A NOTE ON EVANESCENT PROCESSES

This note examines the connection between μ-invariant measures for the transition function of a continuous-time Markov chain and those of its q-matrix, Q. The major result establishes a necessary and aufficient condition for a convergent μ-invariant measure for Q to be μ-inhant for the minimal transition function, P, under the assumption that P is honest. This corrects Theorem 6 of Vere-Jones (1969) and the first part of Corollary 1 of Pollett (1986), both of which assert that the above conclusion holds in the absence of this condition. The error was pointed out by E.A. van Doom (1991) and the counterexample which be presented provides the basis for the present arguments. In determining where the error occurred in the original proof, we are able to identify a simple sufficient condition for μ-invariance.     

Net migration and migration effectiveness: A comparison between Australia and the United Kingdom, 1976–96

This paper explores the impact of net migration in Australia and the United Kingdom using measures of migration effectiveness computed from period-age migration data for four consecutive five-year periods. Results reported in Part 1 of this paper (Stillwellet al. 2000) suggest that while the overall effectiveness of net migration at the scale of city regions has declined over the twenty-year period in both countries, important geographical variations are evident. Part 2 considers how patterns of migration effectiveness vary by age and presents a single classification of all the city regions on the basis of age-specific effectiveness. More detailed analysis includes spatial patterns for particular age groups and net migration profiles of selected regions. Cohort effects are shown to be important for explaining changes between time periods in these regions.     

Locally optimal designs for the simple death process

We demonstrate the existence and uniqueness of optimal observation schedules for discrete observation of the simple death process. Optimality is framed in the sense of observing the process at times that maximise the Fisher information for the death rate. We examine the relationship of our designs with those obtained by other authors for the simple birth process. A number of interesting properties are uncovered. Practical considerations in the application of these designs in an experimental setting are investigated, and we examine the performance of some approximately optimal designs that are usually simpler to implement. We will show that our optimal designs are highly robust to mis-specification of the death rate.     

The Statistics of Simulating Chaos

When simulating a dynamical system, the computation is actually of a spatially discretized system, because finite machine arithmetic replaces continuum state space. For chaotic dynamical systems, the discretized simulations often have collapsing effects, to a fixed point or to short cycles. Statistical properties of these phenomena can be modelled with random mappings with an absorbing centre. The model gives results which are very much in line with computational experiments. The effects are discussed with special reference to the family of mappings f (x)=1-|1-2x|,x [0,1],1,<,,<,. Computer experiments show close agreement with predictions of the model.     

Effect of perceived cost on judgments regarding the efficacy of investment

Three experiments examined the effect of costs associated with investments on the judgments of the causal effectiveness of those investments, and on the type of information utilised when making those judgements. Using operant conditioning technology, in an experimental analogue of making economic investments, it was found that greater costs associated with an investment reduced the judgement about the effectiveness of the response (Experiment 1). Greater investment costs tended to bias the subject toward using information integrated over a longer period of time; whereas low costs tended to produce judgements made on the basis of the conditions prevailing immediately prior to the return being acquired (Experiments 1–3). The effect of cost was modulated by the subjects' own financial background. The same absolute cost being treated as “greater” by those from less wealthy backgrounds compared to those from more affluent backgrounds (Experiments 2 and 3). These results suggest that as well as the nature of the schedule relating investment to return, the perceived cost of the investment determines the manner in which it is judged with respect to its efficacy.     

Social workers in private practice: What are they really doing?

At one level, private practice may represent a fairly evolved manifestation of the expanded professional growth and sophistication of the individual social worker who embarks upon this highly individualized proprietary enterprise. However, on a larger scale, this widespread shift toward private practice may indicate a collective disenchantment with agency practice per se and represent a concerted attempt to redefine the fundamental aims and values of social work practice.     

Exposure to occupational violence and the buffering effects of intra-oranizational support

This paper presents a conceptually distinct analysis of the data first reported by Leather et al. Specifically, it investigates the effects of exposure to a variety of forms of work-related violence upon work attitudes and general well-being within a sample of UK public house licensees—individuals who manage public houses and hold the licence permitting the sale of alcoholic drinks on the premises. In addition, it examines the role of social support in moderating such effects. Based upon a sample of 242 licensees, it reports a consistent interaction between exposure to such violence and the availability of perceived intra-organizational support in determining the size of any negative effects upon individual well-being, job satisfaction and organizational commitment. It is argued that exposure to all forms of work-related violence, including intimidation, verbal abuse and threat, should be seen as a potential stressor within the work environment, the negative effects of which are buffered by perceived support from within the organization, but not by that perceived to be available from informal sources such as family and friends.