A likelihood ratio test for completed sampling in population size estimation studies

We propose a likelihood ratio test to assess that sampling has been completed in closed population size estimation studies. More precisely, we assess if the expected number of subjects that have never been sampled is below a user-specified threshold. The likelihood ratio test statistic has a nonstandard distribution under the null hypothesis. Critical values can be easily approximated and tabulated, and they do not depend on model specification. We illustrate in a simulation study and three real data examples, one of which involves ascertainment bias of amyotrophic lateral sclerosis in Gulf War veterans.     

Hypothetical role of men's sexual activity in the regulation of human sex ratio: Analysis of the sex ratio of post-war abandoned children

The regulation of the sex ratio at birth in human species remains poorly understood. After wars, a shift of the sex ratio in favor of men is always observed. Among the different hypothesis to explain this observation, one is to consider that Y-bearing spermatozoids have a weight advantage following insemination and that X-bearing spermatozoids, heavier, are more time-resistant. Following these observations, frequent sex may favor the birth of boys, whether infrequent sex may favor the birth of girls.Sustaining this sperm weight hypothesis, I report here that in France, after the two world wars, there has been an increase of abandoned illegitimate children with a significant shift of the sex ratio in favor of men. These observations may reflect an increase in illegitimate birth and indirectly an increase of men paternity.     

The time of a conscious sensory experience and mind-brain theories

Libet et al. and Popper & Eccles have the view that some single hypothesis about the time of a conscious sensory experience has certain consequences for various mind-brain theories. The view involves a fundamental inconsistency, which may cast doubt on experimental findings, and two hypotheses rather than one. The preferable hypothesis is doubtful. The preferable hypothesis has been thought to have mind-brain consequences principally because it has not been distinguished from a different hypothesis. The preferable hypothesis in fact does not have the supposed mind-brain consequences. The different hypothesis, which in fact does have the given consequences, is entirely unacceptable.     

Hormonal control of sex ratio

It has been hypothesized that the maternal gonadotrophin level at the time of conception is causally related to the sex of the resultant human zygote, high levels of hormone being associated with the production of female offspring. In this note, evidence for and against this hypothesis is reviewed. There seems so much evidence in its favour that one might conclude that it contains at least a kernel of truth. It is suggested here that of the components of gonadotrophin, the active one in this hypothesized sex-selective process is luteinizing hormone, rather than follicle-stimulating hormone. The hypothesis is nevertheless unable to accommodate several well-established sets of data. Accordingly it is suggested that other hormones, oestrogen and testosterone, have sex-selective properties too, high levels being associated with male offspring. This elaboration of the hypothesis, if it were true, would explain most, if not all, of the epidemiological data on the human secondary sex ratio. In particular it would explain Guerrero's data which have hitherto resisted explanation of any kind. No suggestion is made about possible mechanisms underlying these hypothesized sex-selective properties. But it seems that sex-selective abortion is not the only one. It is hoped that other workers may be stimulated not only to test the hypothesis as outlined here, but--if it survives this testing--to suggest such mechanisms.     

Relationship between functional diversity and productivity in meadow and marsh plant communities

功能多样性-生产力关系研究结果支持质量比假说和多样性假说, 但对于这两种假说的适用条件尚有争议。通过对吉林省西部草甸和沼泽植物群落的地上生物量、2个物种多样性指标(物种丰富度和Shannon-Weaver指数)、7种植物性状的两类功能多样性指标(群落权重均值和Rao二次熵), 以及土壤环境因子进行调查测量, 研究了群落功能多样性与生产力的关系。结果表明: 1)功能多样性与生产力的关系比物种多样性与生产力的关系更为密切; 2)功能群落权重均值解释生产力变异的能力好于Rao二次熵, 即优势物种对群落生产力的影响作用更大; 3)水淹条件影响着功能多样性与生产力的关系, 以群落权重均值为基础的质量比假说适于解释草甸群落功能多样性与生产力的关系, 而以Rao二次熵为基础的多样性假说适于解释有强烈环境筛(水淹)的沼泽群落功能多样性与生产力的关系。     

草甸和沼泽植物群落功能多样性与生产力的关系

功能多样性-生产力关系研究结果支持质量比假说和多样性假说, 但对于这两种假说的适用条件尚有争议。通过对吉林省西部草甸和沼泽植物群落的地上生物量、2个物种多样性指标(物种丰富度和Shannon-Weaver指数)、7种植物性状的两类功能多样性指标(群落权重均值和Rao二次熵), 以及土壤环境因子进行调查测量, 研究了群落功能多样性与生产力的关系。结果表明: 1)功能多样性与生产力的关系比物种多样性与生产力的关系更为密切; 2)功能群落权重均值解释生产力变异的能力好于Rao二次熵, 即优势物种对群落生产力的影响作用更大; 3)水淹条件影响着功能多样性与生产力的关系, 以群落权重均值为基础的质量比假说适于解释草甸群落功能多样性与生产力的关系, 而以Rao二次熵为基础的多样性假说适于解释有强烈环境筛(水淹)的沼泽群落功能多样性与生产力的关系。     

Ergot drugs and central monoaminergic mechanisms: a histochemical, biochemical and behavioral analysis.

