Eine neue Methode zur Untersuchung von Mikroprozessen in Lerndyaden: Eine Videostudie unter Berücksichtigung von kognitiven Grundfähigkeiten und Zielorientierungen

The study at present uses a new video method with individual audio tracks to investigate micro processes within learning in a simulation based learning setting. Visible and listenable behaviour was coded with regard to peer tutoring and problem solving. The frequencies and durations of these categories were summarized and used as dependent variables in regression models with cognitive abilities and goal orientations as predictors. Results showed that variation in the dyadic interactional behaviour was systematically related to these properties of the partners. For example, while overt problem solving behaviour is related to goal orientations there was no such effect for the cognitive abilities. Implications for the composition of dyadic learning groups and for further video study arrangements applying the new method will be discussed.     

Likelihood Inference for a Fractionally Cointegrated Vector Autoregressive Model

We consider model based inference in a fractionally cointegrated (or cofractional) vector autoregressive model, based on the Gaussian likelihood conditional on initial values. We give conditions on the parameters such that the process X_t is fractional of order d and cofractional of order d−b; that is, there exist vectors β for which β^′X_t is fractional of order d−b and no other fractionality order is possible. For b=1, the model nests the I(d−1) vector autoregressive model. We define the statistical model by 0 < bd, but conduct inference when the true values satisfy 0d₀−b₀<1/2 and b₀≠1/2, for which β₀^′X_t is (asymptotically) a stationary process. Our main technical contribution is the proof of consistency of the maximum likelihood estimators. To this end, we prove weak convergence of the conditional likelihood as a continuous stochastic process in the parameters when errors are independent and identically distributed with suitable moment conditions and initial values are bounded. Because the limit is deterministic, this implies uniform convergence in probability of the conditional likelihood function. If the true value b₀>1/2, we prove that the limit distribution of is mixed Gaussian, while for the remaining parameters it is Gaussian. The limit distribution of the likelihood ratio test for cointegration rank is a functional of fractional Brownian motion of type II. If b₀<1/2, all limit distributions are Gaussian or chi‐squared. We derive similar results for the model with d = b, allowing for a constant term.     

Evaluating the performance of simple estimators for probit models with two dummy endogenous regressors

This study considers the small sample performance of approximate but simple two-stage estimators for probit models with two endogenous binary covariates. Monte Carlo simulations show that all the considered estimators, including the simulated maximum-likelihood (SML) estimation, of the trivariate probit model are biased in very small samples (N=100). With moderately small samples (N=500), some of the approximations perform as well as the SML estimator when the degree of endogeneity is not very large. Some of the approximations seem robust with higher correlations and are also promising for testing the exogeneity of binary covariates. The methods are used to estimate the impact of employment-based health insurance and health care (HC) on HC use, where the approximations seem to work at least as well as the SML and in some cases better.     

Finite Sample Comparison of Parametric,Semiparametric, and Wavelet Estimators of Fractional Integration

ABSTRACT

In this paper we compare through Monte Carlo simulations the finite sample properties of estimators of the fractional differencing parameter, d. This involves frequency domain, time domain, and wavelet based approaches, and we consider both parametric and semiparametric estimation methods. The estimators are briefly introduced and compared, and the criteria adopted for measuring finite sample performance are bias and root mean squared error. Most importantly, the simulations reveal that (1) the frequency domain maximum likelihood procedure is superior to the time domain parametric methods, (2) all the estimators are fairly robust to conditionally heteroscedastic errors, (3) the local polynomial Whittle and bias-reduced log-periodogram regression estimators are shown to be more robust to short-run dynamics than other semiparametric (frequency domain and wavelet) estimators and in some cases even outperform the time domain parametric methods, and (4) without sufficient trimming of scales the wavelet-based estimators are heavily biased.     

Issues in operationalizing and comparing leadership constructs

Numerous theories of leadership have yielded a rich array of leadership constructs, yet there has been little comparative work across theories. The authors of this letter exchange compare views around the definition of leadership and four issues related to operationalizing and comparing leadership constructs: the measurement of leadership constructs, overlaps in measures of leadership, follower's ability to differentiate among leadership constructs, and conceptualizing context in studying leadership.     

Segmented Assimilation,Local Context and Determinants of Drug Violence in Miami and San Diego: Does Ethnicity and Immigration Matter?1

Does the ethnic and immigrant composition of a community and existence of immigrant enclaves or barrios influence community level drug violence? This study explores the relationship between these and other factors in Miami and San Diego census tracts. We employ data about the distribution of Cubans, Central Americans, Haitians, Mexicans and Southeast Asians, controlling for social and economic influences of drug versus non‐drug violence. We also analyze the impact of various waves of immigration and immigrant communities to understand the circumstances under which drug violence occurs or is limited at the census tract level. The findings lend some support to the positive and negative aspects of Portes and Rumbaut's (2001) segmented assimilation hypothesis in Miami and San Diego neighborhoods. The strength of this conclusion varies and is contingent upon ethnic composition, new versus old immigration, and the all‐encompassing effects of economic deprivation     

Separating online scheduling algorithms with the relative worst order ratio

The relative worst order ratio is a measure for the quality of online algorithms. Unlike the competitive ratio, it compares algorithms directly without involving an optimal offline algorithm. The measure has been successfully applied to problems like paging and bin packing. In this paper, we apply it to machine scheduling. We show that for preemptive scheduling, the measure separates multiple pairs of algorithms which have the same competitive ratios; with the relative worst order ratio, the algorithm which is “intuitively better” is also provably better. Moreover, we show one such example for non-preemptive scheduling.     

L’évolution d’une règle d’organisation sur dix ans : l’accord collectif chez un constructeur d’automobiles en Allemagne

Based on ten years of research on the four-day workweek at Volkswagen in Germany, a longitudinal analysis is proposed of collective bargaining and the new forms of regulation that the automaker is putting into effect. Since the initial labor agreement worked out in 1993, organizational rules have changed considerably. The negotiated agreement on the reduction about the time spent working, the loss of wages and the number of jobs to be kept has been extended by increasing flexibility in the organization of work time. Under pressure from international competition, which has forced the firm to redesign its production process, the company is going to gradually reconfigure its internal labor market.