Technical Uncertainty in Quantitative Policy Analysis — A Sulfur Air Pollution Example

Expert judgments expressed as subjective probability distributions provide an appropriate means of incorporating technical uncertainty in some quantitative policy studies. Judgments and distributions obtained from several experts allow one to explore the extent to which the conclusions reached in such a study depend on which expert one talks to. For the case of sulfur air pollution from coal-fired power plants, estimates of sulfur mass balance as a function of plume flight time are shown to vary little across the range of opinions of leading atmospheric scientists while estimates of possible health impacts are shown to vary widely across the range of opinions of leading scientists in air pollution health effects.     

Modelling age variation in survival and reporting rates for recovery models

In this paper, we focus on models for recovery data from birds ringed as young. In some cases, it is important to be able to include in these models a degree of age variation in the reporting probability. For certain models this has been found, empirically, to result in completely flat likelihood surfaces, due to parameter redundancy. These models cannot then be fitted to the data, to produce unique parameter estimates. However, empirical evidence also exists that other models with such age variation can be fitted to data by maximum likelihood. Using the approach of Catchpole and Morgan (1996b), we can now identify which models in this area are parameter-redundant, and which are not. Models which are not parameter-redundant may still perform poorly in practice, and this is investigated through examples, involving both real and simulated data. The Akaike Information Criterion is found to select inappropriate models in a number of instances. The paper ends with guidelines for fitting models to data from birds ringed as young, when age dependence is expected in the reporting probability.     

Putting modularity in business planning and control

The use of modules in constructing corporate planning systems has been reported by companies such as I.B.M. Xerox, and Standard Oil of New Jersey. The modules may be of organizational units, or of functions such as production, distribution and finance. Modules may also be used for different types of calculations and for generating report output. A module is quite simply a standard unit. Modularity becomes more important as systems grow large, because it is one means of keeping order within large systems. Modularisation is a key concept in structuring large systems, and a useful approach to use in designing procedures for Corporate Planning.     

Intention and uncertainty at later stages of childbearing: the united states 1965 and 1970

While births may be dichotomous, fertility intentions are not inherently so. Intentions are predictions about the future and, as such, are couched in considerable uncertainty. Ignoring this uncertainty hides much of what could be learned from data on fertility intentions. This paper presents a model which allows analysis of the full range of intentions. After selecting a sample of women in the later stage of childbearing (e.g., those who intend fewer than two additional children) from the 1965and 1970 National Fertility Studies, it is shown that: (1) substantial portions of women at this stage of the reproductive life cycle were indeed uncertain of their parity-specific intention; (2) this certainty, like more firm intentions, varies by age and parity as the model predicts; and (3) there were significant shifts in the level of certainty between 1965 and 1970. Specifically, while intentions for third, fourth, and fifth births declined, more women “didn’t know” if they intended to have another child or not. Among those not intending another child, more seemed uncertain of this intention in 1970 than did comparable women in 1965. In contrast, those intending another child seemed more certain. These changes in intention and uncertainty indicate that the observed decline in intended parity was tentative. Post-1970 evidence suggests that this tentative decline has become an unequivocal one.     

Automatic starting point selection for function optimization

Traditional (non-stochastic) iterative methods for optimizing functions with multiple optima require a good procedure for selecting starting points. This paper illustrates how the selection of starting points can be made automatically by using a method based upon simulated annealing. We present a hybrid algorithm, possessing the accuracy of traditional routines, whilst incorporating the reliability of annealing methods, and illustrate its performance for a particularly complex practical problem.Now at the Statistical Laboratory, University of Cambridge, 16 Mill Lane, Cambridge, CB2 1SB, UK.