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Population Mean (population + mean)
Selected AbstractsTesting a Partial Ordering of Population Means with Application to Inference about Growth Habits of Cowpea GenotypesBIOMETRICS, Issue 4 2007Daniel R. Jeske Summary Using general results available in the literature, we derive the likelihood ratio test for a particular partial ordering of means that naturally arises in a biological context. We then show that the conceptual and computational complexity of the derivation can be substantially reduced by equivalently deriving the test using the intersection-union principle for decomposing a complex null hypothesis into elemental forms. A Monte Carlo algorithm for obtaining the p -value of the test is proposed. The test procedure is illustrated with a data set of the competitive ability of several cowpea genotypes, where previous experiments have indicated the proposed partial order of the means. A simulation study is used to examine the power of the test. [source] The Child Health Questionnaire in Australia: reliability, validity and population meansAUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 2 2000Elizabeth Waters Objective: To provide reliability, validity and population means for the Australian Authorised Adaptation of the parent-report Child Health Questionnaire (CHQ). Method: We surveyed a representative sample of Australian parents of school-aged children (5,18 years) in Victoria between July and December 1997, using a school-based cluster sample design stratified by educational sector and age. Results: Some 5, 414 parents responded (72%). Good psychometric performance was observed for the CHQ in Australia. Population means demonstrated differences in health on domains of functioning and well-being by age and gender. This population-derived sample demonstrated high ceiling values on Physical Functioning and Social Role scales. Implications: The CHQ appears to be a reliable and valid measure of child and adolescent functional health and well-being for the Australian population. Child health outcomes of children and adolescents with particular conditions or within population subgroups can be compared with these age and gender benchmarks. Appropriate uses for the CHQ may be to discriminate between children who are generally healthy and children with health problems, or in population surveys partnered with measures that extend the range of physical functioning and social functioning. [source] Ratio estimators in adaptive cluster samplingENVIRONMETRICS, Issue 6 2007Arthur L. Dryver Abstract In most surveys data are collected on many items rather than just the one variable of primary interest. Making the most use of the information collected is a issue of both practical and theoretical interest. Ratio estimates for the population mean or total are often more efficient. Unfortunately, ratio estimation is straightforward with simple random sampling, but this is often not the case when more complicated sampling designs are used, such as adaptive cluster sampling. A serious concern with ratio estimates introduced with many complicated designs is lack of independence, a necessary assumption. In this article, we propose two new ratio estimators under adaptive cluster sampling, one of which is unbiased for adaptive cluster sampling designs. The efficiencies of the new estimators to existing unbiased estimators, which do not utilize the auxiliary information, for adaptive cluster sampling and the conventional ratio estimation under simple random sampling without replacement are compared in this article. Related result shows the proposed estimators can be considered as a robust alternative of the conventional ratio estimator, especially when the correlation between the variable of interest and the auxiliary variable is not high enough for the conventional ratio estimator to have satisfactory performance. Copyright © 2007 John Wiley & Sons, Ltd. [source] A cost analysis of ranked set sampling to estimate a population meanENVIRONMETRICS, Issue 3 2005Rebecca A. Buchanan Abstract Ranked set sampling (RSS) can be a useful environmental sampling method when measurement costs are high but ranking costs are low. RSS estimates of the population mean can have higher precision than estimates from a simple random sample (SRS) of the same size, leading to potentially lower sampling costs from RSS than from SRS for a given precision. However, RSS introduces ranking costs not present in SRS; these costs must be considered in determining whether RSS is cost effective. We use a simple cost model to determine the minimum ratio of measurement to ranking costs (cost ratio) necessary in order for RSS to be as cost effective as SRS for data from the normal, exponential, and lognormal distributions. We consider both equal and unequal RSS allocations and two types of estimators of the mean: the typical distribution-free (DF) estimator and the best linear unbiased estimator (BLUE). The minimum cost ratio necessary for RSS to be as cost effective as SRS depends on the underlying distribution of the data, as well as the allocation and type of estimator used. Most minimum necessary cost ratios are in the range of 1,6, and are lower for BLUEs than