Home About us Contact
|
Home About us Contact | ||
|
|
||
Successive Cohorts (successive + cohort)
Selected AbstractsReversal of Fortunes or Continued Success?INTERNATIONAL MIGRATION REVIEW, Issue 2 2010Cohort Differences in Education, Earnings of Childhood Immigrants Using several years of Canadian census data, this study examines cohort differences in educational attainment and earnings among childhood immigrants who arrived in Canada between 1960 and 1989. Successive cohorts of childhood immigrants had increasingly higher university completion rates than their Canadian-born peers by age 25,34. We find that this lead was tempered by declining earnings of immigrant parents relative to Canadian-born parents, particularly among the 1980s cohort. Despite rising university completion rates, wages of male (but not female) childhood immigrants lagged behind those of their Canadian-born peers. This gap can be accounted for largely by the rising share of members of racial minority groups and the decreasing incidence of full-time employment. [source] Sharp developmental thresholds defined through bistability by antagonistic gradients of retinoic acid and FGF signalingDEVELOPMENTAL DYNAMICS, Issue 6 2007Albert Goldbeter Abstract The establishment of thresholds along morphogen gradients in the embryo is poorly understood. Using mathematical modeling, we show that mutually inhibitory gradients can generate and position sharp morphogen thresholds in the embryonic space. Taking vertebrate segmentation as a paradigm, we demonstrate that the antagonistic gradients of retinoic acid (RA) and Fibroblast Growth Factor (FGF) along the presomitic mesoderm (PSM) may lead to the coexistence of two stable steady states. Here, we propose that this bistability is associated with abrupt switches in the levels of FGF and RA signaling, which permit the synchronized activation of segmentation genes, such as mesp2, in successive cohorts of PSM cells in response to the segmentation clock, thereby defining the future segments. Bistability resulting from mutual inhibition of RA and FGF provides a molecular mechanism for the all-or-none transitions assumed in the "clock and wavefront" somitogenesis model. Given that mutually antagonistic signaling gradients are common in development, such bistable switches could represent an important principle underlying embryonic patterning. Developmental Dynamics 236:1495,1508, 2007. © 2007 Wiley-Liss, Inc. [source] Genetic evidence for `leaky' cohorts in the semivoltine stonefly Peltoperla tarteri (Plecoptera: Peltoperlidae)FRESHWATER BIOLOGY, Issue 3 2002ALICIA S. SCHULTHEIS 1.,Genetic techniques are being used increasingly to address questions about dispersal and gene flow of freshwater invertebrates. However, population genetic structure can be affected by factors other than dispersal. Many stream insects have long life cycles that result in the simultaneous existence of multiple cohorts throughout the larval development period. If larval development is fixed, successive cohorts may be reproductively isolated and, as a result, genetically distinct. In such cases, significant levels of genetic differentiation between cohorts could confound estimates of dispersal based on population genetic structure. 2.,Peltoperla tarteri is a stonefly that can be abundant in Appalachian headwater streams. Although P. tarteri is univoltine at the type locality (Big Paint Hollow, WV, U.S.A.), the study populations in southwestern Virginia, U.S.A., were semivoltine. This semivoltine life cycle results in the simultaneous existence of multiple cohorts with the potential for significant genetic differentiation among them. 3.,Levels of genetic differentiation among P. tarteri cohorts were analysed with mitochondrial DNA (mtDNA) sequence data from the non-coding origin of replication or `control' region from 93 individuals from two successive cohorts (collected in 1998 and 1999). 4.,Analysis of molecular variance (AMOVA) indicated no genetic differentiation among cohorts (FST=0.0), and gene flow among cohorts was very high (Nm=,). 5.,High levels of gene flow among cohorts suggest that larval development of P. tarteri is not fixed. Gene flow among cohorts most likely occurs as a result of a cohort split in which some individuals complete development in one or three years instead of two. [source] Between-year variation of MHC allele frequencies in great reed warblers: selection or drift?