On trends and constants in periodic autoregressions

Periodic autoregressions are characterised by autoregressive structures that vary with the season. If a time series is periodically integrated, one needs a seasonally varying differencing filter to remove the stochastic trend. When the periodic regression model contains constants and trends with unrestricted parameters, the data can show diverging seasonal deterministic trends. In this paper we derive explicit expressions for parameter restrictions that result in common deterministic trends under periodic trend stationarity and periodic integration.     

The World Social Situation: Development Challenges at the Outset of a New Century

World social development has arrived at a critical turning point. Economically advanced nations have made significant progress toward meeting the basic needs of their populations; however, the majority of developing countries have not. Problems of rapid population growth, failing economies, famine, environmental devastation, majority-minority group conflicts, increasing militarization, among others, are pushing many developing nations toward the brink of social chaos. This paper focuses on worldwide development trends for the 40-year period 1970–2009. Particular attention is given to the disparities in development that exist between the world’s “rich” and “poor” countries as well as the global forces that sustain these disparities. The paper also discusses more recent positive trends occurring within the world’s “socially least developed countries” (SLDCs), especially those located in Africa and Asia, in reducing poverty and in promoting improved quality of life for increasing numbers of their populations.     

THE PROCESS OF CHANGE IN COUPLES THERAPY: A QUALITATIVE INVESTIGATION

Open-ended interviews with 24 couples therapy clients regarding their experience of the process of change revealed shifts in clusters of affect, communication, and cognition. Six additional contextual preconditions for change were also identified. The change process within couples was uniformly reported to be gradual.     

Do worker absences affect productivity? The case of teachers

This article studies the impact of teacher absences on education. Using data spanning three academic years about 285 teachers and 8,631 predominantly economically disadvantaged students from a United States urban school district, it tests assumptions that a substantial portion of teachers' absences is discretionary and that these absences reduce productivity – students' mathematics scores. Since absent teachers are typically replaced by less qualified substitutes, instructional intensity and consistency may decline: ten days of teacher absence reduce students' achievement score by about 3.3 per cent of a standard deviation – enough to lower some students' designation in the state proficiency system and, thus, their motivation to succeed.     

Cramér‐von Mises statistics for discrete distributions with unknown parameters

Choulakian, Lockhart & Stephens (1994) proposed Cramér‐von Mises statistics for testing fit to a fully specified discrete distribution. The authors give slightly modified definitions for these statistics and determine their asymptotic behaviour in the case when unknown parameters in the distribution must be estimated from the sample data. They also present two examples of applications.     

Urban tree cover: an ecological perspective

Analysis of urban tree cover is generally limited to inventories of tree structure and composition on public lands. This approach provided valuable information for resource management. However, it does not account for all tree cover within an urban landscape, thus providing insufficient information on ecological patterns and processes. We propose evaluating tree cover for an entire urban area that is based on patch dynamics. Treed patches are classified by their origin, structure, and management intensity. A patch approach enables ecologists to evaluate ecological patterns and processes for the entire urban landscape and to examine how social patterns influence these ecological patterns and processes.