for DF estimators. The higher the prior knowledge of the distribution underlying the data, the lower the minimum necessary cost ratio and the more attractive RSS is over SRS. Copyright © 2005 John Wiley & Sons, Ltd. [source] Environmental power analysis , a new perspectiveENVIRONMETRICS, Issue 5 2001David R. Fox Abstract Power analysis and sample-size determination are related tools that have recently gained popularity in the environmental sciences. Their indiscriminate application, however, can lead to wildly misleading results. This is particularly true in environmental monitoring and assessment, where the quality and nature of data is such that the implicit assumptions underpinning power and sample-size calculations are difficult to justify. When the assumptions are reasonably met these statistical techniques provide researchers with an important capability for the allocation of scarce and expensive resources to detect putative impact or change. Conventional analyses are predicated on a general linear model and normal distribution theory with statistical tests of environmental impact couched in terms of changes in a population mean. While these are ,optimal' statistical tests (uniformly most powerful), they nevertheless pose considerable practical difficulties for the researcher. Compounding this difficulty is the subsequent analysis of the data and the impost of a decision framework that commences with an assumption of ,no effect'. This assumption is only discarded when the sample data indicate demonstrable evidence to the contrary. The alternative (,green') view is that any anthropogenic activity has an impact on the environment and therefore a more realistic initial position is to assume that the environment is already impacted. In this article we examine these issues and provide a re-formulation of conventional mean-based hypotheses in terms of population percentiles. Prior information or belief concerning the probability of exceeding a criterion is incorporated into the power analysis using a Bayesian approach. Finally, a new statistic is introduced which attempts to balance the overall power regardless of the decision framework adopted. Copyright © 2001 John Wiley & Sons, Ltd. [source] Sleep Disturbances Reported by Refractory Partial-onset Epilepsy Patients Receiving PolytherapyEPILEPSIA, Issue 7 2006Xiao Xu Summary:,Purpose: Although sleep disturbances are common in epilepsy, few studies examined the prevalence and impact of sleep disturbance in epilepsy patients. This study investigates these in a cross-sectional survey. Methods: We surveyed 201 adult partial-onset epilepsy patients taking stable regimens of two or more antiepileptic medications. Community-based U.S. neurologists recorded patient demographic and clinical information. Patients completed the Medical Outcomes Study (MOS) Sleep Scale, the Quality of Life in Epilepsy-10 instrument (QOLIE-10), and the EuroQol-5D (EQ-5D). We evaluated the associations of sleep with health-related quality of life and clinical and demographic characteristics by using correlation coefficients and analysis of variance. Results: Mean (SD) age was 44.2 (12.5); 34% of patients had diagnosed sleep disturbances; 10% received prescription sleep medications. Patients with sleep disturbance reported poorer mean QOLIE-10 (55.2 vs. 63.7; p = 0.006) and EQ-5D (0.49 vs. 0.71; p < 0.001) scores relative to those without sleep disturbances. The mean (SD) MOS Sleep Problems Index score was 36.2 (20.8), worse than the general population mean of 26. Patients with physician-reported anxiety or depression had more sleep problems than did those without these comorbidities. Higher Sleep Problems Index scores were significantly (p < 0.001) correlated with poorer QOLIE-10 (r=,0.49) and EQ-5D (r=,0.56) scores. Patients experiencing a seizure within the past week reported higher MOS Sleep Problems Index scores than did those with a less-recent seizure (41.5 vs. 32.8; p = 0.003). Conclusions: Diagnosed and self-reported sleep disturbances in patients with partial-onset epilepsy are frequently overlooked, but are negatively associated with everyday functioning and well-being, and therefore contribute significantly to the burden of epilepsy. [source] A Bayesian model averaging approach for cost-effectiveness analysesHEALTH ECONOMICS, Issue 7 2009Caterina Conigliani Abstract We consider the problem of assessing new and existing technologies for their cost-effectiveness in the case where data on both costs and effects are available from a clinical trial, and we address it by means of the cost-effectiveness acceptability curve. The main difficulty in these analyses is that cost data usually exhibit highly skew and heavy-tailed distributions so that it can be extremely difficult to produce realistic probabilistic models for the underlying population distribution, and in particular to model accurately the tail of the distribution, which is highly influential in estimating the population mean. Here, in order to integrate the uncertainty about the model into the analysis of cost data and into cost-effectiveness analyses, we consider an approach based on Bayesian model averaging: instead of choosing a single parametric model, we specify a set of plausible