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PubMed1991

Further issues in small area variations analysis.

In this article, I examine Wennberg's "practice style" hypothesis and the literature on variations among small areas. According to Wennberg, geographic variations in rates of per capita use for many clinical procedures arise mainly from differences over what constitutes appropriate care. I show, however, that the role of practice style in explaining variations among areas has not been clearly demonstrated. I also argue that the practice style hypothesis can neither be established nor refuted by the methods traditionally used to study small areas and, moreover, that inferences about practice style variations cannot be drawn from differences among areas in their rates of use. I thus conclude that more research at the micro level in the practice patterns of the individual physician is needed before major health care initiatives based on small area methodology are undertaken.

Health Policy↗

PubMed2004

Phylogenetic analysis of the nuclear alcohol dehydrogenase (Adh) gene family in Carex section Acrocystis (Cyperaceae) and combined analyses of Adh and nuclear ribosomal ITS and ETS sequences for inferring species relationships.

We analyzed sequence variation for the alcohol dehydrogenase (Adh) gene family in Carex section Acrocystis (Cyperaceae) to reconstruct Adh gene trees for Acrocystis species and to characterize the structure of the Adh gene family in Carex. Two Adh loci were included with ITS and ETS sequences in a combined Bayesian inference analysis of Carex section Acrocystis to gain a better understanding of species relationships in the section. In addition, we comment on how the results presented here contribute to our knowledge of the birth-death process of the Adh gene family in angiosperms. It appears that the structure of the Adh gene family in Carex is complex with possibly six loci present in the gene family. Additionally, variation among Acrocystis species within loci is quite low, and there is little phylogenetic resolution in the individual datasets. Bayesian inference analysis of the combined ITS, ETS, Adh1, and Adh2 datasets resulted in a moderately well-supported phylogenetic hypothesis of relationships in the section which is discussed in relation to previous hypotheses of relationships.

Alcohol Dehydrogenase↗

PubMed1997

Quantitative trait loci differentiating the outbreeding Mimulus guttatus from the inbreeding M. platycalyx.

Theoretical predictions about the evolution of selfing depend on the genetic architecture of loci controlling selfing (monogenic vs. polygenic determination, large vs. small effect of alleles, dominance vs. recessiveness), and studies of such architecture are lacking. We inferred the genetic basis of mating system differences between the outbreeding Mimulus guttatus and the inbreeding M. platycalyx by quantitative trait locus (QTL) mapping using random amplified polymorphic DNA and isozyme markers. One to three QTL were detected for each of five mating system characters, and each QTL explained 7.6-28.6% of the phenotypic variance. Taken together, QTL accounted for up to 38% of the variation in mating system characters, and a large proportion of variation was unaccounted for. Inferred QTL often affected more than one trait, contributing to the genetic correlation between those traits. These results are consistent with the hypothesis that quantitative variation in plant mating system characters is primarily controlled by loci with small effect.

Chromosome Mapping↗

PubMed2004

Differences, disparities, and biases: clarifying racial variations in health care use.

Studies documenting racial differences in health care use are common in the medical literature. However, observational studies of racial differences in health care use lack a framework for interpreting reports of variations in health care use, leading to various terms, ranging from "variations" to "bias," that suggest different causes, consequences, and, ultimately, remedies for such variations in treatment. We propose criteria to assess racial differences in health care use by using a clinical equity (equal treatment based on equal clinical need) framework. This framework differentiates between initial reports of racial differences and subsequent classifications of their findings as racial disparities or racial bias in health care use. Racial variations in health care use may be considered disparities after demonstrating that racial differences are not attributable to treatment eligibility, clinical contraindications, patient preferences, or confounding by other clinical factors and are associated with adverse consequences. Racial bias with adverse consequences in health care may be inferred if a racial variation in treatment that has been characterized as a disparity persists after accounting for health care system factors (for example, type of hospital at which the patient was treated). We apply this framework to published reports of racial differences in treatment to determine which studies provide evidence of differences, disparities, and bias. We discuss the use of such a framework in directing policy interventions for alleviating inappropriate racial variations in health care use.

