823 research outputs found
Valid Asymptotic Expansions for the Maximum Likelihood Estimator of the Parameter of a Stationary, Gaussian, Strongly Dependent Process
We establish the validity of an Edgeworth expansion to the distribution of the maximum likelihood estimator of the parameter of a stationary, Gaussian, strongly dependent process. The result covers ARFIMA type models, including fractional Gaussian noise. The method of proof consists of three main ingredients: (i) verification of a suitably modified version of Durbin's (1980) general conditions for the validity of the Edgeworth expansion to the joint density of the log-likelihood derivatives; (ii) appeal to a simple result of Skovgaard (1986) to obtain from this an Edgeworth expansion for the joint distribution of the log-likelihood derivatives; (iii) appeal to and extension of arguments of Bhattacharya and Ghosh (1978) to accomplish the passage from the result on the log-likelihood derivatives to the result for the maximum likelihood estimators. We develop and make extensive use of a uniform version of Dahlhaus's (1989) Theorem 5.1 on products of Toeplitz matrices; the extension of Dahlhaus's result is of interest in its own right. A small numerical study of the efficacy of the Edgeworth expansion is presented for the case of fractional Gaussian noise.Edgeworth expansions, long memory processes, ARFIMA models
Case-control survival analysis with a general semiparametric shared frailty model--a pseudo full likelihood approach
In this work we deal with correlated failure time (age at onset)
data arising from population-based case-control studies, where case
and control probands are selected by population-based sampling and
an array of risk factor measures is collected for both cases and con-
trols and their relatives. Parameters of interest are eĀ®ects of risk
factors on the failure time hazard function and within-family depen-
dencies among failure times after adjusting for the risk factors. Due
to the retrospective sampling scheme, large sample theory for existing
methods has not been established. We develop a novel technique for
estimating the parameters of interest under a general semiparamet-
ric shared frailty model. We also present a simple, easily computed,
and non-iterative nonparametric estimator for the cumulative base-
line hazard function. We provide rigorous large sample theory for the
proposed method. We also present simulation results and a real data
example for illustrating the utility of the proposed method
Valid Asymptotic Expansions for the Maximum Likelihood Estimator of the Parameter of a Stationary, Gaussian, Strongly Dependent Process
We establish the validity of an Edgeworth expansion to the distribution of the maximum likelihood estimator of the parameter of a stationary, Gaussian, strongly dependent process. The result covers ARFIMA type models, including fractional Gaussian noise. The method of proof consists of three main ingredients: (i) veriļ¬cation of a suitably modiļ¬ed version of Durbinās (1980) general conditions for the validity of the Edgeworth expansion to the joint density of the log-likelihood derivatives; (ii) appeal to a simple result of Skovgaard (1986) to obtain from this an Edgeworth expansion for the joint distribution of the log-likelihood derivatives; (iii) appeal to and extension of arguments of Bhattacharya and Ghosh (1978) to accomplish the passage from the result on the log-likelihood derivatives to the result for the maximum likelihood estimators. We develop and make extensive use of a uniform version of Dahlhausās (1989) Theorem~5.1 on products of Toeplitz matrices; the extension of Dahlhausās result is of interest in its own right. A small numerical study of the eļ¬icacy of the Edgeworth expansion is presented for the case of fractional Gaussian noise
Same-Sex Social Behavior in Meadow Voles: Multiple and Rapid Formation of Attachments
Adult meadow voles (Microtus pennsylvanicus) are solitary in the springāsummer reproductive season, but during winter months, females and males are socially tolerant and aggregate in groups. This behavioral difference is triggered by day length: female meadow voles housed in short, winterlike day lengths form same-sex partner preferences, whereas those housed in long, summer-like day lengths are less social. The present study demonstrates that same-sex social attachments in short day lengths are not exclusive; females formed concurrent attachments with more than one individual, and with non-kin as well as siblings. Partner preferences between females were established within one day of cohousing and did not intensify with greater durations of cohabitation. Males also formed same-sex social attachments, but unlike female affiliative behavior, male partner preferences were not significantly affected by day length. These data are discussed in the context of field behavior and the physiological mechanisms supporting social behavior in voles
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