Modeling heterogeneity for bivariate survival data by the Weibull distribution

We propose bivariate Weibull regression model with heterogeneity (frailty or random effect) which is generated by Weibull distribution. We assume that the bivariate survival data follow bivariate Weibull of Hanagal (Econ Qual Control 19:83–90, 2004). There are some interesting situations like survival times in genetic epidemiology, dental implants of patients and twin births (both monozygotic and dizygotic) where genetic behavior (which is unknown and random) of patients follows a known frailty distribution. These are the situations which motivate to study this particular model. We propose two-stage maximum likelihood estimation for hierarchical likelihood in the proposed model. We present a small simulation study to compare these estimates with the true value of the parameters and it is observed that these estimates are very close to the true values of the parameters.     

Extracting a revised labor supply theory from Becker's model of the household

Conflicting assumptions about labor supply behavior lie at the nexus of ideological and theoretical debates regarding the reality of involuntary unemployment, the efficacy of Keynesian macro-policy, and the appropriate nature of welfare policy. This can in part be attributed to the fact that orthodox theory is effectively predicated upon describing the behavior of individuals whose level of affluence enables them to voluntarily withhold their labor from the market. Ironically, a means of resolution appears if we extend Gary Becker's utility producing model of the household to recognize two latent behavioral concerns: (1) the ‘need’ of households for money income in order to produce utility, and (2) the presence of work activity in the home. The resulting generalized labor supply model extends Becker's analysis to explicitly encompass both the behavior of the affluent, and the behavior of the poor who need to work in order to sustain their existence.     

Symbols Build Communication and Thought: The Role of Gestures and Words in the Development of Engagement Skills and Social‐emotional Concepts during Toddlerhood

Social skills and symbol skills are positively associated in middle childhood, but the relation between these domains is less clear in newly verbal toddlers. Vygotsky proposed that symbols are both tools for interaction and mental tools for thought. Do symbols help even very young children build skills for interacting with and conceptualizing the social world? Longitudinal data from 108 children and mothers were collected when children were 14, 24, and 36 months. Children's gestures and words during mother–child interactions were used as symbol skill indicators to predict children's abilities to engage others and the number of social‐emotional concepts children portray during play. In a series of growth models, words had a stronger effect on engagement skills whereas early gesture use predicted later development of social‐emotional concepts. Therefore, even in early development, symbols serve as both communication tools and mental tools to construct understanding of the social‐emotional world.     

Exact likelihood inference for Laplace distribution based on Type-II censored samples

We develop exact inference for the location and scale parameters of the Laplace (double exponential) distribution based on their maximum likelihood estimators from a Type-II censored sample. Based on some pivotal quantities, exact confidence intervals and tests of hypotheses are constructed. Upon conditioning first on the number of observations that are below the population median, exact distributions of the pivotal quantities are expressed as mixtures of linear combinations and of ratios of linear combinations of standard exponential random variables, which facilitates the computation of quantiles of these pivotal quantities. Tables of quantiles are presented for the complete sample case.     

Deconstructing maternal sensitivity: Predictive relations to mother‐child attachment in home and laboratory settings

Despite the well‐documented importance of parental sensitivity for child development, there is a lack of consensus regarding how best to assess it. We investigated the factor structure of maternal caregiving behavior as assessed at 12 months by the Maternal Behavior Q‐Sort (Pederson & Moran) with 274 mother‐infant dyads. Subsequently, we examined associations between these empirically‐derived dimensions and child attachment, assessed in the home and laboratory (final N = 157). Three dimensions of maternal behavior were identified, corresponding fairly closely to Ainsworth's original scales. They were labeled Cooperation/Attunement, Positivity, and Accessibility/Availability. Only Cooperation/Attunement consistently predicted home‐based attachment at 15 months and 2 years, and at comparable strength to the overall sensitivity score, suggesting that this construct may be central to sensitivity. At 18 months, compared to their primarily secure counterparts, different types of laboratory‐assessed insecure attachment were associated with different patterns of maternal behavior. Mothers in avoidant relationships (n = 18) were low on Cooperation/Attunement and Accessibility/Availability, but fairly high on Positivity. Mothers of disorganized infants (n = 11) were Cooperative/Attuned but somewhat less Positive toward, and less Accessible/Available to, their infants. A multidimensional approach to parental behavior may facilitate the identification of parenting precursors of insecure parent‐child relationships.     

Differential fertility in Ontario. An application of factorial design to a demographic problem

This paper describes the use of a probability sample to survey differential fertility. 475 women were randomly selected from the 1941 Census of Canada to provide tests of the existence of five differentials: income, present age, age by marriage, schooling and distance from a city. The sample was limited to one province and to two contrasting values of each of the five differentials under study. Significant differences are found for the effective distance as well as for age at marriage and schooling. This is taken as signifying that the diffusion of the small-family pattern has a spatial dimension.     

Recent changes in FDA's good laboratory practice regulations

In the Federal Register of December 22, 1978, the Food and Drug Administration (FDA) published regulations which described Good Laboratory Practice for safety tests conducted on regulated products (Anonymous, 1978). The regulations, popularly known as GLPs, have become universally recognized as the basic criteria for the conduct of a valid safety test and for assuring the quality and integrity of the collected data. Along with the publication of the GLPs, FDA instituted a vigorous program of inspection of toxicology laboratories to determine the degree of adherence to the regulations. In 1984, based on inspectional findings which revealed that a large majority of toxicology laboratories were adhering to the GLPs, FDA published a proposal intended to reduce the burden of compliance with the regulations (Anonymous, 1984). The proposal outlined major changes in the provisions on quality assurance, protocol preparation, test and control article characterization, and retention of specimens and samples. The final order based on the proposal was published in the federal register of September 4, 1987 (Anonymous). The purpose of this communication is to describe the procedures used by FDA to develop the final order, to discuss certain major issues that arose during its development, and to answer several questions that have arisen subsequently.     

The Effects of Participation Rate on the Internal Reliability of Peer Nomination Measures

Although low participation rates have historically been considered problematic in peer nomination research, some researchers have recently argued that small proportions of participants can, in fact, provide adequate sociometric data. The current study used a classical measurement perspective to investigate the internal reliability (Cronbach's α) of peer nomination measures of acceptance, popularity, friendship, prosocial behavior, and overt aggression. Data from 642 participants attending 10 schools were resampled at different participation rates ranging from 5 percent to 100 percent of the original samples. Results indicated that (1) the association between participation rate and Cronbach's α was curvilinear across schools and variables; (2) collecting more data for a given variable (by using unlimited vs. limited nominations, or two vs. one items) was significantly related to higher internal reliability; and (3) certain variables (overt aggression, popularity) were more reliable than others (acceptance, friendship). Implications for future research were discussed.