Delivery of Health Care↗

PubMed2003

Features of evolution and expansion of modern humans, inferred from genomewide microsatellite markers.

We study data on variation in 52 worldwide populations at 377 autosomal short tandem repeat loci, to infer a demographic history of human populations. Variation at di-, tri-, and tetranucleotide repeat loci is distributed differently, although each class of markers exhibits a decrease of within-population genetic variation in the following order: sub-Saharan Africa, Eurasia, East Asia, Oceania, and America. There is a similar decrease in the frequency of private alleles. With multidimensional scaling, populations belonging to the same major geographic region cluster together, and some regions permit a finer resolution of populations. When a stepwise mutation model is used, a population tree based on TD estimates of divergence time suggests that the branches leading to the present sub-Saharan African populations of hunter-gatherers were the first to diverge from a common ancestral population (approximately 71-142 thousand years ago). The branches corresponding to sub-Saharan African farming populations and those that left Africa diverge next, with subsequent splits of branches for Eurasia, Oceania, East Asia, and America. African hunter-gatherer populations and populations of Oceania and America exhibit no statistically significant signature of growth. The features of population subdivision and growth are discussed in the context of the ancient expansion of modern humans.

Africa↗

PubMed2001

A model for phylogenetic inference using structural and chemical covariates.

We investigated whether or not evolutionary change in DNA sequence data was homogeneous across different classes of base pairs. DNA sequences for eight protein-coding mitochrondrial genes were obtained for 38 vertebrate taxa from GenBank. Each nucleotide site in the alignment was classified according to a number of covariates, including its codon position, genetic code degeneracy, and hydrophobicity. The evolutionary transition matrix for each base was estimated by tracing implied character changes under parsimony on a known phylogenetic tree. Canonical variates analyses of the inferred transition matrices were performed for each gene to determine whether or not different classes of bases behaved similarly. We found five distinct clusters of transition matrices that could be roughly defined by combinations of codon position and degeneracy. This pattern was consistent among all genes. A stochastic model of rate variation based on the interaction of the covariates was developed to assess the statistical significance of the clusters. The five-group classification was found to explain significantly more sequence variation than did a codon only classification, a codon degeneracy classification, or a codon and degeneracy classification. The same five-group classification was found for all genes tested, suggesting a common process underlying the molecular evolution of the mitochondrial genome. These results confirm that there are classes of base pairs that evolve differently, and suggest that models of sequence evolution that incorporate covariate information may be useful in developing nucleotide substitution models that more accurately reflect evolutionary history.

Animals↗

PubMed1998

Levels of genetic polymorphism: marker loci versus quantitative traits.

Species are the units used to measure ecological diversity and alleles are the units of genetic diversity. Genetic variation within and among species has been documented most extensively using allozyme electrophoresis. This reveals wide differences in genetic variability within, and genetic distances among, species, demonstrating that species are not equivalent units of diversity. The extent to which the pattern observed for allozymes can be used to infer patterns of genetic variation in quantitative traits depends on the forces generating and maintaining variability. Allozyme variation is probably not strictly neutral but, nevertheless, heterozygosity is expected to be influenced by population size and genetic distance will be affected by time since divergence. The same is true for quantitative traits influenced by many genes and under weak stabilizing selection. However, the limited data available suggest that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations. It is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species, but is only weakly correlated with prezygotic isolation. Studies of grasshopper and planthopper mating signal variation and assortative mating illustrate how these characters evolve independently of general genetic and morphological variation. The role of such traits in prezygotic isolation, and hence speciation, means that they will contribute significantly to the diversity of levels of genetic variation within and among species.

Alleles↗

PubMed2001

Reproducibility of optical biometry using partial coherence interferometry : intraobserver and interobserver reliability.

