Lynn Roy LaMotte

An Exact Test for the Presence of Random Walk Coefficients in a Linear Regression Model

Abstract Exact tests of the hypothesis that the mean vector of an observed T-variate random variable follows a conventional fixed-coefficient linear model, against the alternative that the regression parameters vary according to a first-order Markov process, are derived. Power functions of the tests are investigated in order to provide means of choosing a test.

A Simple 'Synthesis'-Based Method of Variance Component Estimation.

Abstract : An evaluation is attempted of the ever growing methodology in the estimation of variance components. Optimality properties are sometimes achieved at considerable computational efforts. Certain methods depend on a subjective ordering of the components, and if the ordering is unfortunate the method may fail to yield estimates for certain components while with a different ordering all components may well be estimable. The work involved in attempting all possible orderings of the variance components is usually prohibitive. The present method achieves optimality properties and is nevertheless computationally simple. In fact it possesses Minque optimality for a particular choice of norm, but also various other optimality properties and necessary and sufficient conditions for estimability associated with Minque simplify considerably. Moreover we are able to derive sufficient conditions for consistency which also provide estimability conditions of a simpler structure. The consistency of our estimators makes them convenient as starting points for a single ML cycle to obtain asymptotically fully efficient estimates.

Invariant Quadratic Estimators in the Random, One-Way ANOVA Model

There are no uniformly best invariant quadratic estimators of the variance components in the random, one-way ANOVA model. In the balanced model the ANOVA estimators are best among unbiased estimators, but are inadmissible among all invariant quadratic estimators. Two classes of admissible invariant quadratic estimators are presented in this paper: unbiased estimators which have minimum average variance over a prior distribution on the variance components and biased estimators which have minimum average mean squared-error.

Estimating Maggot Age from Weight Using Inverse Prediction

Forensic entomological evidence is most often used to estimate the postmortem interval (PMI). Satisfactory techniques have not been available to quantify the precision of such a PMI estimate. For Cochliomyia macellaria (F.) (Diptera: Calliphoridae), we describe construction of a confidence interval on age of a larva, given its weight. The method requires a controlled experiment by which weights of larvae are observed at ages spread over sufficient range to cover the time from egg hatch up to postfeeding stage. A statistical model relating distributions of weights to age is formulated and fit to these data. We assumed a simple model in which both means and variances of weight distributions are linearly interpolated between sampled ages. The weight of a larva of unknown age is then compared to the fitted model via inverse prediction to compute the confidence interval on age of the larva.

Social Engagement and Health in Younger, Older, and Oldest-Old Adults in the Louisiana Healthy Aging Study

Social support has been shown to influence health outcomes in later life. In this study, we focus on social engagement as an umbrella construct that covers select social behaviors in a life span sample that included oldest-old adults, a segment of the adult population for whom very little data currently exist. We examined relationships among social engagement, positive health behaviors, and physical health to provide new evidence that addresses gaps in the extant literature concerning social engagement and healthy aging in very old adults. Participants were younger (21-59 years), older (60-89 years), and oldest-old (90-97 years) adults (N = 364) in the Louisiana Healthy Aging Study (LHAS). Linear regression analyses indicated that age, gender, and hours spent outside of the house were significantly associated with self-reported health. The number of clubs and hours outside of home were more important factors in the analyses of objective health status than positive health behaviors, after considering age group and education level. These data strongly suggest that social engagement remains an important determinant of physical health into very late adulthood. The discussion focuses on practical applications of these results including social support interventions to maintain or improve late-life health.

p-values for postmortem intervals from arthropod succession data.

Two approaches, one based on the likelihood-ratio statistic and the other based on unconditioning Fishers exact test, are examined for obtaining a p-value in the comparison of the combination of arthropod species present on a mystery carcass to the observed frequency distribution of species combinations on carcasses exposed to the elements for a

Acute Alcohol Intoxication Impairs the Hematopoietic Precursor Cell Response to Pneumococcal Pneumonia

BACKGROUND Alcohol abuse is associated with an increased incidence and severity of pneumonia. In both the general population and individuals consuming excess alcohol, Streptococcus pneumoniae is the most frequent lung infection pathogen. Alcoholic patients with pneumonia frequently present with granulocytopenia, which is predictive of increased mortality. The mechanisms underlying this impaired granulopoietic response to pneumococcal pneumonia have yet to be elucidated. METHODS Acute alcohol intoxication was induced in mice 30 minutes before intrapulmonary infection with S. pneumoniae. Bone marrow, lung, and blood samples were collected. Bone marrow cells were also isolated from naïve mice and treated in vitro with plasma from mice infected with S. pneumoniae. RESULTS Alcohol intoxication impaired the pneumococcal-induced increase in granulocyte recruitment into the alveolar space, decreased bacterial clearance from the lung, and increased mortality. Pneumococcal pneumonia significantly increased bone marrow lineage(-) c-Kit(+) Sca-1(+) (LKS) cell number and colony-forming unit-granulocytes and monocyte (CFU-GM) activity of these cells. Both enhanced proliferation of LKS cells and re-expression of Sca-1 surface protein on downstream progenitor cells bearing lineage(-) c-Kit(+) Sca-1(-) surface markers accounted for the expansion of marrow LSK cells during pneumonia. Alcohol intoxication impaired these 2 mechanisms of LKS cell population expansion and was associated with a relative granulocytopenia during pneumococcal lung infection. CONCLUSIONS Alcohol inhibits the hematopoietic precursor cell response to pneumonia, which may serve as a mechanism underlying the granulocytopenia and impaired host defense in alcohol abusers with bacterial pneumonia.

Confidence intervals and tests on the variance ratio in random models with two variance components

The LM test is modified to test any value of the ratio of two variance components in a mixed effects linear model with two variance components. The test is exact, so it can be used to construct exact confidence intervals on this ratio.Exact Neyman-Pearson (NP) tests on the variance ratio are described.Their powers provide attainable upper bounds on powers of tests on the variance ratio.Efficiencies of LM tests, which include ANOVA tests, and NP tests are compared for unbalanced, random, one-way ANOVA models.Confidence intervals corresponding to LM tests and NP tests are described.

Prediction intervals via consonance intervals

The general form of prediction intervals is presented as the set of realized values of the response variable that would not lead to rejection of the hypothesis of equal population means, an approach that emphasizes consonance of the hypothesis with the data rather than confidence that the interval will cover the as yet unrealized response.

A Note on the Role of Independence in t Statistics Constructed From Linear Statistics in Regression Models

Abstract Some Studentized linear estimates do not follow Students t distributions because the numerator and denominator are not independent. Recognized in residuals, the problem can occur in other contexts as well. A remedy is easily obtained by adding another predictor variable to the regression model that removes the shared degree of freedom.