Jenny A. Baglivo

Headache in cerebrovascular disease.

Two hundred fifteen consecutive patients with cerebrovascular events were evaluated pro- spectively for the incidence and characteristics of headache. Of 163 patients able to communicate, headache occurred in 29% with bland infarcts, 57% with parenchymal hemorrhage, 36% with transient Lschemic attacks and 17% with lacunar infarcts. Patients with a history of recurrent throbbing headache were significantly more likely to have headache, usually throbbing in quality, during the present illness. Women developed headache significantly more often than men. Headache began prior to the vascular event in 60% of patients and at its onset in 25%. The quality, onset and duration of the headache varied widely among patients. Headache in cerebrovascular disease is common, though neither its occurrence nor characteristics predict lesion type or location. Though the pathogenesis of the headache is unknown, its association with prior throbbing headache suggests that similar factors may operate in both. Stroke Vol 15, No 6, 1984

Laboratory investigations of the effects of predator sex and size on prey selection by the Asian crab, Hemigrapsus sanguineus

Laboratory studies have shown that the nonindigenous Asian shore crab, Hemigrapsus sanguineus, readily consumes three species of commercial bivalves: blue mussels, Mytilus edulis, soft-shell clams, Mya arenaria, and oysters, Crassostrea virginica. Although crabs can eat bivalves of a wide size range, they preferred the smaller prey (</=10 mm SL). Prey critical size limits exist for M. edulis and C. virginica, but not M. arenaria, possibly because of differences in shell characteristics among the three species. Crabs preferred M. arenaria over both M. edulis and C. virginica, and M. edulis was strongly preferred over C. virginica in pairwise comparison tests. Experiments to determine feeding rates on mussels showed that H. sanguineus can consume large numbers of mussels daily (12.7+/-11.6 mussels day(-1); sexes pooled; N=59). Mussel consumption rates increased with size of the predator and male crabs consumed more mussels than did similarly sized female crabs. The high densities of Hemigrapsus that occur in the wild, their effectiveness as predators of juvenile bivalves and their large appetites suggest an important role for these predators in restructuring the prey communities in habitats into which they have been introduced.

LABORATORY INVESTIGATIONS OF FOOD SELECTION BY THE ASIAN SHORE CRAB, HEMIGRAPSUS SANGUINEUS: ALGAL VERSUS ANIMAL PREFERENCE

Abstract The Asian shore crab, Hemigrapsus sanguineus (De Haan, 1853), is an opportunistic omnivore with well-developed predatory tendencies and a strong preference for animal food items over algae. In laboratory experiments, 71 percent (319/448) of the crabs given a choice between macroalgae (Enteromorpha spp. and/or Chondrus crispus) and benthic invertebrates (Mytilus edulis and/or Semibalanus balanoides) consumed animals only. There were no significant differences in food preference between sexes or between juvenile and adult crabs. Relative abundance of food type, either algal or animal, in small food patches did not affect crab food preference. Crabs with prolonged starvation periods (5-d), however, consumed both food types more often than those that had been starved for 1-d only. Experiments to determine the effect of conspecifics on food selectivity showed that increased crab density leads to increased diet breadth, suggesting that competition for food can alter food selection patterns of H. sanguineus. Results reported here and in previous studies provide strong evidence that predation pressure exerted by H. sanguineus could play an important role in structuring the post-settlement population dynamics of its invertebrate prey, possibly leading to population declines of commercial shellfish, especially blue mussels.

Methods for Exact Goodness-of-Fit Tests

Abstract Numerous goodness-of-fit tests with asymptotic chi-squared distributions have been proposed for discrete multivariate data, and there has been much discussion about using asymptotic results for computing critical values when there are small expected cell values. Although exact methods would be preferred in these situations, it generally is believed that such methods are computationally intractable. We propose methods for calculating exact distributions and significance levels for goodness-of-fit statistics that are computationally feasible over a wide range of models. In particular, the distribution for a simple multinomial model can be evaluated in polynomial time. For composite null hypotheses, we calculate the distribution conditional on the sufficient statistics for the nuisance parameters. We calculate the characteristic function of a distribution and invert the characteristic function using the fast Fourier transform (FFT). Our approach emphasizes the relationship between exact methods and ...