models for costs and estimate the mean cost with a weighted mean of its posterior expectations under each model, with weights given by the posterior model probabilities. The results are compared with those obtained with a semi-parametric approach that does not require any assumption about the distribution of costs. Copyright © 2008 John Wiley & Sons, Ltd. [source] The health status burden of people with fibromyalgia: a review of studies that assessed health status with the SF-36 or the SF-12INTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 1 2008D. L. Hoffman Summary Objective:, The current review describes how the health status profile of people with fibromyalgia (FM) compares to that of people in the general population and patients with other health conditions. Methods:, A review of 37 studies of FM that measured health status with the 36-item Medical Outcomes Study Short-Form Health Survey (SF-36) or the 12-item Short-Form Health Survey (SF-12). Results:, Studies performed worldwide showed that FM groups were significantly more impaired than people in the general population on all eight health status domains assessed. These domains include physical functioning, role functioning difficulties caused by physical problems, bodily pain, general health, vitality (energy vs. fatigue), social functioning, role functioning difficulties caused by emotional problems and mental health. FM groups had mental health summary scores that fell 1 standard deviation (SD) below the general population mean, and physical health summary scores that fell 2 SD below the general population mean. FM groups also had a poorer overall health status compared to those with other specific pain conditions. FM groups had similar or significantly lower (poorer) physical and mental health status scores compared to those with rheumatoid arthritis, osteoarthritis, osteoporosis, systemic lupus erythematosus, myofacial pain syndrome, primary Sjögren's syndrome and others. FM groups scored significantly lower than the pain condition groups mentioned above on domains of bodily pain and vitality. Health status impairments in pain and vitality are consistent with core features of FM. Conclusions:, People with FM had an overall health status burden that was greater in magnitude compared to people with other specific pain conditions that are widely accepted as impairing. [source] On the Construction of Imputation Classes in SurveysINTERNATIONAL STATISTICAL REVIEW, Issue 1 2007David Haziza Summary This paper explores the problem of the construction of imputation classes using the score method, sometimes called predictive mean stratification or response propensity stratification, depending on the context. This method was studied in Thomsen (1973), Little (1986) and Eltinge & Yansaneh (1997). We use a different framework to evaluate the properties of the resulting imputed estimator of a population mean. In our framework, we condition on the realized sample. This enables us to considerably simplify our theoretical developments in the frequent situation where the boundaries and the number of classes are sample-dependent. We find that the key factor for reducing the non-response bias is to form classes homogeneous with respect to the response probabilities and/or the conditional expectation of the variable of interest. In the latter case, the non-response/imputation variance is also reduced. Finally, we performed a simulation study to fully evaluate various versions of the score method and to compare them with a cross-classification method, which is frequently used in practice. The results showed the superiority of the score method in general. Résumé Cet article étudie la construction des classes d'imputation par la méthode des scores, appelée également stratification par moyenne prédite ou stratification par propensité de réponse selon le contexte. Cette méthode a étéétudiée par Thomsen (1973), Little (1986) et Eltinge et Yansaneh (1997). Nous utilisons un cadre de travail différent permettant d'évaluer les propriétés de l'estimateur imputé de la moyenne de la population selon lequel nous conditionnons sur l'échantillon réalisé. Ceci nous permet de simplifier considérablement les développements théoriques lorsque les bornes et le nombre de classes dépendent de l'échantillon, ce qui survient fréquemment en pratique. Nous déterminons que le facteur clé permettant de réduire le biais du à la non-réponse est de former des classes qui soient homogènes par rapport aux probabilités de réponse et/ou à l'espérance conditionnelle de la variable d'intérêt. Dans ce dernier cas, la variance due à la non-réponse et à l'imputation est également réduite. Finalement, nous effectuons une étude par simulation afin d'évaluer en profondeur plusieurs versions de la méthode des scores et de comparer celles-ci avec la méthode par croisement qui est fréquemment utilisée en pratique. Les résultats obtenus montrent la supériorité de la méthode des scores en général. [source] Effect of various estimates of renal function on prediction of vancomycin concentration by the population mean and Bayesian methodsJOURNAL OF CLINICAL PHARMACY & THERAPEUTICS, Issue 4 2009Y. Tsuji BSc Summary Objective:, Renal function was estimated in 129 elderly