The effects of ergot drugs on central monoaminergic mechanisms, particularly dopaminergic mechanisms, have been investigated in histochemical, biochemical and behavioral studies. It is concluded that the behavioral effects and the antiparkinsonian properties of ergot drugs can to a large extent be explained by the hypothesis that ergot drugs act at various dopamine receptor sites in the brain as partial agonists, the ratio of agonist-antagonist activity varying from one dopamine receptor population to another.     

Tests of Bivariate Symmetry with a One-sided Alternative in the Analysis of Variance

We consider a two-factor experiment in which the factors have the same number of levels with a natural ordering among levels. We test the hypothesis that the effects of the two treatments are symmetric against a one-sided alternative using the likelihood ratio criteria. Test of the one-sided alternative as a null hypothesis against no restriction has also been studied. Exact distribution theory under the null hypothesis is derived and is shown to be a weighted mixture of chi-square distributions. An example is used to illustrate the procedure.     

A statistical analysis of the effect of warfare on the human secondary sex ratio

Many factors have been hypothesized to affect the human secondary sex ratio (the annual percentage of males among all live births), among them race, parental ages, and birth order. Some authors have even proposed warfare as a factor influencing live birth sex ratios. The hypothesis that during and shortly after periods of war the human secondary sex ratio is higher has received little statistical treatment. In this paper we evaluate the war hypothesis using 3 statistical methods: linear regression, randomization, and time-series analysis. Live birth data from 10 different countries were included. Although we cannot speak of a general phenomenon, statistical evidence for an association between warfare and live birth sex ratio was found for several countries. Regression and randomization test results were in agreement. Time-series analysis showed that most human sex-ratio time series can be described by a common model. The results obtained using intervention models differed somewhat from results obtained by regression methods.     

Permutation tests for random effects in linear mixed models

Inference regarding the inclusion or exclusion of random effects in linear mixed models is challenging because the variance components are located on the boundary of their parameter space under the usual null hypothesis. As a result, the asymptotic null distribution of the Wald, score, and likelihood ratio tests will not have the typical χ(2) distribution. Although it has been proved that the correct asymptotic distribution is a mixture of χ(2) distributions, the appropriate mixture distribution is rather cumbersome and nonintuitive when the null and alternative hypotheses differ by more than one random effect. As alternatives, we present two permutation tests, one that is based on the best linear unbiased predictors and one that is based on the restricted likelihood ratio test statistic. Both methods involve weighted residuals, with the weights determined by the among- and within-subject variance components. The null permutation distributions of our statistics are computed by permuting the residuals both within and among subjects and are valid both asymptotically and in small samples. We examine the size and power of our tests via simulation under a variety of settings and apply our test to a published data set of chronic myelogenous leukemia patients.     

A Likelihood Ratio Test for the Nonparametric Behrens‐Fisher Problem

The nonparametric Behrens‐Fisher hypothesis is the most appropriate null hypothesis for the two‐sample comparison when one does not wish to make restrictive assumptions about possible distributions. In this paper, a numerical approach is described by which the likelihood ratio test can be calculated for the nonparametric Behrens‐Fisher problem. The approach taken here effectively reduces the number of parameters in the score equations to one by using a recursive formula for the remaining parameters. The resulting single dimensional problem can be solved numerically. The power of the likelihood ratio test is compared by simulation to that of a generalized Wilcoxon test of Brunner and Munzel. The tests have similar power for all alternatives considered when a simulated null distribution is used to generate cutoff values for the tests. The methods are illustrated on data on shoulder pain from a clinical trial.     

Extra cytoproct mutant in Paramecium tetraurelia: morphogenetical analysis of proters and opisthes.