AN EXPERIMENTAL FIELD STUDY OF SITE FIDELITY AND MOBILITY IN THE ASIAN SHORE CRAB, HEMIGRAPSUS SANGUINEUS

Abstract Experimental field studies at two sites in Long Island Sound have demonstrated that the nonindigenous Asian shore crab, Hemigrapsus sanguineus deHaan 1853, is a highly mobile grapsid crab that shows limited fidelity to a particular shelter or feeding site. Recovery rates of tagged crabs differed significantly at the two sites, but no differences in site fidelity were measurable between males and females at either site. Between-site differences in percent crabs recovered may be due to differences in food and shelter availability at the two sites. There is some suggestion that familiarity with a shelter site may influence site fidelity by leading to reduced mobility. A conservative estimate (based on recovered crabs only) of the mean distance traveled in 24 hours (n = 38) was 7.43 ± 1.54 m; among those crabs recovered a distance > 5 m from the release point (n = 15) the mean distance traveled was 16.87 ± 2.23 m. The rapid, widespread dispersal characteristic of the Asian crab invasion along the east coast of the United States may be due in part to the high adult mobility and low site fidelity exhibited by H. sanguineus.

Methods for the Analysis of Contingency Tables with Large and Small Cell Counts

Abstract The traditional practice has been to analyze contingency tables using asymptotic χ2 approximations for the tail probability of certain test statistics even when the approximation is known to be poor. For two-dimensional tables Pearsons X 2 statistic is most commonly used, whereas for multidimensional tables the likelihood ratio test is preferred because it makes it easy to test series of nested hypotheses. When asymptotic approximations are not adequate, exact tests are preferred. Recent advances in algorithms have broadened the range of two-dimensional tables for which satisfactory answers can be obtained (Baglivo, Olivier, and Pagano 1985; Mehta and Patel 1983, 1986; Pagano and Taylor-Halvorsen 1981). In this article we propose algorithms that use a mixture of exact and asymptotic techniques to calculate tail probabilities. Our methods can be used with several different test statistics for two-dimensional and multidimensional contingency-table models and hence further broaden the set of tables...

FIDDLER CRAB BURROW USAGE BY THE ASIAN CRAB, HEMIGRAPSUS SANGUINEUS, IN A LONG ISLAND SOUND SALT MARSH

Abstract The Asian shore crab, Hemigrapsus sanguineus, was observed occupying fiddler crab burrows (Uca pugnax) at low tide in a Spartina salt marsh at Sherwood Island, Westport, Connecticut. Forty-seven percent (48/103) of the fiddler crab burrows censused were occupied by crabs. Of those, 81% held fiddler crabs while the remainder held Asian crabs. Fiddler crabs and Asian crabs were never found in the same burrow. Unlike the Asian crab, fiddler crabs preferred areas of the “marsh edge” where rocks and small stones were not present. Hemigrapsus sanguineus, which can be found under the shelter of rocks, shells, and other debris on tidal flats along the fringes of the marsh, probably searches the marsh edge as the tide recedes for unused burrows to occupy. Field caging experiments used to investigate possible competitive interactions between these two species indicated that the presence of the Asian crab had no effect on burrow utilization by the fiddler crab. It is unlikely that patterns of habitat use by the east coast salt marsh fiddler crab, Uca pugnax, will be significantly affected by the recent introduction of the Asian crab, H. sanguineus, to this area.

Permutation Distributions via Generating Functions with Applications to Sensitivity Analysis of Discrete Data

Abstract Generating functions provide a simple and elegant way to describe probability or frequency distributions of discrete statistics and, in particular, permutation distributions. They are also a computational tool. Many efficient algorithms, including those described as fast Fourier transform methods, network methods, and multiple shift methods, are different implementations of the recursions needed to evaluate generating functions efficiently. Our goals here are twofold. First, we make the relationship between these efficient methods and generating functions explicit; this establishes a language for looking at other questions in randomization/exact inference and may help in finding more efficient implementations. Second, we propose methods to examine the sensitivity of results of exact analysis of discrete data to small perturbations in the data. Specifically, we consider two settings: how the analysis would change if one outcome changed, and how the analysis would change if one observation was adde...

An equivariant Wall obstruction theory

Let G be a finite group. For a certain class of CW-complexes with a G-action which are equivariantly dominated by a finite complex we define algebraic invariants to decide when the space is equivariantly homotopy or homology equivalent to a finite complex.

Analysis of discrete data: rerandomization methods and complexity

Analysis of discrete data, and especially contingency table data, plays a central role in biostatistics. Traditional methods rely on approximations based on asymptotic results which are very powerful but not always appropriate. In this article we show that efficient rerandomization methods may be developed for many commonly used models and tests: multinomial testing, specifically goodness-of-fit and max tests; and goodness-of-fit of log-linear models for contingency tables. The feasibility (complexity) of these algorithms is a function of the sufficient statistics for the models. By contrast, algorithms which require the explicit enumeration of all outcomes in the sample space are exponential in the degrees of freedom, and are usually not feasible except when sample sizes are unrealistically small. The algorithms we present are different from recently proposed methods since we show how to calculate permutation distributions of commonly used statistics rather than calculating p-values for exact tests, and we emphasize underlying probability formulas rather than implementation details.