Some Modifications for Choosing Ridge Parameters

Standard least square regression can produce estimates having a large mean squares error (MSE) when predictor variables are highly correlated or multicollinear. In this article, we propose four modifications to choose the ridge parameter (K) when multicollinearity exists among the columns of the design matrix. The proposed new estimators are extended versions of that suggested by Khalaf and Shukur (2005 Khalaf , G. , Shukur , G. ( 2005 ). Choosing ridge parameter for regression problems . Commun. Statist. A 34 : 1177 – 1182 . [CSA] [Taylor & Francis Online] , [Google Scholar]). The properties of these estimators are compared with those of Hoerl and Kennard (1970a Hoerl , A. E. , Kennard , R. W. ( 1970a ). Ridge regression: biased estimation for non-orthogonal problems . Tech. . 12 : 55 – 67 . [CSA] [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) and the OLS using the MSE criterion. All estimators under consideration are evaluated using simulation techniques under certain conditions where a number of factors that may affect their properties have been varied. In addition, it is shown that at least one of the proposed estimators either has a smaller MSE than the others or is the next best otherwise.     

Finite-sample Resampling-based Combined Hypothesis Tests,with Applications to Serial Correlation and Predictability

This article suggests Monte Carlo multiple test procedures which are provably valid in finite samples. These include combination methods originally proposed for independent statistics and further improvements which formalize statistical practice. We also adopt the Monte Carlo test method to noncontinuous combined statistics. The methods suggested are applied to test serial dependence and predictability. In particular, we introduce and analyze new procedures that account for endogenous lag selection. A simulation study illustrates the properties of the proposed methods. Results show that concrete and nonspurious power gains (over standard combination methods) can be achieved through the combined Monte Carlo test approach, and confirm arguments in favor of variance-ratio type criteria.     

Two-person sequential bargaining behavior with exogenous breakdown

We examine bargaining behavior in a noncooperative game in which players alternate in making and responding to proposals over the division of a given surplus. Although the number of bargaining periods is unlimited and time is not discounted, the bargaining is subject to exogenous breakdown at each period with a fixed probability which is common knowledge. We manipulate three probabilities of break-down in a between-subjects design that allows comparison with previous studies of two-person bargaining with time discounting. Assuming that subjects maximize expected utility, and this utility is measured by monetary payoffs, our results reject both the subgame perfect equilibrium and equal split solutions. Data analyses reveal that a substantial percentage of subjects behave adaptively in that they systematically search for the highest acceptable demands.     

Approximate Bayes estimation of the parameters and reliability function of a mixture of two inverse Weibull distributions under Type-2 censoring

The main goal of this paper is to develop the approximate Bayes estimation of the five-dimensional vector of the parameters and reliability function of a mixture of two inverse Weibull distributions (MTIWD) under Type-2 censoring. Usually, the posterior distribution is complicated under the scheme of Type-2 censoring and the integrals that are involved cannot be obtained in a simple explicit form. In this study, we use Lindley's [Approximate Bayesian method, Trabajos Estadist. 31 (1980), pp. 223–237] approximate form of Bayes estimation in the case of an MTIWD under Type-2 censoring. Later, we calculate the estimated risks (ERs) of the Bayes estimates and compare them with the corresponding ERs of the maximum-likelihood estimates through Monte Carlo simulation. Finally, we analyse a real data set using the findings.     

Moments of Order Statistics from Weibull Distribution in the Presence of Multiple Outliers

In this article, we derive exact expressions for the single and product moments of order statistics from Weibull distribution under the contamination model. We assume that X₁, X₂, …, X_{n ? p} are independent with density function f(x) while the remaining, p observations (outliers) X_{n ? p + 1}, …, X_n are independent with density function arises from some modified version of f(x), which is called g(x), in which the location and/or scale parameters have been shifted in value. Next, we investigate the effect of the outliers on the BLUE of the scale parameter. Finally, we deduce some special cases.     

Care Leavers in Israel: What Contributes to Better Adjustment to Life After Care?

ABSTRACT

The present study examines the adjustment of youth leaving residential treatment in Israel in three core areas: military service, accommodation, and financial status. A sample of 277 adolescents (aged 17–18 years old) in educational and welfare residential placements were interviewed a few months before leaving care, and 236 of them were interviewed 1 year after. It was hypothesized that optimism, higher perceived sense of readiness to leave care, and higher social support of family, friends, and staff are associated with better outcomes in adjustment to military service, accommodations, and economic status. Findings show that 70% of care leavers were drafted to the (compulsory) military service, a sign of good adjustment in Israel. Yet, they have significant difficulties in the areas of accommodations and financial status. Optimism and perceived readiness for independent living while still in care were positively correlated with adjustment to the military service. Mother's support was positively correlated with care leavers’ economic status and stability in accommodations. These findings highlight the importance of designing programs that include specific attention to needs and challenges while youth are in care and immediately after they leave. Follow-up and longitudinal studies are suggested.     

Family support as a working style in child protection in Italy: A comparative study on social workers' child welfare attitudes

Comparative studies on child protection decision-making highlight the implications and determinants of differences in child welfare systems internationally and reinforce discussions regarding child protection practices and family support when a child is exposed to inadequate parental care. To date, Italian child protection studies have highlighted a system characterised by a strong degree of variability related to the absence of practices shared nationally. Differently, this comparative study focuses more on similarities within the Italian context, seeking to understand how they influence practices. The opinions of 188 Italian social workers with respect to the substantiation of maltreatment, risk assessment and intervention recommendations were compared with the results of a recent study involving practitioners in Israel, Northern Ireland, Spain and the Netherlands. The main outcomes show that Italian social workers prefer a family support orientation, meaning that children are usually removed from their home only if necessary and generally with the aim of reunification with their families. The study also reveals that Italian professionals are more in favour of residential care than foster care.     

Readiness for independent living of adolescents in youth villages in Israel

Most Israeli children who spend their youth away from their birth parents live in youth villages. The majority of these children come from either the geographical or social periphery of Israel. Since the 1990s the youth villages have specialized in absorbing immigrants mainly from the former Soviet Union (FSU) and Ethiopia. The paper reports on a survey conducted among the professional staff in the youth villages. This study explores their perceptions of the readiness for independent living of adolescents on the verge of leaving youth villages and examines how readiness is associated with individual and familial characteristics. A structured questionnaire was mailed to youth villages asking professionals to anonymously complete the survey. The total sample include reports on 1256 adolescents who spent in the current setting on average 3.3 (SD = 1.8) years. For many of them this was the first out-of-home placement. Generally, workers have a favorable assessment of the youths' readiness for independent living. Still, they report that many of the youths do not have any of the necessary skills for independent living. Additionally, there are sub-groups that are more disadvantaged and at greater risk because they lack skills for a successful transition from care. The findings indicate that youth of Ethiopian origin are more disadvantaged with regard to skills related to school, the job market, finances, interpersonal relationships and normative behaviors, whereas youths from FSU present fewer skills pertaining to military service. The findings emphasize the important role Israeli youth villages have in supporting underprivileged adolescents in acquiring basic skills for adult life and suggest guidelines as to which sub-groups and in which area programs should be developed.