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2004H. Westerdahl Abstract The major histocompatibility complex (MHC) genes are extremely polymorphic and this variation is assumed to be maintained by balancing selection. Cyclic interactions between pathogens and their hosts could generate such selection, and specific MHC alleles or heterozygosity at certain MHC loci have been shown to confer resistance against particular pathogens. Here we compare the temporal variation in allele frequencies of 23 MHC class I alleles with that of 23 neutral microsatellite markers in adult great reed warblers (a passerine bird) in nine successive cohorts. Overall, the MHC alleles showed a significantly higher variation in allele frequencies between cohorts than the microsatellite alleles, using a multi-variate genetic analysis (amova). The frequency of two specific MHC alleles, A3e (P = 0.046) and B4b (P = 0.0018), varied more between cohorts than expected from random, whereas none of the microsatellite alleles showed fluctuations exceeding the expectation from stochastic variation. These results imply that the variation in MHC allele frequencies between cohorts is not a result of demographic events, but rather an effect of selection favouring different MHC alleles in different years. [source] Successful Aging: Implications for Oral HealthJOURNAL OF PUBLIC HEALTH DENTISTRY, Issue 4 2000H. Asuman Kiyak PhD ABSTRACT The past few years have seen a growing emphasis in gerontology on the concept of "successful" or "robust" aging. This represents a major paradigm shift in the field from a focus on declines in physical and social functioning, assumptions of the aging process as a downward spiral, and studies on how to manage these declines. Leading the way toward this new perspective on aging, the MacArthur Studies of Successful Aging asked the fundamental question: "What genetic, biomedical, behavioral, and social factors are crucial to maintaining health and functional capacities in the later years?" These studies examined longitudinally a large cohort of independent elders on several physical, cognitive, emotional, and social parameters. Other researchers have focused on the theme of robust aging; however, common predictors have emerged, such as remaining active physically and cognitively, maintaining social contacts, and avoiding disease. This research is timely, given the expanding population of the oldest old, and with successive cohorts demonstrating the "compression of morbidity" phenomenon. Such a paradigm shift is critical in geriatric dentistry as well, where successful aging is evident in the growing number of older adults who have retained their natural dentition into advanced old age. This presentation draws parallels between successful aging at the systemic and oral health levels, with illustrations from epidemiologic studies that demonstrate trends in improved health and quality of life among newer cohorts of older adults. [source] Cohort Reproductive Patterns in Low-Fertility CountriesPOPULATION AND DEVELOPMENT REVIEW, Issue 1 2001Tomas Frejka This account reports on a project in progress that aims to obtain a comprehensive picture of contemporary fertility levels and trends in 27 low-fertility countries. Cohort analysis is applied to review the fertility experience of women born from the 1930s through the 1970s. This choice of dates ensures that not only completed fertility but also the fertility patterns of women in the midst of or near the onset of their reproductive period are examined. In most of the 27 countries, completed fertility of successive cohorts has been declining. It appears plausible that the trends discerned in the analysis will continue in the foreseeable future. For these trends to be reversed, women who are about to enter or who are in the midst of their reproductive periods would have to adopt fertility patterns markedly different from those of women born in the 1960s and 1970s. [source] Trends in incidence and mortality in rheumatoid arthritis in Rochester, Minnesota, over a forty-year periodARTHRITIS & RHEUMATISM, Issue 3 2002Michele F. Doran Objective To determine time trends in the epidemiology of rheumatoid arthritis (RA) in a population-based cohort. Methods An inception cohort of residents of Rochester, Minnesota ,18 years of age who first fulfilled the American College of Rheumatology 1987 criteria between January 1, 1955 and December 31, 1994 (applied retrospectively, as appropriate) was assembled and followed up until January 1, 2000. Incidence rates were estimated and were age- and sex-adjusted to the 1990 white population of the US. A birth cohort analysis was performed, and survival rates over time were examined. Results The incidence cohort comprised 609 