PURPOSE: To evaluate the intraobserver and interobserver variability in axial length (AL), anterior chamber depth (ACD), and corneal radius measurements using an optical biometry instrument based on partial coherence interferometry (PCI). SETTING: Johannes Gutenberg University, Mainz, Germany. METHODS: In this observational case series and interobserver reliability trial, 30 healthy, emmetropic to moderately myopic eyes of 15 volunteers were evaluated. The AL, ACD, and corneal radius were measured 20 times in 10 eyes by 1 observer to evaluate the intraobserver variability. To evaluate the interobserver variability, the measurements were taken in 20 eyes by 5 different observers. Measurements were performed using the IOLMaster (Carl Zeiss) based on PCI. The data description is based on coefficients of variation and the statistical inference on reliability estimation based on analysis of variance. The main outcome measures were intraobserver and interobserver variability and reliability in AL, ACD, and corneal radii. RESULTS: The intraobserver variability (SD) was +/-25.6 microm for AL, +/-33.4 microm for ACD, and +/-12.9 microm for corneal radius. The coefficients of variation were 0.1%, 0.9%, and 0.17%, respectively. The interobserver variability (SD) was +/-21.5 microm for AL, +/-29.8 microm for ACD, and +/-15.9 microm for corneal radius. The coefficients of variation were 0.09%, 0.82%, and 0.21%, respectively. The reliability was 99.9% for AL, 97.8% for ACD, and 99.8%/99.5% for corneal radius (r1/r2). The slightly reduced reliability in ACD measurement was caused by a reduced intraobserver reliability of 1 of the 5 observers (R = 0.87). CONCLUSION: Partial coherence biometry using the IOLMaster for AL measurement was highly reliable, offering observer-independent measurement results.

Adult↗

PubMedDate not supplied

[Tobacco smoke and malignant tumors. Analysis by birth cohorts from 1875 to 1935].

Over the last decades, the relationship between tobacco smoking and cancer has been studied utilizing all the models available to research. The epidemiological researches, that are carried out on human populations, constitute the study model which can provide definitive evidence on the considered association. Among the several cancer sites, cancer of the lung, oral cavity and pharynx, esophagus, larynx, pancreas and urinary bladder are the sites more directly related with smoking habits. In this research the relationship between these cancer sites and tobacco smoking was studied examining both the international literature, and applying the cohort analysis to Italian mortality data from 1950 to 1983. The birth cohorts considered were those from 1875 to 1935 and data on cancer deaths are derived from official ISTAT publications. The analysis of cohort variation was carried out utilizing the indirect standardization method. The data on tobacco consumption, from 1900 to 1985, was obtained from official publication of the Administration of the State Monopolies or from unpublished material kindly provided by the same Administration. Regarding lung cancer, literature data emphasize the relationship between the disease frequency and age of starting smoking and the type of tobacco smoked. In Italy cohort variation seems to indicate an increased risk in mortality for men born before 1925, but there are indications of levelling off after this year. Analysis of the consumption of different types of tobacco products since 1900 suggests that the trends of mortality with time in different birth cohorts are explicable in terms of changes in the use of cigarettes, with high tar content up to 1940-1950, with low tar content and filter tipped after the 50s. Regarding females from the cohort variation it can be inferred that in Italy women began to smoke more recently and tobacco consumption is referred, almost exclusively, to low-tar and filter-tipped cigarettes. For larynx cancer, the literature data report that the relative risk is related to smoking habits and the present analysis shows a cohort variation very similar to that for lung cancer. Smoking habits, alcohol consumption, and their interaction, constitute the principal risk factor both for esophagus cancer and that of oral cavity and pharynx. In Italy the risk derived from alcohol consumption has influenced the trends of cohort variation relative to these two sites, which contrary to lung and larynx cohort trends, shows some fluctuations in mortality in males before 1921 and a progressive increase after this year. The relationship relative to urinary bladder and pancreas cancer is less evident.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2006

Seasonal variation of transient acantholytic dyskeratosis (Grover's disease).

