A Note on Sufficient Conditions for Valid Unmodified t Testing in Correlation Analysis with Autocorrelated and Heteroscedastic Sample Data

Traditionally, sphericity (i.e., independence and homoscedasticity for raw data) is put forward as the condition to be satisfied by the variance–covariance matrix of at least one of the two observation vectors analyzed for correlation, for the unmodified t test of significance to be valid under the Gaussian and constant population mean assumptions. In this article, the author proves that the sphericity condition is too strong and a weaker (i.e., more general) sufficient condition for valid unmodified t testing in correlation analysis is circularity (i.e., independence and homoscedasticity after linear transformation by orthonormal contrasts), to be satisfied by the variance–covariance matrix of one of the two observation vectors. Two other conditions (i.e., compound symmetry for one of the two observation vectors; absence of correlation between the components of one observation vector, combined with a particular pattern of joint heteroscedasticity in the two observation vectors) are also considered and discussed. When both observation vectors possess the same variance–covariance matrix up to a positive multiplicative constant, the circularity condition is shown to be necessary and sufficient. “Observation vectors” may designate partial realizations of temporal or spatial stochastic processes as well as profile vectors of repeated measures. From the proof, it follows that an effective sample size appropriately defined can measure the discrepancy from the more general sufficient condition for valid unmodified t testing in correlation analysis with autocorrelated and heteroscedastic sample data. The proof is complemented by a simulation study. Finally, the differences between the role of the circularity condition in the correlation analysis and its role in the repeated measures ANOVA (i.e., where it was first introduced) are scrutinized, and the link between the circular variance–covariance structure and the centering of observations with respect to the sample mean is emphasized.     

Starting Values for EM Estimation of Latent Class Joint Model

Latent class model is one of the important latent variable methods for joint modeling longitudinal and survival data. Latent class joint model can handle underlying heterogeneous population, discover subpopulation structure, and incorporate correlated non normally distributed outcomes. The maximum likelihood estimates of parameters in latent class joint model are generally obtained by the EM algorithm. Finding the starting values is one of the major issues to implement the EM algorithm successfully. In this article, initial value formulas are provided, a simulation study is conducted to show that the proposed starting values perform very well, and two illustrative examples are presented.     

Confidence Intervals for Survival Probabilities: A Comparison Study

The confidence interval of the Kaplan–Meier estimate of the survival probability at a fixed time point is often constructed by the Greenwood formula. This normal approximation-based method can be looked as a Wald type confidence interval for a binomial proportion, the survival probability, using the “effective” sample size defined by Cutler and Ederer. Wald-type binomial confidence interval has been shown to perform poorly comparing to other methods. We choose three methods of binomial confidence intervals for the construction of confidence interval for survival probability: Wilson's method, Agresti–Coull's method, and higher-order asymptotic likelihood method. The methods of “effective” sample size proposed by Peto et al. and Dorey and Korn are also considered. The Greenwood formula is far from satisfactory, while confidence intervals based on the three methods of binomial proportion using Cutler and Ederer's “effective” sample size have much better performance.     

多元化决策主体在诉求表达实现机制中的功能分析

文章在阐释诉求表达实现机制概念的基础上,强调了该机制中决策主体的多元性,并进一步分析了多元化决策主体在诉求表达实现机制运行过程中,所发挥的尊重利益、承认差别、促进沟通、协调整合、客观可行和促进发展等六大功能。     

Measurement and determinants of efficiency in the municipal police service

The purpose of this paper is to analyze the efficiency of the police service in Spanish municipalities with a population of more than 50,000 inhabitants. Using Data Envelopment Analysis, we obtain the efficiency levels and the targets that the input and outputs have to reach to be efficient in the provision of the police service. Next, and based on the literature, the effect of the following environmental variables is verified: young population, number of foreigners, unemployment, municipal per capita income, tourist level of the municipality, and ideology and political strength of the municipal government. Findings show that an increase in the number of young people in the municipality means an improved efficiency in the local police service. In contrast, cultural diversity (measured by the percentage of foreigners in the total population), unemployment, the mayor's ideology and political fragmentation of government do not have a significant effect on the level of efficiency. On the other hand, higher municipal per capita income means less efficiency, while an increase in tourism activity is related to the improvement of this.     