patients, 445 (73.1%) of whom were female and 164 (26.9%) were male, with a mean age at incidence of 58.0 years. The overall age- and sex-adjusted annual incidence of RA among Rochester, Minnesota, residents ,18 years of age was 44.6/100,000 population (95% confidence interval 41.0,48.2). While the incidence rate fell progressively over the 4 decades of study, from 61.2/100,000 in 1955,1964, to 32.7/100,000 in 1985,1994, there were indications of cyclical trends over time. Birth cohort analysis showed diminishing incidence rates through successive cohorts following a peak in the 1880,1890 cohorts. Incidence rates increased with age until age 85, but peaked earlier in women than in men. The survival rate in RA patients was significantly lower than the expected rate in the general population (P < 0.001), and no improvement was noted over time. Conclusion The secular trends demonstrated in this study population, including the progressive decline in the incidence of RA over the last 40 years, suggest that an environmental factor may play a role in the etiology of RA. [source] Phase I pharmacokinetic study of the vascular endothelial growth factor receptor tyrosine kinase inhibitor vatalanib (PTK787) plus imatinib and hydroxyurea for malignant gliomaCANCER, Issue 10 2009David A. Reardon MD Abstract BACKGROUND: This study determined the maximum tolerated dose (MTD) and dose-limiting toxicities (DLT) of the oral vascular endothelial growth factor receptor (VEGFR) inhibitor, vatalanib, when administered with imatinib and hydroxyurea on a continuous daily schedule among recurrent malignant glioma patients. METHODS: All patients received 500 mg of hydroxyurea twice daily. Imatinib was dosed at 400 mg per day for patients not taking enzyme-inducing antiepileptic drugs (EIAEDs; stratum A) and at 500 mg twice-a-day for patients taking EIAEDs (stratum B). Vatalanib was escalated from 500 mg to 1250 mg twice daily in successive cohorts, independently for each stratum. Pharmacokinetics of each drug were assessed. RESULTS: A total of 37 recurrent patients, 34 (92%) with glioblastoma and 3 (8%) with grade 3 malignant glioma, were enrolled. Nineteen patients (51%) were taking EIAEDs. The MTD of vatalanib for all patients was 1000 mg twice-a-day. DLTs were hematologic, gastrointestinal, renal, and hepatic. No patients developed intracranial hemorrhage. Concurrent administration of imatinib and hydroxyurea did not affect vatalanib exposure, but EIAEDs decreased vatalanib and imatinib plasma exposures. CONCLUSIONS: Vatalanib doses up to 1000 mg twice-a-day combined with imatinib and hydroxyurea were well tolerated. Strategies to target tumor blood vessel endothelial cells and pericytes by inhibiting VEGFR and platelet-derived growth factor, respectively, were safe among recurrent malignant glioma patients and may enhance antiangiogenesis activity. Cancer 2009. © 2009 American Cancer Society. [source] Birth Cohort Effects on Incidence of Lung Cancers: A Population-based Study in Nagasaki, JapanCANCER SCIENCE, Issue 10 2000Hiroshi Soda Smoking prevalence remains high (around 60%) among Japanese males, but smoking initiation among males born in the 1930s decreased by approximately 10% due to economic difficulties following World War II. The present study was designed to examine whether this temporary decline in smoking initiation influenced the subsequent incidence of lung cancers, especially adenocarcinoma. Trends of lung cancer incidence by histological type in both sexes were investigated using data from the population-based cancer registry in Nagasaki, Japan, from 1986 through 1995. During this period, 5668 males and 2309 females were diagnosed as having lung cancer, and the overall incidence of lung cancers among both sexes remained stable. However, males aged 55,59 years showed a decrease in the age-specific incidence of adenocarcinoma and squamous-cell carcinoma (P < 0.05 and P < 0.01, respectively). In birth cohort analyses, the incidence of adenocarcinoma and squamous-cell carcinoma was lower in the 1935,1939 birth male cohort than in the successive cohorts. The incidence of lung cancers among females with low smoking prevalence did not change with birth cohort. The low smoking initiation among the 1935,1939 birth male cohort appeared to have resulted in a decreased incidence of adenocarcinoma and squamous cell carcinoma among middle-aged Japanese males. The present study suggests that smoking prevention has an effect in reducing the incidence of lung adenocarcinoma, as well as squamous-cell carcinoma, among smokers. [source] | ||||||||||||||||