BACKGROUND: Grover's disease (GD), or transient acantholytic dermatosis, is a pruritic, papulovesicular eruption characterized histopathologically by acantholysis with or without dyskeratosis. The origin of GD is unknown. Suggested causes include sweating, heat, immobilization occlusion, external beam and ultraviolet radiation, and xerosis. GD has also been found to occur in association with other diseases. OBJECTIVE: Our aim was to assess whether GD exhibits seasonal variation and, if so, to determine whether any inferences can be drawn from its seasonal variation regarding its cause. METHODS: We identified 385 patients who fulfilled both clinical and histopathologic criteria for GD among 423,106 patients diagnosed at the Ackerman Academy of Dermatopathology in New York City during the period from July 1, 1999 through June 30, 2004. By design, no hospitalized patients were studied. RESULTS: A diagnosis of GD was given to 0.09% of biopsy specimens at the Ackerman Academy of Dermatopathology. GD was diagnosed approximately 4 times more commonly in winter than in summer, although the number of biopsies was constant. The average age of GD patients was 64 years with a male/female ratio of 1.95:1. The most common histopathologic type of GD was pemphigus vulgaris. GD was suspected clinically in 54% of patients. LIMITATIONS: This study did not assess hospitalized patients with GD or GD patients who lived outside the northeastern United States. Because the data assessed resided in a commercial dermatopathology laboratory, patients assessed in almost all cases had insurance coverage. Patients without insurance likely were not included in the study. CONCLUSIONS: The diagnosis of GD constitutes a higher proportion of biopsies in the winter than in the summer and therefore, by inference, occurs more frequently in the winter. In the winter, elderly men whose skin is naturally xerotic sweat less and are exposed to low ambient humidity. Rather than being caused by sweating and heat, GD arises against a backdrop of an intact but xerotic epidermis with decreased sweat production and is likely related to impaired epidermal integrity.

Acantholysis↗

PubMed2001

DNA variation at the rp49 gene region of Drosophila simulans: evolutionary inferences from an unusual haplotype structure.

An approximately 1.3-kb region including the rp49 gene plus its 5' and 3' flanking regions was sequenced in 24 lines of Drosophila simulans (10 from Spain and 14 from Mozambique). Fifty-four nucleotide and 8 length polymorphisms were detected. All nucleotide polymorphisms were silent: 52 in noncoding regions and 2 at synonymous sites in the coding region. Estimated silent nucleotide diversity was similar in both populations (pi = 0.016, for the total sample). Nucleotide variation revealed an unusual haplotype structure showing a subset of 11 sequences with a single polymorphism. This haplotype was present at intermediate frequencies in both the European and the African samples. The presence of such a major haplotype in a highly recombining region is incompatible with the neutral equilibrium model. This haplotype structure in both a derived and a putatively ancestral population can be most parsimoniously explained by positive selection. As the rate of recombination in the rp49 region is high, the target of selection should be close to or within the region studied.

Animals↗

PubMed1999

A comparison of the nariokotome Homo erectus with juveniles from a modern human population.

The Nariokotome Homo erectus has an apparent disjunction of inferred age as judged by dental maturity, by epiphyseal closure and by stature, when compared to modern human norms. On this basis, it has been suggested that this fossil hominin differed in its pattern of growth and development from modern humans. In particular, the characteristic human adolescent growth spurt may not yet have been present, and in this sense H. erectus growth would be more ape-like than human-like. This study tests this conclusion by examining the variation in age as inferred from the maturity indicators in a modern human skeletal population of known age. The results show that all of the maturity indicators used in this analysis underage the test skeletons. Furthermore, there is also no consistency between the indicators; they do not agree in their inferred chronological ages. The disjunction between the maturity indicators in the test skeletons is similar in pattern to the disjunction observed in the Nariokotome Homo erectus. This is particularly true of the relationship between dental age and the other two indicators. These results suggest that the pattern observed in Nariokotome is within the normal range of variation found in modern humans. It does not necessarily indicate a different pattern of growth and development.

