On the Complexity of Constructing Evolutionary Trees

In this paper we study a few important tree optimization problems with applications to computational biology. These problems ask for trees that are consistent with an as large part of the given data as possible. We show that the maximum homeomorphic agreement subtree problem cannot be approximated within a factor of , where N is the input size, for any 0 in polynomial time unless P = NP, even if all the given trees are of height 2. On the other hand, we present an O(N log N)-time heuristic for the restriction of this problem to instances with O(1) trees of height O(1) yielding solutions within a constant factor of the optimum. We prove that the maximum inferred consensus tree problem is NP-complete, and provide a simple, fast heuristic for it yielding solutions within one third of the optimum. We also present a more specialized polynomial-time heuristic for the maximum inferred local consensus tree problem.     

Testing symmetry under a skew Laplace model

We develop tests of hypothesis about symmetry based on samples from possibly asymmetric Laplace distributions and present exact and limiting distribution of the test statistics. We postulate that the test statistic derived under the Laplace model is a rational choice as a measure of skewness and can be used in testing symmetry for other, quite general classes of skew distributions. Our results are applied to foreign exchange rates for 15 currencies.     

Masking methods that preserve positivity constraints in microdata

Statistical agencies have conflicting obligations to protect confidential information provided by respondents to surveys or censuses and to make data available for research and planning activities. When the microdata themselves are to be released, in order to achieve these conflicting objectives, statistical agencies apply statistical disclosure limitation (SDL) methods to the data, such as noise addition, swapping or microaggregation. Some of these methods do not preserve important structure and constraints in the data, such as positivity of some attributes or inequality constraints between attributes. Failure to preserve constraints is not only problematic in terms of data utility, but also may increase disclosure risk.In this paper, we describe a method for SDL that preserves both positivity of attributes and the mean vector and covariance matrix of the original data. The basis of the method is to apply multiplicative noise with the proper, data-dependent covariance structure.     

Governance Structures,Coordination Mechanisms and Cognitive Models

This paper criticizes the current prevailing ways ofmodelling governance alternatives, and advocates theopportunity and feasibility of a reconceptualizationof governance forms as mixes or configurations ofsimpler and potentially disentangleablecomponents. These components are constituted by abundle of property rights and by a set of coordinationmechanisms. The paper draws on a previous effort atintegrating economic, organizational and sociologicaltheories of governance in a cognitive perspective(Grandori 1995a) and explicitates how some cognitivefoundations of organization theory can be revised tosustain a more fine-grained view of governance. Theimplications for organization design are illustratedin the final section through the solution of someempirical design problems, as well as through areinterpretation of known hybrid arrangements.     

Engaging stakeholders through social networking: How nonprofit organizations are using Facebook

Since social networking sites, such as MySpace and Facebook, began allowing organizations to create profiles and become active members, organizations have started incorporating these strategies into their public relations programming. For-profit organizations have used these sites to help launch products and strengthen their existing brands; however, little is known about how nonprofit organizations are taking advantage of the social networking popularity. Through a content analysis of 275 nonprofit organization profiles on Facebook, this study examines how these new social networking sites are being used by the organizations to advance their organization's mission and programs. Solely having a profile will not in itself increase awareness or trigger an influx of participation. Instead careful planning and research will greatly benefit nonprofits as they attempt to develop social networking relationships with their stakeholders.     

Variation in part‐time job quality within the nonprofit human service sector

This article extends the growing literature on the quality of part‐time employment to the domain of nonprofit human services, specifically grassroots organizations in which paid work is itself a relatively new reality. It addresses three central questions: How do part‐time and full‐time workers differ in their personal and household characteristics? How do part‐time jobs differ in access to employment benefits from their full‐time counterparts; and finally, How does benefits access vary among part‐time job titles? These lines of inquiry are examined using data from the populations of nonprofit domestic violence programs and their employees in a large midwestern metropolitan area. Analyses of worker‐level data reveal that part‐time workers in these settings disproportionately live with children, are in committed relationships, and report a strong preference for employment that facilitates work‐life balance; they are also less likely to be primary household wage earners. Analyses at the level of jobs suggest that employment benefits extended to part‐time jobs are minimal compared to their full‐time equivalents, but there are also striking variations among different part‐time titles. The results offer insights into the nature of part‐time work in these nonprofit human service settings and potential challenges for effective management.     

Environmental Tobacco Smoke: Exposure-Response Relationships in Epidemiologic Studies

Demonstration of a dose-response relationship for environmental tobacco smoke (ETS) is an important indication of causality. Central to the analysis and interpretation of dose-response relations as described in epidemiological studies is the relationship between dose and exposure. It must be recognized that in studies of ETS we have only surrogate measures of dose, and these surrogate measures (based on exposure) are imperfect. The question-based measures of ETS exposure generally have not been standardized, may have limited validity and reliability, and cannot comprehensively describe total ETS exposure, exposure to individual ETS components, nor doses of biologically relevant agents at target sites. Nevertheless, useful data have been yielded in epidemiologic studies linking ETS exposure to increased respiratory infection and symptoms, reduced lung growth in children, and increased lung cancer in nonsmoking adults. The more consistent exposure-response data for studies on acute health in children may reflect the greater difficulty in measuring exposure in studies of chronic health in adults.     

A blueprint for career change when you don't know what you want to do

Follow the paths of a gynecologist turned investment banker and an internist who became a medical writer. Both used a proven process to change their careers and determine what they wanted to do.     

Facilitators and barriers to employment: the perspectives of people with psychiatric disabilities and employment service providers

This study examined the perspectives of people with psychiatric disabilities and employment service providers regarding factors that most directly help or hinder consumer efforts to obtain and maintain employment. Forty-four adults with serious mental illness (SMI) (consumers) and 30 providers participated in 12 focus groups across Massachusetts. We began both consumer and provider groups by posing two broad questions: 1) what factors most help people with SMI get and keep jobs (facilitators), and 2) what factors most prevent people with SMI from getting and keeping jobs (barriers)? Data were analyzed qualitatively and both person and environmental factors were highlighted. Among facilitators, participants agreed that quality consumer-provider relationships and individualized employment services are most instrumental in helping consumers achieve employment goals. Participants identified a range of environmental barriers, including issues related to the service system, entitlement programs, non-human resources, and social stigma. Implications for services are discussed.     

Love and Hooking Up in the New Millennium: Communication Technology and Relationships among Urban African American and Puerto Rican Young Adults

Communication technology is a central feature of young people's lives, but its role in romantic and sexual relationships has not been thoroughly examined. This article describes how young adults use communication technology for partnering across relationship stages (formation, maintenance, and dissolution) and types (serious/casual), and proposes implications of usage in relationships. This study analyzed qualitative data from a five-week, prospective, coital diary method with related debriefing interviews (N = 70) of African American and Puerto Rican men and women aged 18 to 25 years in Hartford and Philadelphia. Cell phones, including calls, text messaging, and mobile Internet, were the most common forms of communication technology used for partnering goals. Participants reported using cell phones to pursue partnering goals across all relationship stages, including formation (meeting, screening, and getting to know new partners), maintaining existing relationships, and breaking up. Cell phone uses depended on the type of relationship (serious/casual) and the participants' intentions and desires. Results indicated that cell phones are an important element of communication among young adults in romantic and sexual relationships. Specific features of cell phone communication shape the process and context of partnering. Future research should explore emerging communication technologies and implications for psychosocial development, dating violence, and sexual behavior.