Alternative models for species replacement of pelagic fishes

Summary It is well known that the stock abundance of a pelagic fish usually fluctuates and a species of pelagic fish which was dominant in abundance is often taken over by another species. Several alternative models for species replacement among pelagic fishes are presented and analyzed: (A) environmental fluctuation, (B) strong density-dependent reproduction rate, (C) a two-species system with phase variation (density-dependent change of life history traits), (D) a two-species competition system with environmental fluctuation, (E) cyclic advantage relationship among three competitive species, and (F) a two-prey, one-predator system. Different model requires different number of species for the occurrence of species replacement. Three criteria to test each hypothesis from qualitative properties of species replacement are proposed. Possible management policies to decrease the amplitude of stock fluctuations are discussed. As a result, if the catching effort to mackerels which is rare now is large, or if the catching effort to the sardine is still large when it begins to decline in stock abundance, fisheries may be strong destabilizing effect on the stock abundance.     

Marital status and psychiatric disorders among blacks and whites.

This paper examines the association between marital status and psychiatric disorder for Blacks and explores the extent to which these patterns differ from those for Whites. Widowed and separated/divorced Black males and females have higher rates of disorder than the married; never-married Blacks do not have an elevated risk of psychiatric illness. The association between marital status and disorder for White males is similar and stronger than that observed for Blacks. For White women, the separated/divorced have a higher risk of disorder than the married, and unmarried White females have higher rates of the substance abuse disorders, but lower rates of the anxiety disorder than the married. Across all marital status groups, Black males and White males have higher rates of disorder (except for depression), than females. A complex pattern emerges when gender differences in the relative rates of disorder for unmarried Blacks compared to married Blacks are considered. Separated/divorced Black men, widowed Black women, and never-married Black men are worse off than their respective peers. Except for the separated/divorced, opposite patterns are evident for Whites. Directions for further research are outlined.     

Marital Processes and Parental Socialization in Families of Color: A Decade Review of Research

Research published during the past decade on African American, Latino, and Asian American families is reviewed. Emphasis is given to selected issues within the broad domains of marriage and parenting. The first section highlights demographic trends in family formation and family structure and factors that contributed to secular changes in family structure among African Americans. In the second section, new conceptualizations of marital relations within Latino families are discussed, along with research documenting the complexities in African American men's conceptions of manhood. Studies examining within‐group variation in marital conflict and racial and ethnic differences in division of household labor, marital relations, and children's adjustment to marital and family conflict also are reviewed. The third section gives attention to research on (a) paternal involvement among fathers of color; (b) the relation of parenting behavior to race and ethnicity, grandmother involvement, neighborhood and peer characteristics, and immigration; and (c) racial and ethnic socialization. The article concludes with an overview of recent advances in the study of families of color and important challenges and issues that represent research opportunities for the new decade.     

Phenotypic Bias and Ethnic Identity in Filipino Americans*

Objective. Links between phenotypes (skin tone, physical features) and a range of outcomes (income, physical health, psychological distress) were examined. Ethnic identity was examined as a protective moderator of phenotypic bias. Method. Data were from a community sample of 2,092 Filipino adults in San Francisco and Honolulu. Results. After controlling for age, nativity, marital status, and education, darker skin was associated with lower income and lower physical health for females and males. For females, more ethnic features were associated with lower income. For males, darker skin was related to lower psychological distress. One interaction was found such that females with more ethnic features exhibited lower distress; however, ethnic identity moderated distress levels of those with less ethnic features. Conclusions. Phenotypic bias appears prevalent in Filipino Americans though specific effects vary by gender and skin color versus physical features. Discussion centers on the social importance of appearance and potential strengths gained from ethnic identification.     

Multivariate Stochastic Volatility Model With Realized Volatilities and Pairwise Realized Correlations

Abstract

Although stochastic volatility and GARCH (generalized autoregressive conditional heteroscedasticity) models have successfully described the volatility dynamics of univariate asset returns, extending them to the multivariate models with dynamic correlations has been difficult due to several major problems. First, there are too many parameters to estimate if available data are only daily returns, which results in unstable estimates. One solution to this problem is to incorporate additional observations based on intraday asset returns, such as realized covariances. Second, since multivariate asset returns are not synchronously traded, we have to use the largest time intervals such that all asset returns are observed to compute the realized covariance matrices. However, in this study, we fail to make full use of the available intraday informations when there are less frequently traded assets. Third, it is not straightforward to guarantee that the estimated (and the realized) covariance matrices are positive definite.

Our contributions are the following: (1) we obtain the stable parameter estimates for the dynamic correlation models using the realized measures, (2) we make full use of intraday informations by using pairwise realized correlations, (3) the covariance matrices are guaranteed to be positive definite, (4) we avoid the arbitrariness of the ordering of asset returns, (5) we propose the flexible correlation structure model (e.g., such as setting some correlations to be zero if necessary), and (6) the parsimonious specification for the leverage effect is proposed. Our proposed models are applied to the daily returns of nine U.S. stocks with their realized volatilities and pairwise realized correlations and are shown to outperform the existing models with respect to portfolio performances.     

LOSS OF INFORMATION ASSOCIATED WITH THE ORDER STATISTICS AND RELATED ESTIMATORS IN THE DOUBLE EXPONENTIAL DISTRIBUTION CASE

Fisher (1934) derived the loss of information of the maximum likelihood estimator (MLE) of the location parameter in the case of the double exponential distribution. Takeuchi & Akahira (1976) showed that the MLE is not second order asymptotically efficient. This paper extends these results by obtaining the (asymptotic) losses of information of order statistics and related estimators, and by comparing them via their asymptotic distributions up to the second order.