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Theoretical Concerns (theoretical + concern)

Distribution by Scientific Domains

Life Sciences	40%

Selected Abstracts

Estimation of rate ratio and relative difference in matched-pairs under inverse sampling

ENVIRONMETRICS, Issue 6 2001
Kung-Jong Lui
Abstract To increase the efficiency of a study and to eliminate the effects of some nuisance confounders, we may consider employing a matched-pair design. Under the commonly assumed quadrinomial sampling, in which the total number of matched-pairs is fixed, we note that the maximum likelihood estimator (MLE) of rate ratio (RR) has an infinitely large bias and no finite variance, and so does the MLE of relative difference (RD). To avoid this theoretical concern, this paper suggests use of an inverse sampling and notes that the MLEs of these parameters, which are actually of the same forms as those under the quadrinomial sampling, are also the uniformly minimum variance estimators (UMVUEs) under the proposed samplings. This paper further derives the exact variances of these MLEs and the corresponding UMVUEs of these variances. Finally, this paper includes a discussion on interval estimation of the RR and RD using these results as well. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Lancaster's characteristics approach revisited: product selection using non-parametric methods

MANAGERIAL AND DECISION ECONOMICS, Issue 2 2002
Angel S. Fernandez-Castro
In consumer theory, the principles of Lancaster's characteristics approach and hedonic pricing appear to offer the most promising insight into choice when qualitative aspects are important. The paper reconciles these principles with the family of non-parametric frontier estimation methods known as data envelopment analysis. It is shown that, with some straightforward adjustments, DEA is entirely consistent with the characteristics view of consumer choice found in the economics literature. In making Lancaster's ideas operational, the paper also addresses the theoretical concern voiced by Lancaster about combining indivisible products. The principles are illustrated with a case study involving the comparison of diesel cars. The paper concludes that the user will ultimately have to apply some judgement in choosing between competing efficient products. However, the analysis should help to restrict the number of products to be assessed to manageable proportions. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Pollination ecology of Isoglossa woodii, a long-lived, synchronously monocarpic herb from coastal forests in South Africa

PLANT BIOLOGY, Issue 3 2010
M. E. Griffiths
Abstract Synchronous monocarpy in long-lived plants is often associated with pollination by wind, in part because infrequent mass flowering may satiate pollinators. Selfing in synchronous monocarps may provide reproductive assurance but conflict with the benefits of outcrossing, a key evolutionary driver of synchrony. We predicted that animal-pollinated species with synchronous flowering would have unspecialised flowers and attract abundant generalised pollinators, but predictions for selfing and outcrossing frequencies were not obvious. We examined the pollination biology of Isoglossa woodii (Acanthaceae), an insect-pollinated, monocarpic herb that flowers synchronously at 4,7-year intervals. The most frequent visitor to I. woodii flowers was the African honeybee, Apis mellifera adansonii. Hand-pollination failed to enhance seed production, indicating that the pollinators were not saturated. No seed was set in the absence of pollinators. Seed set was similar among selfed and outcrossed flowers, demonstrating a geitonogamous mixed-mating strategy with no direct evidence of preferential outcrossing. Flowers contained four ovules, but most fruits only developed one seed, raising the possibility that preferential outcrossing occurs by post-pollination processes. We argue that a number of the theoretical concerns about geitonogamous selfing as a form of reproductive assurance do not apply to a long-lived synchronous monocarp such as I. woodii. [source]

Stature estimation in an early medieval (XI-XII c.) Polish population: Testing the accuracy of regression equations in a bioarcheological sample

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009
Giuseppe Vercellotti
Abstract Accurate stature estimation from skeletal remains can foster useful information on health and microevolutionary trends in past human populations. Stature can be estimated through the anatomical method and regression equations. The anatomical method (Fully: Ann Med Leg 36 [1956] 266,273; Raxter et al.: Am J Phys Anthropol 130 [2006] 374,384) is preferable because it takes into account total skeletal height and thus provides more accurate estimates, but it cannot be applied to incomplete remains. In such circumstances, regression equations allow estimates of living stature from the length of one or few skeletal elements. However, the accuracy of stature estimates from regression equations depends on similarity in body proportions between the population under examination and those used to calibrate the equations. Since genetic affinity and body proportions similarity are not always clearly known in bioarcheological populations, the criteria for selection of appropriate formulae are not always straightforward. This may lead to inaccurate stature estimates and imprecise accounts of past life conditions. Prompted by such practical and theoretical concerns this study aimed at (1) estimating living stature in an early medieval (XI-XII c.) Polish sample (40 male; 20 female) through the anatomical method and developing population-specific regression formulae; and (2) evaluating the accuracy of estimates obtained with regression methods commonly employed in European populations. Results indicate that when applied to the skeletal remains from Giecz, our formulae provide accurate estimates, with non-age-corrected formulae performing better than age-corrected ones. Our formulae provide better estimates than those calibrated on recent populations and their use in medieval Polish populations is preferable. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source]

Intensive interaction and autism: some theoretical concerns

CHILDREN & SOCIETY, Issue 2 2000
Melanie Nind
The authors consider the possible application of intensive interaction to children with autism. Intensive interaction is briefly described, and the question asked whether children with autism (and developmental delay) can gain from this exemplar of naturalistic, interactive approaches to facilitating sociability and communication. A theoretical approach is taken to unravel the difficulties faced by children with autism in developing sociability and communication, and the way in which intensive interaction functions. Five areas of possible mismatch between the particular difficulties/needs of these children and the method are identified and interrogated. The authors conclude that children with autism can be enabled to learn about interaction and communication through this naturalistic and supportive process. The need for empirical evidence to substantiate this position is highlighted. Copyright © 2000 John Wiley & Sons, Ltd. [source]