Statistical Methods for the Qualitative Assessment of Dynamic Models with Time Delay (R Package qualV)

Results of ecological models differ, to some extent, more from measured data than from empirical knowledge. Existing techniques for validation based on quantitative assessments sometimes cause an underestimation of the performance of models due to time shifts, accelerations and delays or systematic differences between measurement and simulation. However, for the application of such models it is often more important to reproduce essential patterns instead of seemingly exact numerical values. This paper presents techniques to identify patterns and numerical methods to measure the consistency of patterns between observations and model results. An orthogonal set of deviance measures for absolute, relative and ordinal scale was compiled to provide informations about the type of difference. Furthermore, two different approaches accounting for time shifts were presented. The first one transforms the time to take time delays and speed differences into account. The second one describes known qualitative criteria dividing time series into interval units in accordance to their main features. The methods differ in their basic concepts and in the form of the resulting criteria. Both approaches and the deviance measures discussed are implemented in an R package. All methods are demonstrated by means of water quality measurements and simulation data. The proposed quality criteria allow to recognize systematic differences and time shifts between time series and to conclude about the quantitative and qualitative similarity of patterns.

Financial Fragility and Growth Dynamics of Italian Business Firms

This work explores a number of properties investigated in the empirical literature on firm size and growth dynamics: (i) the distribution and the autoregressive structure of firm size; (ii) the existence of size-growth scaling relationships; (iii) the distribution and the autoregressive structure of scaling-free growth rates. The major novelty concerns our exploiting of a credit rating index to condition all the analyses upon firms' financial fragility and access to credit. We find that the distributions of both firm size and firm growth rates are fatter tailed among less solvable firms than in the rest of the sample, both at the bottom and at the top extreme of the distributions. As a result, we conclude that not only small and/or slowly growing firms might suffer from difficulties in raising external financing, but also big and fast growing ones might be exposed to financial constraints.Firm size, Firm growth, Financial constraints

GlimmerGlass Volume 53 Number 02 (1993)

Official Student Newspaper Issue is 8 pages long

Xavier University Newswire

https://www.exhibit.xavier.edu/student_newspaper/1373/thumbnail.jp

Statistical Methods for the Qualitative Assessment of Dynamic Models with Time Delay (R Package qualV)

Results of ecological models differ, to some extent, more from measured data than from empirical knowledge. Existing techniques for validation based on quantitative assessments sometimes cause an underestimation of the performance of models due to time shifts, accelerations and delays or systematic differences between measurement and simulation. However, for the application of such models it is often more important to reproduce essential patterns instead of seemingly exact numerical values. This paper presents techniques to identify patterns and numerical methods to measure the consistency of patterns between observations and model results. An orthogonal set of deviance measures for absolute, relative and ordinal scale was compiled to provide informations about the type of difference. Furthermore, two different approaches accounting for time shifts were presented. The first one transforms the time to take time delays and speed differences into account. The second one describes known qualitative criteria dividing time series into interval units in accordance to their main features. The methods differ in their basic concepts and in the form of the resulting criteria. Both approaches and the deviance measures discussed are implemented in an R package. All methods are demonstrated by means of water quality measurements and simulation data. The proposed quality criteria allow to recognize systematic differences and time shifts between time series and to conclude about the quantitative and qualitative similarity of patterns

Campus Report, Vol. 33, No. 2

Perspectives on Hurricane Katrina: Four faculty members offer insights — from geography, history, engineering and poverty — on what we\u27ve learned.https://ecommons.udayton.edu/cmps_rpt/1001/thumbnail.jp

Central Florida Future, August 30, 2000

UCF growing in more ways than one; UCF chapter of Golden Key wins again; Three film makers make UCF their home.https://stars.library.ucf.edu/centralfloridafuture/2544/thumbnail.jp