Introduction

Bekker, Paul; Merckens, Arjen; Wansbeek, Tom

doi:10.1016/b978-0-12-084775-4.50005-6

Cited by 16 publications

(29 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Habitat fragmentation is splitting of natural habitats and ecosystems into smaller, more isolated patches driven by many different factors like disturbance, pollution, settlement, infrastructure, and deforestation [1]. It is the main process responsible for biodiversity loss and threat in tropical forests leading to isolation [2].…”

Section: Introductionmentioning

confidence: 99%

Threats to Mammals on Fragmented Habitats around Asella Town, Central Ethiopia

Kasso

Bekele

2014

International Journal of Biodiversity

View full text Add to dashboard Cite

Assessment of the current information on the major threat to mammals in fragmented remnant montane forest of Child Care Center and School of Agriculture was conducted from March to July 2013. The prevailing threatening factors were collected by questionnaires, checklists, interview, observation, and document analysis. A total of 22 species of mammals were recorded of which six (27%) were endemic to the country and vulnerable. Mammals and their habitats were threatened by land fragmentation, hunting, habitat modification, land degradation and deforestation, lack of awareness, and finance. Although all mammals were susceptible to hunting, high rate of occurrence was recorded for Olive baboon (Papio anubis). The different infrastructure construction in both compounds is causing different impacts. As the area is rich in mammals and other species and threatened by different factors to reverse the situation, urgent conservation action is highly recommended.

show abstract

Section: Introductionmentioning

confidence: 99%

Threats to Mammals on Fragmented Habitats around Asella Town, Central Ethiopia

Kasso

Bekele

2014

International Journal of Biodiversity

View full text Add to dashboard Cite

show abstract

“…Computer algebra systems (CASs) can address the first two issues when symbols replace the estimated values. In fact, Bekker, Merckens, and Wansbeek (1994) propose using a CAS to assess local identification based on the Wald Rank Rule. They use the Jacobian matrix of the covariance matrix and the matrix of restrictions on parameters and examine the rank of the resulting matrix to check for local identification.…”

Section: Local and Global Identificationmentioning

confidence: 99%

“…

J (θ) = [\begin{matrix} \partial σ (θ) / \partial {bold-italicθ}^{'} \\ \partial ρ (θ) / \partial {bold-italicθ}^{'} \end{matrix}]

and show that if θ o is a regular point of J ( θ ), then a necessary and sufficient condition for a locally identified θ o is that J ( θ ) has rank equal to the dimension of θ (Bekker, et al, 1994, pp. 27–28).…”

Section: Local and Global Identificationmentioning

confidence: 99%

“…The Bekker, et al (1994) approach was the first systematic application to CAS checks on local identification in SEM and we see it as a valuable supplement to the usual check on the singularity of the estimated information matrix. Though the Bekker, et al (1994) book and software are out-of-print, CAS software are available to write code to provide this check as we will illustrate.…”

Section: Local and Global Identificationmentioning

confidence: 99%

“…In addition, we use the Wald Rank Rule (Wald, 1950; Bollen, 1989, pages 248-49) to evaluate rank. This CAS approach to local identification is well worked out in Bekker, Merckens, and Wansbeek (1994) who developed software to check local identification based on the Wald Rank Rule (the rank of a Jacobian matrix). This is closely related to the check on the singularity of the information matrix, except the evaluation occurs on the Jacobian matrix which involves first order derivatives rather than second order derivatives.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Model Identification and Computer Algebra

Bollen

Bauldry

2010

Sociological Methods & Research

View full text Add to dashboard Cite

Multiequation models that contain observed or latent variables are common in the social sciences. To determine whether unique parameter values exist for such models, one needs to assess model identification. In practice analysts rely on empirical checks that evaluate the singularity of the information matrix evaluated at sample estimates of parameters. The discrepancy between estimates and population values, the limitations of numerical assessments of ranks, and the difference between local and global identification make this practice less than perfect. In this paper we outline how to use computer algebra systems (CAS) to determine the local and global identification of multiequation models with or without latent variables. We demonstrate a symbolic CAS approach to local identification and develop a CAS approach to obtain explicit algebraic solutions for each of the model parameters. We illustrate the procedures with several examples, including a new proof of the identification of a model for handling missing data using auxiliary variables. We present an identification procedure for Structural Equation Models that makes use of CAS and that is a useful complement to current methods.

show abstract

GE Covariance Through Phenotype to Environment Transmission: An Assessment in Longitudinal Twin Data and Application to Childhood Anxiety

et al. 2014

View full text Add to dashboard Cite

We considered identification of phenotype (at occasion t) to environment (at occasion t + 1) transmission in longitudinal model comprising genetic, common and unique environmental simplex models (autoregressions). This type of transmission, which gives rise to genotype-environment covariance, is considered to be important in developmental psychology. Having established identifying constraints, we addressed the issue of statistical power to detect such transmission given a limited set of parameter values. The power is very poor in the ACE simplex, but is good in the AE model. We investigated misspecification, and found that fitting the standard ACE simplex to covariance matrices generated by an AE simplex with phenotype to E transmission produces the particular result of a rank 1 C (common environment) covariance matrix with positive transmission, and a rank 1 D (dominance) matrix given negative transmission. We applied the models to mother ratings of anxiety in female twins (aged 3, 7, 10, and 12 years), and obtained support for the positive effect of one twin’s phenotype on the other twin’s environment.

show abstract

Introduction

Cited by 16 publications

References 0 publications

Threats to Mammals on Fragmented Habitats around Asella Town, Central Ethiopia

Threats to Mammals on Fragmented Habitats around Asella Town, Central Ethiopia

Model Identification and Computer Algebra

GE Covariance Through Phenotype to Environment Transmission: An Assessment in Longitudinal Twin Data and Application to Childhood Anxiety

Contact Info

Product

Resources

About