    In Chiappori's (1988) collective Model of labor supply hours of work are supposed flexible. In many countries, however, male labor supply does not vary much. In that case, the husband's labor supply is no longer informative about the household decision process and individual preferences. To identify structural components of the Model, additional information is needed. We thus consider an approach in which the wife's labor supply is expressed as a function of the household demand for one specific good. We demonstrate that the main properties of Chiappori's initial Model are preserved and apply our results on French data. (This abstract was borrowed from another version of this item.)

Michael Mcburnett - One of the best experts on this subject based on the ideXlab platform.

  • An Individual-Level MultiEquation Model of Expenditure Effects in Contested House Elections
    American Political Science Review, 1994
    Co-Authors: Christopher Kenny, Michael Mcburnett
    Abstract:

    e shall address questions concerning the impact of candidate spending in congressional elections in a new way. We develop a multiEquation Model of congressional vote choice a v that takes the endogeneity of expenditures into account. We then estimate both this Model and the more traditional Single-Equation Model using individual level survey data. The substantial differences we find between the two Models indicates that the simultaneity bias present in the Single-Equation Model is not trivial. The challenger and incumbent expenditure terms are each significant (whereas only challenger expenditures are in the Single-Equation setup) and of much greater magnitude in the multiEquation case. In addition, we evaluate hypotheses grounded in persuasive communications theory concerning the type of individuals most affected by the messages emanating from the campaigns. We find that individuals with higher education, those with greater interest in campaigns, and those with strongly held convictions are unaffected by candidate spending, whereas individuals lacking each of these attributes are greatly influenced by campaign expenditures.

Ashleigh R Tuite - One of the best experts on this subject based on the ideXlab platform.

  • relatedness of the incidence decay with exponential adjustment idea Model farr s law and sir compartmental difference Equation Models
    Infectious Disease Modelling, 2018
    Co-Authors: Ashleigh R Tuite, Mauricio Santillana, Tahmina Nasserie, Paul E M Fine, David Champredon, Leonid Chindelevitch, Jonathan Dushoff, David N Fisman
    Abstract:

    Abstract Mathematical Models are often regarded as recent innovations in the description and analysis of infectious disease outbreaks and epidemics, but simple mathematical expressions have been in use for projection of epidemic trajectories for more than a century. We recently introduced a Single Equation Model (the incidence decay with exponential adjustment, or IDEA Model) that can be used for short-term epidemiological forecasting. In the mid-19th century, Dr. William Farr made the observation that epidemic events rise and fall in a roughly symmetrical pattern that can be approximated by a bell-shaped curve. He noticed that this time-evolution behavior could be captured by a Single mathematical formula (“Farr's law”) that could be used for epidemic forecasting. We show here that the IDEA Model follows Farr's law, and show that for intuitive assumptions, Farr's Law can be derived from the IDEA Model. Moreover, we show that both mathematical approaches, Farr's Law and the IDEA Model, resemble solutions of a susceptible-infectious-removed (SIR) compartmental differential-Equation Model in an asymptotic limit, where the changes of disease transmission respond to control measures, and not only to the depletion of susceptible individuals. This suggests that the concept of the reproduction number ( R 0 ) was implicitly captured in Farr's (pre-microbial era) work, and also suggests that control of epidemics, whether via behavior change or intervention, is as integral to the natural history of epidemics as is the dynamics of disease transmission.

  • the idea Model a Single Equation approach to the ebola forecasting challenge
    Epidemics, 2016
    Co-Authors: Ashleigh R Tuite, David N Fisman
    Abstract:

