City University London

About: City University London is a education organization based out in London, United Kingdom. It is known for research contribution in the topics: Population & Context (language use). The organization has 5735 authors who have published 17285 publications receiving 453290 citations.

Mortality Density Forecasts: An Analysis of Six Stochastic Mortality Models

Abstract: We investigate the uncertainty of forecasts of future mortality generated by a number of previously proposed stochastic mortality models. We specify fully the stochastic structure of the models to enable them to generate forecasts. Mortality fan charts are then used to compare and contrast the models, with the conclusion that model risk can be significant. The models are also assessed individually with reference to three criteria that focus on the plausibility of their forecasts: biological reasonableness of forecast mortality term structures; biological reasonableness of individual stochastic components of the forecasting model (for example, the cohort erect); and reasonableness of forecast levels of uncertainty relative to historical levels of uncertainty. In addition, we consider a fourth assessment criterion dealing with the robustness of forecasts relative to the sample period used to fit the model. To illustrate the assessment methodology, we analyse a data set consisting of national population data for England & Wales, for Males aged between 60 and 90 years old. We note that this particular data set may favour those models designed for application to older ages, such as variants of Cairns-Blake-Dowd, and emphasise that a similar analysis should be conducted for the specific data set of interest to the reader. We draw some conclusions based on the analysis and compare to the application of the models for the same age group and gender for the United States population. Finally, we note the broader application of the approach to model selection for alternate data sets and populations

Conceptual modeling of coincident failures in multiversion software

Abstract: Work by D.E. Eckhardt and L.D. Lee (1985), shows that independently developed program versions fail dependently. The authors show that there is a precise duality between input choice and program choice in this model and consider a generalization in which different versions can be developed using diverse methodologies. The use of diverse methodologies is shown to decrease the probability of the simultaneous failure of several versions. Indeed, it is theoretically possible to obtain versions which exhibit better than independent failure behavior. The authors formalize the notion of methodological diversity by considering the sequence of decision outcomes that constitute a methodology. They show that diversity of decision implies likely diversity of behavior for the different versions developed under such forced diversity. For certain one-out-of-n systems the authors obtain an optimal method for allocating diversity between versions. For two-out-of-three systems there seem to be no simple optimality results which do not depend on constraints which cannot be verified in practice. >

Words, nonwords, and phonological processes: Some comments on Gathercole, Willis, Emslie, and Baddeley

Abstract: Gathercole, Willis, Emslie, and Baddeley (1991) present a reanalysis of some of their earlier data concerned with the relationship between nonword repetition and the development of vocabulary knowledge in young children. In the present article we outline some theoretical differences between ourselves and this group in the interpretation of nonword repetition and discuss how best these differences could be resolved.

Does Twitter matter? The impact of microblogging word of mouth on consumers’ adoption of new movies

Abstract: This research provides an empirical test of the “Twitter effect,” which postulates that microblogging word of mouth (MWOM) shared through Twitter and similar services affects early product adoption behaviors by immediately disseminating consumers’ post-purchase quality evaluations. This is a potentially crucial factor for the success of experiential media products and other products whose distribution strategy relies on a hyped release. Studying the four million MWOM messages sent via Twitter concerning 105 movies on their respective opening weekends, the authors find support for the Twitter effect and report evidence of a negativity bias. In a follow-up incident study of 600 Twitter users who decided not to see a movie based on negative MWOM, the authors shed additional light on the Twitter effect by investigating how consumers use MWOM information in their decision-making processes and describing MWOM’s defining characteristics. They use these insights to position MWOM in the word-of-mouth landscape, to identify future word-of-mouth research opportunities based on this conceptual positioning, and to develop managerial implications.