patients with methicillin-resistant Staphylococcus aureus (MRSA) who were treated with vancomycin (VCM). The estimation was performed by substituting serum creatinine (SCR) measured enzymatically and a value converted using the Jaffe method into the Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) equations. The serum trough level was predicted from three estimates of renal function by the population mean (PM) and Bayesian methods and the predictability was assessed. Methods:, Two-compartment model-based Japanese population parameters for VCM were used, and the mean prediction error (ME) and root mean squared error (RMSE) were calculated as indices of bias and accuracy, respectively, for predictions by the PM and Bayesian methods. Results:, The PM method gave the highest correlation with the measured value using the estimate of renal function obtained by substituting the Jaffe-converted SCR into the Cockcroft-Gault equation. There was no positive or negative bias in the ME and the value was significantly smaller than for other predicted data (P < 0·05). RMSE was also the smallest, indicating that this method increases the predictability of the serum VCM trough level. While, ME showed a negative bias for all values predicted by the Bayesian method, both the ME and RMSE were very small. Conclusion:, In the application of the PM method for VCM treatment of elderly patients with MRSA, substitution of SCR based on the Jaffe method into the Cockcroft-Gault equation increases the predictability of the serum VCM trough level. The Bayesian method predicted the serum VCM trough level with high accuracy using any of the estimates of renal function. [source] Cognitive abilities, behaviour and quality of life in children after liver transplantationPEDIATRIC TRANSPLANTATION, Issue 4 2010T. Kaller Kaller T, Boeck A, Sander K, Richterich A, Burdelski M, Ganschow R, Schulz KH. Cognitive abilities, behaviour and quality of life in children after liver transplantation. Pediatr Transplantation 2010: 14:496,503. © 2010 John Wiley & Sons A/S. Abstract:, Aims:, We investigated interrelations between cognitive abilities, behavioural problems, quality of life and disease-related variables of children after LTX. Methods:, Our sample consisted of 25 children. They were 8.5/2.8 (M/SD) years old and had received the transplant 5.5/3.1 years previously. For assessment we used well-established instruments. Results:, Liver transplanted children scored below the population mean on the cognitive as well as on the behavioural instrument and showed scores below average in the scales Self-esteem, Friends and Total Score regarding QoL. Behavioural problems were associated with poorer cognitive performance (r=,0.38 to ,0.63). QoL regarding physical well-being was correlated with sequential processing (r=0.41). Lower sequential processing scores were associated with lower QoL. Also between behavioural parameters and QoL correlations could be determined. Children with more behavioural problems experienced lower QoL (r=,0.40 to r=,0.76). Age at onset of disease showed correlations with behavioural and QoL parameters (r=,0.49 resp. r=0.44). Cognitive functioning was associated with medical complications (r=,0.44). Conclusions:, High interrelations between cognitive functioning, behavioural deficits and QoL were obtained. Especially noticeable are correlations between sequential processing and internalized behavioural functions as both are associated with left lateralized brain functioning. This relationship could indicate differential effects on brain development during the preoperative phase. [source] Morphometric variation in the papionin muzzle and the biochronology of the South African Plio-Pleistocene karst cave depositsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2010Christopher C. Gilbert Abstract Papionin monkeys are widespread, relatively common members of Plio-Pleistocene faunal assemblages across Africa. For these reasons, papionin taxa have been used as biochronological indicators by which to infer the ages of the South African karst cave deposits. A recent morphometric study of South African fossil papionin muzzle shape concluded that its variation attests to a substantial and greater time depth for these sites than is generally estimated. This inference is significant, because accurate dating of the South African cave sites is critical to our knowledge of hominin evolution and mammalian biogeographic history. We here report the results of a comparative analysis of extant papionin monkeys by which variability of the South African fossil papionins may be assessed. The muzzles of 106 specimens representing six extant papionin genera were digitized and interlandmark distances were calculated. Results demonstrate that the overall amount of morphological variation present within the fossil assemblage fits comfortably within the range exhibited by the extant sample. We also performed a statistical experiment to assess the limitations imposed by small sample sizes, such as typically encountered in the fossil record. Results suggest that 15 specimens are sufficient to accurately represent the population mean for a given phenotype, but small sample sizes are insufficient to permit the accurate estimation of the population standard deviation, variance, and range. The suggestion that the muzzle morphology of fossil papionins attests to a considerable and previously unrecognized temporal depth of the South African karst cave sites is unwarranted. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source] Rapid changes in clonal lines: the death of a ,sacred cow'BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2003HUGH D. LOXDALE It is well established that asexually reproducing viruses and prokaryotes mutate rapidly. In contrast, the eukaryotic clone is often still treated as if it is genetically homogeneous within and between populations, i.e. that it is assumed to show genetic fidelity. However, such fidelity has rarely been tested empirically using the range of high-resolution molecular markers now available, culminating with direct sequencing of the DNA. If such a biological entity as a ,clone' really did exist, it would be a fantastic entity, differing from everything else known in biology, i.e. it would possess a population mean but no variance for any particular trait. It would not be amenable to selection and adaptive variation and would thus be unchanging in time and space. In this paper, we argue that the general acceptance of clonal fidelity is a scientific convenience, since the rate of asexual reproduction of eukaryotes is not as fast as that of bacteria and hence it is easier to accept fidelity as a ,fact' rather than test for it. We propose that part of the acceptance of fidelity may have a cultural basis and thereby is a kind of ,pre-Darwinian relic'. Instead, a clonal genotype is perhaps largely a function of marker resolution, i.e. dependent on the number and type of markers employed. If this is so and were enough of the genome explored, perhaps each individual within a clone would be found to differ genetically at particular regions of the chromosomes. The question of what constitutes a clone is not just a semantic one and impacts directly on recent attempts to understand and produce ,artificial' clones, especially of mammals. New research is already confirming that mutations and epigenetic influences play a crucial role in the success of cloning attempts. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society, 2003, 79, 3,16. [source] Ranked Set Sampling: Cost and Optimal Set SizeBIOMETRICS, Issue 4 2002Ramzi W. Nahhas Summary. Mclntyre (1952, Australian Journal of Agricultural Research3, 385,390) introduced ranked set sampling (RSS) as a method for improving estimation of a population mean in settings where sampling and ranking of units from the population are inexpensive when compared with actual measurement of the units. Two of the major factors in the usefulness of RSS are the set size and the relative costs of the various operations of sampling, ranking, and measurement. In this article, we consider ranking error models and cost models that enable us to assess the effect of different cost structures on the optimal set size for RSS. For reasonable cost structures, we find that the optimal RSS set sizes are generally larger than had been anticipated previously. These results will provide a useful tool for determining whether RSS is likely to lead to an improvement over simple random sampling in a given setting and, if so, what RSS set size is best to use in this case. [source] EXPERIMENTAL EVIDENCE FOR MULTIVARIATE STABILIZING SEXUAL SELECTIONEVOLUTION, Issue 4 2005Robert Brooks Abstract Stabilizing selection is a fundamental concept in evolutionary biology. In the presence of a single intermediate optimum phenotype (fitness peak) on the fitness surface, stabilizing selection should cause the population to evolve toward such a peak. This prediction has seldom been tested, particularly for suites of correlated traits. The lack of tests for an evolutionary match between population means and adaptive peaks may be due, at least in part, to problems associated with empirically detecting multivariate stabilizing selection and with testing whether population means are at the peak of multivariate fitness surfaces. Here we show how canonical analysis of the fitness surface, combined with the estimation of confidence regions for stationary points on quadratic response surfaces, may be used to define multivariate stabilizing selection on a suite of traits and to establish whether natural populations reside on the multivariate peak. We manufactured artificial advertisement calls of the male cricket Teleogryllus commodus and played them back to females in laboratory phonotaxis trials to estimate the linear and nonlinear sexual selection that female phonotactic choice imposes on male call structure. Significant nonlinear selection on the major axes of the fitness surface was convex in nature and displayed an intermediate optimum, indicating multivariate stabilizing selection. The mean phenotypes of four independent samples of males, from the same population as the females used in phonotaxis trials, were within the 95% confidence region for the fitness peak. These experiments indicate that stabilizing sexual selection may play an important role in the evolution of male call properties in natural populations of T. commodus. [source] | ||||||||||||||||