Projectors and linear estimation in general linear models

The paper gives a self-contained account of minimum disper­sion linear unbiased estimation of the expectation vector in a linear model with the dispersion matrix belonging to some, rather arbitrary, set of nonnegative definite matrices. The approach to linear estimation in general linear models recommended here is a direct generalization of some ideas and results presented by Rao (1973, 19 74) for the case of a general Gauss-Markov model

A new insight into the nature of some estimation problems originaly arising in the context of a general Gauss-Markov model as well as the correspondence of results known in the literature to those obtained in the present paper for general linear models are also given. As preliminary results the theory of projectors defined by Rao (1973) is extended.     

Estimation in singular partitioned,reduced or transformed linear models

A singular partitioned linear model, i.e. the singular model comprising the main parameters and the nuisance parameters, can be reduced, or transformed to the form in which only linear functions concerning main parameters are involved. In the paper some properties of the best linear unbiased estimators of these functions following from these models are considered.     

Two-phase nonlinear regression with smooth transition

A method of estimating parameters of twophase nonlinear regression with smooth transition between phases is described. It consists of two stages, both utilizing the least square fit. In the first one, each phase is fitted separately and, simultaneously, a transition point is determined. In the second stage, the two phases are joined smoothly by a proper transition function, which depends on the transition point chosen by the grid search. The practical aspects of the method proposed are demonstrated on the data concerning the soil bulk density in dependence on the soil water content.     

Some methods for constructing efficiency-balanced block designs

Three methods are presented for constructing connected efficiency-balanced block designs from other block designs with the same properties. The resulting designs differ from the original ones in the number of blocks and/or in the number of experimental units and their arrangement, while the number of treatments remains unaltered. Some remarks on the proposed methods of construction refer also to variance-balanced block designs.     

On equalities between BLUES,WLSEs, and SLSEs

Necessary and sufficient conditions for equalities between the best linear unbiased estimator, the weighted least-squares estimator, and the simple least-squares estimator of the expectation vector in a general Gauss-Markoff model are given in some alternative formulations. The main result states, somewhat surprisingly, that the weighted least-squares estimator cannot be identical with the simple least-squares estimator unless they both coincide with the best linear unbiased estimator.     

Approximate confidence intervals for a ratio of two variance components

New approximate confidence intervals for the ratio of two variance components in an unbalanced mixed .linear model with a single set of random effects are proposed. Contrary to the confidence intervals known in the literature the new intervals preserve the confidence coefficient and cover the exact confidence interval which, however, is not easy to establish as it requires the solution of complicated nonlinear equations.     

On nested block designs geometry

Nested block designs and block designs properties such as orthogonality, orthogonal block structure and general balance are examined using the concept of a commutative quadratic subspace and standard properties of orthogonal projectors. In this geometrical context conditions for existence of the best linear unbiased estimators of treatment contrasts are also discussed.     

Geographic variation in surgical treatment for work-related carpal tunnel syndrome: does improved return to work matter?

Medical treatment of compensated work-related conditions has two objectives--improve injured workers' health status and allow safe and sustained return to work (RTW). Theoretically, the choice of treatment method should be based primarily on these objectives. Surgical treatment of work-related carpal tunnel syndrome (CTS) provides an opportunity to evaluate whether this occurs. The traditional method of open release has been complemented by an endoscopic procedure, particularly useful in work-related cases due to the anticipated benefit of earlier RTW. The objective of this study was to investigate the differences in surgical treatment for work-related CTS across eight US workers' compensation (WC) jurisdictions, and the factors associated with these differences. From all WC claims reported to a single insurer during the 1995-1999 period, we identified individuals with a one or two surgical procedures for work-related CTS. Among selected individuals (n=4,421), about 20% were treated using the endoscopic procedure; this percentage had a ten-fold variation across the eight jurisdictions. However, utilization of endoscopic release did not increase during the study period, despite reports of better RTW outcomes. The highly jurisdictional nature of the US WC system, with significant differences in reimbursement levels for endoscopic procedures, and geographical differences in medical training were among the potential contributors to the observed variation in utilization.     

Forging and sustaining research-minded professionals: teaching undergraduate research through student-community partnerships

The teaching of research is a well-established core component of social work curricula around the world. While educators in social work recognize the value, and need for research they have encountered persistent discomfort and reluctance from students to recognize this need. Practitioners in the field of social work often share this reserve either due to limited self-efficacy with regard to research knowledge and skills or practical constraints. With the growing need for practice-based knowledge, accountability and evidence-based practices to drive outcomes and service effectiveness, it is becoming imperative to not only prepare future social work professionals with the required skill sets but also support current professionals to meet these expectations. This paper showcases a pedagogical endeavor with an undergraduate research course in an American rural university, designed and implemented to create and support research-minded professionals through student–agency research partnerships. Through a collaborative, service-oriented learning, students have gained a new appreciation for research and agency connections while agencies have welcomed the path created to pursue their research agenda. This experience has valuable implications for research capacity building, and for community engaged research empowering future and current professionals to suitably use research toward effective and meaningful service provision.     

Change resistance moderates existence and longevity biases

Evidence has been found for existence and longevity biases—inferences of goodness from prevalence or longevity. We argue these biases actually emerge among change-resisting individuals. Our evidence suggests change-accepting individuals can even demonstrate a reversal of these biases. In two studies, change-resisting individuals’ attitudes were suggestive of existence and longevity biases while change-accepting individuals significantly reversed this pattern by evaluating long-standing or prevalent objects less favorably. Finally, we reanalyzed data from the existence and longevity biases literature previously reported in Social Influence. We found Americans identifying as more Republican—thus theorized as more change-resisting—were those who favored a long-standing practice. Altogether, we argue that existence and longevity biases emerge depending on individuals’ change resistance, indicating an important theoretical expansion.