Adolescent↗

PubMed2003

DNA variation in a 13-Mb region including the F9 gene: inferring the genealogical history and causal role of a hemophilia B mutation (IVS 5+13 A-->G).

About 5.5% of all UK hemophilia B patients have the base substitution IVS 5+13 A-->G as the only change in their factor (F)IX gene (F9). This generates a novel donor splice site which fits the consensus better than the normal intron 5 donor splice. Use of the novel splice site should result in a missense mutation followed by the abnormal addition of four amino acids to the patients' FIX. In order to explain the prevalence of this mutation, its genealogical history is examined. Analysis of restriction fragment length polymorphism in the 21 reference UK individuals (from different families) with the above mutation showed identical haplotypes in 19 while two differed from the rest and from each other. In order to investigate the history of the mutation and to verify that it had occurred independently more than once, the sequence variation in 1.5-kb segments scattered over a 13-Mb region including F9 was examined in 18 patients and 15 controls. This variation was then analyzed with a recently developed Bayesian approach that reconstructs the genealogy of the gene investigated while providing evidence of independent mutations that contribute disconnected branches to the genealogical tree. The method also provides minimum estimates of the age of the mutation inherited by the members of coherent trees. This revealed that 17 or 18 mutant genes descend from a founder who probably lived 450 years ago, while one patient carries an independent mutation. The independent recurrence of the IVS5+13 A-->G mutation strongly supports the conclusion that it is the cause of these patients' mild hemophilia.

Base Sequence↗

PubMed2000

A phylogeny of Apiaceae tribe Scandiceae: evidence from nuclear ribosomal DNA internal transcribed spacer sequences.

The evolutionary relationships among members of Apiaceae (Umbelliferae) tribe Scandiceae and representatives of all major lineages of Apioideae (including putatively allied Caucalideae) identified in earlier molecular studies were inferred from nucleotide sequence variation in the internal transcribed spacer regions (ITS1 and ITS2) of nuclear ribosomal DNA. In all, 134 accessions representing 18 genera commonly treated in Scandiceae were analyzed. Phylogenies estimated using maximum parsimony and distance methods were generally similar and suggest that: (1) Scandiceae form a well-supported clade, consisting of the genera Anthriscus, Athamanta (in part), Balansaea, Chaerophyllum, Conopodium, Geocaryum, Kozlovia, Krasnovia, Myrrhis, Myrrhoides, Neoconopodium, Osmorhiza, Scandix, Sphallerocarpus, and Tinguarra; (2) Athamanta is polyphyletic, with A. della-cellae allied with Daucus and A. macedonica placed close to Pimpinella; and (3) Rhabdosciadium and Grammosciadium find affinity with the Aegopodium group of umbellifers, whereas the placement of the monotypic Molopospermum cannot be inferred because of its high sequence divergence. The genus Bubon has been restored with two new combinations, B. macedonicum subsp. albanicum and B. macedonicum subsp. arachnoideum. Scandiceae arise within paraphyletic Caucalideae, the latter comprising two major lineages whose relationships to Scandiceae are not clear. Therefore, a broad treatment of Scandiceae is proposed, with subtribes Scandicinae, Daucinae, and Torilidinae (the latter two representing the Daucus and Torilis subgroups, respectively, of recent molecular systematic investigations).

Journal Article↗

PubMed1992

Sexual dimorphism in the human bony pelvis, with a consideration of the Neandertal pelvis from Kebara Cave, Israel.