To account for the differences between proters and opisthes with regard to extra cytoproct morphogenesis in Paramecium tetraurelia, two hypotheses have been proposed and tested. (i) The differences may be a result of different actions of proter-macronucleus and opisthe-macronucleus. This hypothesis has been tested by cytoplasmically connecting the proter with the opisthe in the form of chains, some of which have only one macronucleus per chain. However, the connected proters and opisthes remain different in extra cytoproct morphogenesis, thus arguing against the hypothesis. (ii) The differences may be a result of differences between the proter and the opisthe with regard to the development of their posterior-ventral cortex: proters have a newly-developed posterior-ventral cortex whereas opisthes receive the posterior-ventral cortex from the pre-fission mother animal. This hypothesis has been tested by surgically producing an opisthe with a newly-regenerated posterior cortex. Such opisthes, however, remain different from proters in extra cytoproct morphogenesis. Thus no direct support for the second hypothesis is obtained. Also, proter-opisthe difference in morphogenesis may be understood in terms of Wolpert's positional information hypothesis, by assuming that the anterior and posterior ends of a dividing animal serve as reference points for establishing a gradient and that positional information before separation of the two daughter animals leads to differences in extra cytoproct morphogenesis between them after separation.     

Mechanism of D-cycloserine action: alanine racemase from Escherichia coli W

The antibiotic d-cycloserine is an effective inhibitor of alanine racemase. The lack of inhibition by l-cycloserine of alanine racemase from Staphylococcus aureus led Roze and Strominger to formulate the cycloserine hypothesis. This hypothesis states that d-cycloserine has the conformation required of the substrates on the enzyme surface and that l-cycloserine cannot have this conformation. Alanine racemase from Escherichia coli W has been examined to establish whether these observations are a general feature of all alanine racemases. The enzyme (molecular weight = 95,000) has Michaelis-Menten constants of 4.6 x 10(-4)m and 9.7 x 10(-4)m for d- and l-alanine, respectively. The ratio of V(max) in the d- to l-direction is 2.3. The equilibrium constant calculated from the Haldane relationship is 1.11 +/- 0.15. Both d- and l-cycloserine are competitive inhibitors with constants (K(i)) of 6.5 x 10(-4)m and 2.1 x 10(-3)m, respectively. The ratio of K(m)d-alanine to K(i)d-cycloserine is 0.71, and the ratio of K(m)l-alanine to K(i)l-cycloserine is 0.46. Since l-cycloserine is an effective inhibitor, it is concluded that the cycloserine hypothesis does not apply to the enzyme from E. coli W.     

The DNA database search controversy revisited: bridging the Bayesian-frequentist gap

Two different quantities have been suggested for quantification of evidence in cases where a suspect is found by a search through a database of DNA profiles. The likelihood ratio, typically motivated from a Bayesian setting, is preferred by most experts in the field. The so-called np rule has been suggested through frequentist arguments and has been suggested by the American National Research Council and Stockmarr (1999, Biometrics55, 671-677). The two quantities differ substantially and have given rise to the DNA database search controversy. Although several authors have criticized the different approaches, a full explanation of why these differences appear is still lacking. In this article we show that a P-value in a frequentist hypothesis setting is approximately equal to the result of the np rule. We argue, however, that a more reasonable procedure in this case is to use conditional testing, in which case a P-value directly related to posterior probabilities and the likelihood ratio is obtained. This way of viewing the problem bridges the gap between the Bayesian and frequentist approaches. At the same time it indicates that the np rule should not be used to quantify evidence.     

Sectorial mosaics in the domestic pigeion: 25 more years.

The hypothesis of bipaternity--incorporation of tissue derived from supernumerary sperms into an embryo--to explain the origin of sectorial mosaicism in pigeons was advanced in 1949. Since then, 182 additional examples have come to my attention. Only one was reported to be a gynandromorph; sex ratios generally have been near 1 : 1. No environmental variable has shown significant relation to the origin of the mosaics, and only a slight familial tendency has been indicated. At least 15 color and pattern mutants have been involved, usually contrasting only two alleles. The frequency and its use in crosses. Complex mosaics, involving two or more loci in the contrasts numbered at least 38 cases, of which 11 are examined in more detail, and 6 shown in photographs. Several instances of germinal as well as somatic mosaicism were demonstrated by progeny tests. The bipaternity hypothesis has not been ruled out by evidence in any case.     

Secondary sex ratio and maternal dominance rank among wild yellow baboons (Papio cynocephalus) of Mikumi National Park,Tanzania

The Trivers and Willard model predicts that offspring of dominant mothers will be biased toward males and offspring of subordinate mothers towards females, whereas a local-resource-competition hypothesis predicts the reverse. Available data bearing upon these alternative predictions are inconsistent. It has been suggested that the local-resource-competition hypothesis will predominate when resources are scarce, and the Trivers-Willard hypothesis when resources are abundant. The relationship between maternal dominance and secondary sex ratio for 214 offspring of 61 females was examined using four troops of wild yellow baboons living in Mikumi National Park, where the population was increasing in a resource-rich habitat. For all troops combined, no significant relationship was found between offspring sex ratio and maternal rank. The four troops separately showed inconsistent trends, and in no case did the relationship reach conventional levels of statistical significance. In contrast, the local resource-competition hypothesis was supported by a study of yellow baboons done with one troop and 80 offspring in Amboseli National Park, where a massive population decline had occurred. The contrasting Amboseli and Mikumi results may be due to differences in resource-competition at the two study sites, or to stochastic variation. © 1992 Wiley-Liss, Inc.     

