Detecting structural change with heteroskedasticity

The hypothesis of structural stability that the regression coefficients do not change over time is central to all applications of linear regression models. It is rather surprising that existing theory as well as practice focus on testing for structural change under homoskedasticity – that is, regression coefficients may change, but the variances remain the same. Since structural change can, and often does, involve changes in variances, this is a puzzling gap in the literature. Our main focus in this paper is to utilize a newly developed test (MZ) by Maasoumi et al. (2010 Maasoumi, E., Zaman, A., Ahmed, M. (2010). Tests for structural change, aggregation, and homogeneity. Econ Model. 27(6):1382–1391.[Crossref], [Web of Science ®] , [Google Scholar]) that tests simultaneously for break in regression coefficients as well as in variance. Currently, the sup F test is most widely used for structural change. This has certain optimality properties shown by Andrews (1993 Andrews, D.W.K. (1993). Test for parameter instability and structural change with unknown change point. Econometrica. 61(4):821–856.[Crossref], [Web of Science ®] , [Google Scholar]). However, this test assumes homoskedasticity across the structural change. We introduce the sup MZ test which caters to unknown breakpoints, and also compare it to the sup F. Our Monte Carlo results show that sup MZ test incurs only a low cost in case of homoskedasticity while having hugely better performance in case of heteroskedasticity. The simulation results are further supported by providing a real-world application. In real-world datasets, we find that structural change often involves heteroskedasticity. In such cases, the sup F test can fail to detect structural breaks and give misleading results, while the sup MZ test works well. We conclude that the sup MZ test is superior to current methodology for detecting structural change.     

A conceptual model for the process of IT innovation adoption in organizations

In this paper, we develop a conceptual model for IT innovation adoption process in organizations. The model utilizes Diffusion of Innovation (DOI) theory, Theory of Reasoned Action (TRA), Technology Acceptance Model (TAM), Theory of Planned Behaviour (TPB) and a framework that contains characteristics of innovation, organization, environment, chief executive officer (CEO) and user acceptance. The model presents IT adoption as a sequence of stages, progressing from initiation to adoption-decision to implementation. The study presents a model with an interactive process perspective which considers organizational level analysis until acquisition of technology and individual level analysis for the user acceptance of IT.     

The Changing Transmission of Uncertainty Shocks in the U.S.

This article investigates if the impact of uncertainty shocks on the U.S. economy has changed over time. To this end, we develop an extended factor augmented vector autoregression (VAR) model that simultaneously allows the estimation of a measure of uncertainty and its time-varying impact on a range of variables. We find that the impact of uncertainty shocks on real activity and financial variables has declined systematically over time. In contrast, the response of inflation and the short-term interest rate to this shock has remained fairly stable. Simulations from a nonlinear dynamic stochastic general equilibrium (DSGE) model suggest that these empirical results are consistent with an increase in the monetary authorities’ antiinflation stance and a “flattening” of the Phillips curve. Supplementary materials for this article are available online.     

Child Sexual Abuse in Zimbabwe

Although child sexual abuse is a significant public health problem globally, its incidence, prevention, and management is less well described in resource-poor settings. In poorer settings prevention initiatives assume even more importance since resources for managing abused children are severely limited. This article examines the current status of policy and practice related to the prevention of child sexual abuse in Zimbabwe. It identifies implementation challenges and highlights opportunities that could be embraced to reduce CSA in Zimbabwe, based on evidence synthesized from recent work. Although Zimbabwe has a well-established legal and regulatory framework to protect children from child sexual abuse, implementation of existing policies is weak. Financial, human, and material resource constraints are frequently cited to explain limited prevention activity. Effective strategies for the prevention of child sexual abuse should focus on implementing existing legislation, targeting schoolchildren, and getting community involvement. A dedicated budget would help entrench these strategies, but gains can be achieved even in the absence of this.     

Globalization and the Quality of Government: an Analysis of the Relationship

This research seeks to investigate the relationship between globalization and the quality of government. By using the Quality of Government Institute data, the paper analyzes the relationships between globalization and the government quality. The paper uses both KOF scores and the scores by the Heritage Foundation to measure globalization. The results show that economic and political globalization is a significant predictor of the quality of government. When all the variables on economic freedom are taken into consideration, fiscal, business and trade freedoms are critical factors influencing the quality of governance.     

Testing for Additivity at Select Mixture Groups of Interest Based on Statistical Equivalence Testing Methods

Several assumptions, defined and undefined, are used in the toxicity assessment of chemical mixtures. In scientific practice mixture components in the low-dose region, particularly subthreshold doses, are often assumed to behave additively (i.e., zero interaction) based on heuristic arguments. This assumption has important implications in the practice of risk assessment, but has not been experimentally tested. We have developed methodology to test for additivity in the sense of Berenbaum (Advances in Cancer Research, 1981), based on the statistical equivalence testing literature where the null hypothesis of interaction is rejected for the alternative hypothesis of additivity when data support the claim. The implication of this approach is that conclusions of additivity are made with a false positive rate controlled by the experimenter. The claim of additivity is based on prespecified additivity margins, which are chosen using expert biological judgment such that small deviations from additivity, which are not considered to be biologically important, are not statistically significant. This approach is in contrast to the usual hypothesis-testing framework that assumes additivity in the null hypothesis and rejects when there is significant evidence of interaction. In this scenario, failure to reject may be due to lack of statistical power making the claim of additivity problematic. The proposed method is illustrated in a mixture of five organophosphorus pesticides that were experimentally evaluated alone and at relevant mixing ratios. Motor activity was assessed in adult male rats following acute exposure. Four low-dose mixture groups were evaluated. Evidence of additivity is found in three of the four low-dose mixture groups. The proposed method tests for additivity of the whole mixture and does not take into account subset interactions (e.g., synergistic, antagonistic) that may have occurred and cancelled each other out.     

Gene‐environment correlations in the cross‐generational transmission of parenting: Grandparenting moderates the effect of child 5‐HTTLPR genotype on mothers' parenting

Evidence suggests that parenting is associated cross‐generationally and that children's genes may elicit specific parenting styles (evocative gene‐environment correlation). This study examined whether the effect of children's genotype, specifically 5‐HTTLPR, on mothers' parenting behaviors was moderated by her own parenting experiences from her mother. Two independent samples of three‐year‐olds (N = 476 and 405) were genotyped for the serotonin transporter gene, and observational measures of parenting were collected. Mothers completed measures of the parenting they received as children. The child having a short allele on 5‐HTTLPR was associated with more maternal hostility (Samples 1 and 2) and with less maternal support (Sample 1), but only if the mother reported lower quality grandmothers' parenting (abuse and indifference in Sample 1 and lower levels of grandmother care in Sample 2). Results support the possibility of a moderated evocative gene‐environment correlation.     

Stochastic analysis of a complex system with an auxiliary unit

This paper considers the stochastic analysis of a complex system having three units. The first two units are designated as unit-1 and unit-2 while the third unit is called an auxiliary unit (unit-3) which enhances the range of transmission and efficiency of unit-1. Joint distributions of failure and repair times are bivariate exponential (B.V.E.) with different parameters. Regenerative point technique is used to obtain various reliability characteristics of the system under study. Behaviour of some characteristics has also been studied through graphs.