    Mathematical Modeling is increasingly accepted as a tool that can inform disease control policy in the face of emerging infectious diseases, such as the 2014-2015 West African Ebola epidemic, but little is known about the relative performance of alternate forecasting approaches. The RAPIDD Ebola Forecasting Challenge (REFC) tested the ability of eight mathematical Models to generate useful forecasts in the face of simulated Ebola outbreaks. We used a simple, phenomenological Single-Equation Model (the "IDEA" Model), which relies only on case counts, in the REFC. Model fits were performed using a maximum likelihood approach. We found that the Model performed reasonably well relative to other more complex approaches, with performance metrics ranked on average 4th or 5th among participating Models. IDEA appeared better suited to long- than short-term forecasts, and could be fit using nothing but reported case counts. Several limitations were identified, including difficulty in identifying epidemic peak (even retrospectively), unrealistically precise confidence intervals, and difficulty interpolating daily case counts when using a Model scaled to epidemic generation time. More realistic confidence intervals were generated when case counts were assumed to follow a negative binomial, rather than Poisson, distribution. Nonetheless, IDEA represents a simple phenomenological Model, easily implemented in widely available software packages that could be used by frontline public health personnel to generate forecasts with accuracy that approximates that which is achieved using more complex methodologies.

  • Projected impact of vaccination timing and dose availability on the course of the 2014 west african ebola epidemic.
    PLOS Currents, 2014
    Co-Authors: David N Fisman, Ashleigh R Tuite
    Abstract:

    The 2014 West African Ebola outbreak has evolved into an epidemic of historical proportions and catastrophic scope. Prior outbreaks have been contained through the use of personal protective equipment, but such an approach has not been rapidly effective in the current epidemic. Several candidate vaccines have been developed against the Ebola virus, and are undergoing initial clinical trials. As removal of population-level susceptibility through vaccination could be a highly impactful control measure for this epidemic, we sought to estimate the number of vaccine doses and timing of vaccine administration required to reduce the epidemic size. Our base Model was fit using the IDEA approach, a Single Equation Model that has been successful to date in describing Ebola growth. We projected the future course of the Ebola epidemic using this Model. Vaccination was assumed to reduce the effective reproductive number. We evaluated the potential impact of vaccination on epidemic trajectory under different assumptions around timing of vaccine availability. Using effective reproductive (Re) number estimates derived from this Model, we estimate that 3-4 million doses of vaccine, if available and administered, could reduce Re to 0.9 in the interval from January-March 2015. Later vaccination would be associated with a progressively diminishing impact on final epidemic size; in particular, vaccination to the same Re at or after the epidemic is projected to peak (April-May 2015) would have little impact on final epidemic size, though more intensive campaigns (e.g., Re reduced to 0.5) could still be effective if initiated by summer 2015. In summary, there is a closing window of opportunity for the use of vaccine as a tool for Ebola epidemic control. Effective vaccination, used before the epidemic peaks, would be projected to prevent tens of thousands of deaths; this does not minimize the ethical challenges that would be associated with wide-scale application of vaccines that have undergone only limited evaluation for safety and efficacy.

Mohamed - One of the best experts on this subject based on the ideXlab platform.

  • Estimation methodology of short-term natural rubber price forecasting Models
    2011
    Co-Authors: Khin, Zainalabidin, Nasir, Chong, Fatimah, Mohamed
    Abstract:

    This study developed a short-term econometric Model of world natural rubber price Standard Malaysia Rubber Grade 20(SMR20). Both Single and simultaneous Equations were utilized using monthly data from January 1990-December 2008 as estimation period and data from January 2009-June 2009 was used as an ex-ante forecast. The data were tested for unit root and Vector Error Correction and co-integration method was used to estimate the parameters of the Model. The Models specifications were developed in order to discover the inter-relationships between NR production, consumption and prices of SMR20 and to determine forecast price of SMR20. Comparative analysis between the Single-Equation specification and simultaneous supply-demand and price Equation were made in terms of their estimation accuracy based on RMSE, MAE and (U-Thile) criteria. Ex-ante forecasts was carried out for the period of January 2009-June 2009. The results revealed that the values of the RMSE, MAE and U of simultaneous supply-demand and price Equations Model were comparatively smaller than the values generated by the Single-Equation Model. These statistics suggest that the simultaneous Equation of supply-demand and price Model is more accurate and efficient measure in terms of its statistical criteria than the Single-Equation Model in predicting the price of SMR20 in the next 6 months.