Do females adjust the sex of their offspring in relation to the breeding sex ratio?

When the adult sex ratio differs between years in local populations, but still is predictable between adjacent years, it has been proposed that the best strategy would be to bias the offspring sex ratio in favour of the rare sex. We tested this hypothesis using a data set of great reed warbler offspring, sexed by molecular techniques, that were collected over 11 breeding seasons at two adjacent reed marshes. Three important assumptions for this hypothesis are fulfilled in the studied great reed warbler population. First, a substantial proportion of great reed warblers are living in small local populations where sex ratio distortions would be sufficiently large and common. Second, breeding adults and their offspring return to breed in the local population to a high degree. Third, females have a possibility to assess the breeding sex ratio before laying their eggs. At our study site, the breeding sex ratio was positively correlated between successive years. However, contrary to our prediction, female great reed warblers seemed not to adjust their offspring sex ratio in relation to the local breeding sex ratio.     

No evidence for the 'expensive-tissue hypothesis' from an intraspecific study in a highly variable species

The 'expensive-tissue hypothesis' states that investment in one metabolically costly tissue necessitates decreased investment in other tissues and has been one of the keystone concepts used in studying the evolution of metabolically expensive tissues. The trade-offs expected under this hypothesis have been investigated in comparative studies in a number of clades, yet support for the hypothesis is mixed. Nevertheless, the expensive-tissue hypothesis has been used to explain everything from the evolution of the human brain to patterns of reproductive investment in bats. The ambiguous support for the hypothesis may be due to interspecific differences in selection, which could lead to spurious results both positive and negative. To control for this, we conduct a study of trade-offs within a single species, Thalassoma bifasciatum, a coral reef fish that exhibits more intraspecific variation in a single tissue (testes) than is seen across many of the clades previously analysed in studies of tissue investment. This constitutes a robust test of the constraints posited under the expensive-tissue hypothesis that is not affected by many of the factors that may confound interspecific studies. However, we find no evidence of trade-offs between investment in testes and investment in liver or brain, which are typically considered to be metabolically expensive. Our results demonstrate that the frequent rejection of the expensive-tissue hypothesis may not be an artefact of interspecific differences in selection and suggests that organisms may be capable of compensating for substantial changes in tissue investment without sacrificing mass in other expensive tissues.     

Hemispheric asymmetries in cortical electrical activity during sleep. I

The hypothesis of a predominance of the right hemisphere in stage REM as compared to NREM has been tested through a spectral analysis of the EEG recorded from left (T3) and right (T4) temporal sites in 5 young healthy right-handed male subjects. Variations in the asymmetry coefficient R - L/R + L in different sleep stages have been analyzed by one way ANOVAs and Sheffé's tests. The hypothesis of a progressive increase in left hemisphere activity throughout different REM cycles as one approaches final awakenings have been investigated by comparing variations in the asymmetry coefficient for epochs of REM and stage 2 NREM sampled in different phases of the REM cycle. EEG results do not support either the hypothesized stage dependent or cycle dependent variation in EEG activity during sleep. We question whether variations in EEG amplitude and synchronization can be used as indices of hemispheric asymmetries during sleep.     

Sex ratio variation in Iberian pigs

Within the area of sex allocation, one of the topics that has attracted a lot of attention is the sex ratio problem. Fisher (1930) proposed that equal numbers of males and females have been promoted by natural selection and it has an adaptive significance. But the empirical success of Fisher's theory remains doubtful because a sex ratio of 0.50 is also expected from the chromosomal mechanism of sex determination. Another way of approaching the subject is to consider that Fisher's argument relies on the underlying assumption that offspring inherit their parent's tendency in biased sex ratio and therefore that genetic variance for this trait exists. Here, we analyzed sex ratio data of 56,807 piglets coming from 550 boars and 1893 dams. In addition to classical analysis of heterogeneity we performed analyses fitting linear and threshold animal models in a Bayesian framework using Gibbs sampling techniques. The marginal posterior mean of heritability was 2.63 x 10(-4) under the sire linear model and 9.17 x 10(-4) under the sire threshold model. The probability of the hypothesis p(h(2) = 0) fitting the last model was 0.996. Also, we did not detect any trend in sex ratio related to maternal age. From an evolutionary point of view, the chromosomal sex determination acts as a constraint that precludes control of offspring sex ratio in vertebrates and it should be included in the general theory of sex allocation. From a practical view that means that the sex ratio in domestic species is hardly susceptible to modification by artificial selection.