Sexual dimorphism of the human pelvis is inferentially related to obstetrics. However, researchers disagree in the identification and obstetric significance of pelvic dimorphisms. This study addresses three issues. First, common patterns in dimorphism are identified by analysis of pelvimetrics from six independent samples (Whites and Blacks of known sex and four Amerindian samples of unknown sex). Second, an hypothesis is tested that the index of pelvic dimorphism (female mean x 100/male mean) is inversely related to pelvic variability. Third, the pelvic dimensions of the Neandertal male from Kebara cave, Israel are compared with those of the males in this study. The results show that the pelvic inlet is the plane of least dimorphism in humans. The reason that reports often differ in the identification of dimorphisms for this pelvic plane is that both the length of the pubis and the shape of the inlet are related to nutrition. The dimensions of the pelvis that are most dimorphic (that is, female larger than male) are the measures of posterior space, angulation of sacrum, biischial breadth, and subpubic angle. Interestingly, these dimensions are also the most variable. The hypothesis that variability and dimorphism are inversely related fails to be supported. The factors that influence pelvic variability are discussed. The Kebara 2 pelvis has a spacious inlet and a confined outlet relative to modern males, though the circumferences of both planes in the Neandertal are within the range of variation of modern males. The inference is that outlet circumference in Neandertal females is also small in size, but within the range of variation of modern females. Arguments that Neandertal newborns were larger in size than those of modern humans necessarily imply that birth was more difficult in Neandertals.

Animals↗

PubMed2002

Reproductive mode and genetic variation suggest a North American origin of European Letharia vulpina.

Our data on the intercontinental population biology of Letharia vulpina show an unexpected shift from a recombining North American population with unique haplotypes to genetically depauperate Swedish and Italian populations, each with many representatives of a single repeated haplotype. Analysis of eight loci in 47 individuals supported recombination in North American populations and showed almost no variation among European populations. We infer that a genetic bottleneck caused by limited long-distance dispersal accounts for the lack of genetic variation found in marginal populations. This lack of variation in the European populations makes it impossible to use population genetic means to distinguish clonal reproduction from self-fertilization or even outcrossing, but phenotype indicates that reproduction in the marginal populations is by clonal spread, via soredia and isidioid soredia.

Ascomycota↗

PubMed2003

Evidence for survival of Pleistocene climatic changes in Northern refugia by the land snail Trochoidea geyeri (Soós 1926) (Helicellinae, Stylommatophora).

BACKGROUND: The study of organisms with restricted dispersal abilities and presence in the fossil record is particularly adequate to understand the impact of climate changes on the distribution and genetic structure of species. Trochoidea geyeri (Soós 1926) is a land snail restricted to a patchy, insular distribution in Germany and France. Fossil evidence suggests that current populations of T. geyeri are relicts of a much more widespread distribution during more favourable climatic periods in the Pleistocene. RESULTS: Phylogeographic analysis of the mitochondrial 16S rDNA and nuclear ITS-1 sequence variation was used to infer the history of the remnant populations of T. geyeri. Nested clade analysis for both loci suggested that the origin of the species is in the Provence from where it expanded its range first to Southwest France and subsequently from there to Germany. Estimated divergence times predating the last glacial maximum between 25-17 ka implied that the colonization of the northern part of the current species range occurred during the Pleistocene. CONCLUSION: We conclude that T. geyeri could quite successfully persist in cryptic refugia during major climatic changes in the past, despite of a restricted capacity of individuals to actively avoid unfavourable conditions.

Animals↗

PubMed2003

Extensive mtDNA variation within the yellow-pine chipmunk, Tamias amoenus (Rodentia: Sciuridae), and phylogeographic inferences for northwest North America.

The yellow-pine chipmunk, Tamias amoenus, is common in xerophytic forests throughout much of northwest North America. We analyzed cytochrome b sequence variation from 155 individuals representing 57 localities across the distribution of T. amoenus including 10 additional species of Tamias. Maximum likelihood and parsimony tree estimation methods were used in conjunction with nested clade analysis to infer both deep and population-level processes. Our results indicate that two currently recognized subspecies of T. amoenus (T. a. canicaudus and T. a. cratericus) are not nested within other samples of T. amoenus. Maximum uncorrected levels of intraspecific sequence divergence within remaining samples of T. amoenus are >7%. Substantial geographic variation is characterized by 12 well-supported clades that correspond to distinct mountain ranges, but do not necessarily follow existing subspecific taxonomy. Significant association between geography and genealogy was detected within many of these clades and can be attributed to different population-level processes including past fragmentation, recent range expansion, and isolation by distance.

Animals↗