Tests for cycling in a signalling pathway

Summary.  Cellular signalling pathways, mediating receptor activity to nuclear gene activation, are generally regarded as feed forward cascades. We analyse measured data of a partially observed signalling pathway and address the question of possible feed-back cycling of involved biochemical components between the nucleus and cytoplasm. First we address the question of cycling in general, starting from basic assumptions about the system. We reformulate the problem as a statistical test leading to likelihood ratio tests under non-standard conditions. We find that the modelling approach without cycling is rejected. Afterwards, to differentiate two different transport mechanisms within the nucleus, we derive the appropriate dynamical models which lead to two systems of ordinary differential equations. To compare both models we apply a statistical testing procedure that is based on bootstrap distributions. We find that one of both transport mechanisms leads to a dynamical model which is rejected whereas the other model is satisfactory.     

SOCIAL SECURITY AND AGGREGATE CAPITAL ACCUMULATION REVISITED: DYNAMIC SIMULTANEOUS ESTIMATES IN A WEALTH-GENERATION MODEL

This paper re-examines Feldstein's(1974, 1982)results of the effect of social security on private capital accumulation in the context of a simultaneous-equation model of capital accumulation. The model incorporates dynamic feedback effects in capital accumulation and is estimated by FIML to incorporate theoretical restrictions that are tested against the data. It is then simulated as a full dynamic model to analyze the long-run effect of SSW on private capital accumulation. The simulated effects are in the same direction as found by Feldstein, but are considerably weaker.     

Pre- and post-planned evaluation: Which is preferable?

This paper compares the advantages and disadvantages of the “pre-planned” and “post-planned” approaches to evaluating program effectiveness. These evaluative approaches are compared along a number of dimensions which include: (a) Reliability of data and the cost of collecting it; (b) Internal validity; (c) External validity; (d) Evaluation obtrusiveness and threat; and (e) Program goal displacement and program direction. A model designed to help program managers decide when and under what conditions either of these two evaluative approaches should be employed is presented. One major theme throughout this discussion is that despite the growing interest in and use of pre-planned evaluation, the post-planned method has many advantages which often go unnoticed. This paper will help program administrators, planners and evaluators in selecting and implementing these two methods in light of their respective strengths and limitations.     

Physicians lead the way at America's top hospitals

The 100 Top hospitals are selected annually based on seven critical parameters for each of the 6,200-plus U.S. hospitals with 25 or more beds. They include the previous year's risk-adjusted patient mortality and complication rates, severity-adjusted average patient lengths of stay, expenses, profitability, proportional outpatient revenue, and asset turnover ratio (a measure of facility and technological pace-keeping ability). The winners are selected from five comparable size groupings--small, medium, large community, teaching, and large academic hospitals. Conspicuous among the winners at every level are physician-led organizations. Even in the majority of hospitals headed by non-physician administrators, however, the managerial capabilities of medical directors are the key to success. The most common characteristic of these award-winning hospitals is that the leadership is working together and communicating the institution's goals effectively to all levels of the organization.     

Two Novel Evolutionary Formulations of the Graph Coloring Problem

We introduce two novel evolutionary formulations of the problem of coloring the nodes of a graph. The first formulation is based on the relationship that exists between a graph's chromatic number and its acyclic orientations. It views such orientations as individuals and evolves them with the aid of evolutionary operators that are very heavily based on the structure of the graph and its acyclic orientations. The second formulation, unlike the first one, does not tackle one graph at a time, but rather aims at evolving a program to color all graphs belonging to a class whose members all have the same number of nodes and other common attributes. The heuristics that result from these formulations have been tested on some of the Second DIMACS Implementation Challenge benchmark graphs, and have been found to be competitive when compared to the several other heuristics that have also been tested on those graphs.