Semiparametric inference for a general class of models for recurrent events

Procedures for estimating the parameters of the general class of semiparametric models for recurrent events proposed by Peña and Hollander [(2004). Models for recurrent events in reliability and survival analysis. In: Soyer R., Mazzuchi T., Singpurwalla N. (Eds.), Mathematical Reliability: An Expository Perspective. Kluwer Academic Publishers, Dordrecht, pp. 105–123 (Chapter 6)] are developed. This class of models incorporates an effective age function encoding the effect of changes after each event occurrence such as the impact of an intervention, it models the impact of accumulating event occurrences on the unit, it admits a link function in which the effect of possibly time-dependent covariates are incorporated, and it allows the incorporation of unobservable frailty components which induce dependencies among the inter-event times for each unit. The estimation procedures are semiparametric in that a baseline hazard function is nonparametrically specified. The sampling distribution properties of the estimators are examined through a simulation study, and the consequences of mis-specifying the model are analyzed. The results indicate that the flexibility of this general class of models provides a safeguard for analyzing recurrent event data, even data possibly arising from a frailty-less mechanism. The estimation procedures are applied to real data sets arising in the biomedical and public health settings, as well as from reliability and engineering situations. In particular, the procedures are applied to a data set pertaining to times to recurrence of bladder cancer and the results of the analysis are compared to those obtained using three methods of analyzing recurrent event data.     

Learning new behaviour patterns: a longitudinal test of Karasek's active learning hypothesis among Dutch teachers

This investigation deals with the active learning hypothesis in Karasek and Theorell's (1990) job demands-control model. The active learning hypothesis holds that high levels of learning and self-efficacy will occur among incumbents of high job demands/high job control jobs, whereas low levels of learning and self-efficacy will be found in low demands/low control jobs. This study tested these notions in the context of a two-wave study conducted over a period of one year among 876 Dutch teachers. Regression analysis revealed that job demands had a lagged negative (rather than a positive) effect on learning and self-efficacy; as expected, job control had a positive effect. Thus, the highest levels of learning and self-efficacy were found among incumbents of high control/low demands jobs (and not among incumbents of high control/high demands jobs). Further, the effects of changes in work characteristics on changes in learning behaviour and self-efficacy were examined, providing additional evidence that especially the transition from a low demands/low control to a high demands/low control job is associated with a strong deterioration of learning and self-efficacy. It is concluded that future research should address the interrelationships between learning and strain, preferably using longitudinal designs.     

Bargaining and Strategic Demand Commitment

On occasion, in multilateral negotiations, interested parties make unilateral demands. Certain agreements need unanimity. However, a lesser degree of consensus may be feasible. In this paper, an alternating demand bargaining game among n players is proposed, which envisages varying consensus requirements and commitment, both crucial in generating a unique and efficient outcome of the bargaining process.     

Evidence for the need to distinguish between self-initiated and organizationally imposed overload in studies of work stress

This study attempts to enhance our understanding of the inconsistencies reported in the literature concerning the relationship between work overload and work outcomes. We tested the proposition that work overload should be divided into two constructs based on its source: self-initiated overload (SIO), and organization-imposed overload (OIO). Based on the work stress and job crafting literatures, we expected that SIO and OIO would tend to relate differentially to the work outcomes of job satisfaction, emotional exhaustion, work–family conflict, job performance, and helping organizational citizenship behaviours. A study was conducted using three samples, the first consisting of full-time employed students in three countries (N?=?116), the second consisting of the nursing staffs of six private hospitals in Switzerland, and the third consisting of 161 middle manager–supervisor dyads in Switzerland. Two different measures of SIO and OIO were used. SIO was found to have a more beneficial relationship with the work outcomes than OIO, general supporting our hypothesis. Theoretical and practical implications are discussed.     

我国保险业有效供给能力研究

我国现有保险业的发展水平仍然很低，未来的增量空间巨大。未来增量空间所形成的巨大需求缺口亟需保险业提高自身供给能力来满足，而由于我国保险业有效供给能力低下，需要我们从完善市场结构等多方面来强化有效供给能力。