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Biomedical subjects

T B Gage

Publications and source records attributed to T B Gage.

At least 19 recordsLinked to original sources
PubMed2001

Genetic and environmental correlations between various anthropometric and blood pressure traits among adult Samoans.

Shared polygenic effects (i.e., pleiotropy) are assumed to exist for such obesity-related phenotypes as blood pressure and adiposity. It is possible to identify these shared genetic effects through bivariate genetic analyses. This analysis of 1,342 adult Samoans, across 801 pedigrees, indicates that significant heritable components (P < 0.05) ranging from 29-58% exist for weight, height, systolic blood pressure, diastolic blood pressure, triceps skinfold, subscapular skinfold, body mass index, and sum of skinfolds. In general, the anthropometric measurements share additive genetic effects, as do the anthropometric measures, with blood pressure. Heritabilities for central fat distribution are not significant in this population, which could be due to a lack of power. On the other hand, heritabilities have been found in Hispanics; hence the genes responsible for central fat distribution may not be evenly distributed among populations.

Adult↗
PubMed1998

Variability of birth-weight distributions by sex and ethnicity: analysis using mixture models.

Birth weight is the most important proximate determinant of the level of infant mortality. However, the association between birth weight and infant mortality is not constant among populations. For example, the mortality of African American infants is lower at low birth weight but higher at high birth weight compared with European American infants. One possible explanation is that birth cohorts are heterogeneous even after controlling for birth weight, ethnicity, sex, and multiple births. The analyses presented here use Gaussian mixture models to explore the interpopulation variation in the shape of the birth-weight distribution for evidence of intrapopulation heterogeneity. The results suggest that a two-component mixture model provides an excellent description of human birth-weight distributions. Further statistical analyses of sex and ethnic differences indicate (1) that the birth-weight distributions and heterogeneity within the distribution vary between the sexes and among ethnic groups and (2) that one specific component is more closely associated with the overall level of infant mortality. The results support the hypothesis that birth cohorts can consist of two or more subpopulations at differential risk of mortality. Differences in the subpopulation composition of birth cohorts (i.e., differences in the level of heterogeneity among the various ethnic groups) might partially explain the interethnic variation in birth-weight-specific mortality. Further development of these mixture models should provide important additional information concerning the biological, environmental, and social determinants of birth weight and infant mortality.

Black or African American↗
PubMed1994

Population variation in cause of death: level, gender, and period effects.

The trends in 13 cause of death categories are examined with respect to expectation of life, sex differences, and period effects while misclassification of cause of death is controlled. The results suggest that as mortality declines, 1) the increasingly U-shaped age pattern of mortality is a period effect associated with the infectious diseases, 2) the risks of both overall infectious and degenerative causes of death decline, and 3) infectious disease mortality declines more in males, while degenerative disease mortality declines more in females. Finally, the model shows that some contemporary populations are approaching the limits of reduction in mortality during infancy, childhood, and young adulthood. Past declines in the degenerative diseases, however, suggest that mortality may continue to decline.

Adult↗
PubMed1994

Nutrition and the variation in level and age patterns of mortality.

We examine the associations between nutrition and mortality at the national level. Altogether four aspects of this association are explored: (1) total calories with expectation of life, (2) dietary composition with expectation of life, (3) total calories with the age patterns of mortality, and (4) dietary composition with the age patterns of mortality. The data consist of life tables and national food balance sheets for 341 populations from 96 countries. A preliminary principal components analysis conducted on the dietary composition data yields three dietary components: (1) the overall quality and quantity of the diet, (2) the relative contribution of carbohydrates versus fats, and (3) the relative contribution of fats versus proteins. The results indicate that expectation of life at birth increases with total calories, with overall quality and quantity of the diet, and with the ratio of fats to proteins. The ratio of carbohydrates to fats is negatively associated with level of mortality. However, evidence indicates that the main effect of the ratio of fats to proteins is reversed when diets are high in quality and that all the effects tend to saturate at high nutrient availability. Variation in nutrition is also strongly associated with the international variation in age patterns of mortality. For example, when expectation of life is held constant, populations with higher quality diets tend to have lower childhood mortality and higher adult mortality. The results indicate that nutritional patterns are highly correlated with much of the worldwide variation in mortality and may be a useful criterion for selecting or predicting the best suited model life table for use on a particular population.

Adolescent↗
PubMed1993

Some laws of mortality: how well do they fit?

The goodnesses of fit over the entire life span of four models of mortality are compared using life tables from Australia and the United States. The results indicate that the five-parameter Siler model fits considerably better than the more complex eight-parameter Heligman-Pollard and Mode-Busby models. On the other hand, the ten-parameter model proposed by Mode and Jacobson fits human mortality patterns better than the Siler model. We conclude that the Heligman-Pollard and Mode-Busby models are probably misspecified. Additional research is necessary to determine (1) whether the Heligman-Pollard model can be improved by specifying it as a true hazard model and (2) whether the respecified Heligman-Pollard and Mode-Jacobson models are statistically robust, particularly with abridged life tables.

Adolescent↗
PubMed1991

Reproductive factors affecting survivorship in captive Callitrichidae.

Efforts to breed Callitrichidae in captivity have resulted in high fertility accompanied by high infant mortality. This paper investigates the relationship between reproductive characteristics and survivorship in the Oak Ridge and Associated Universities (ORAU) callitrichid colony. Records of 2,834 individuals were analyzed using Cox Proportional Hazards regression to investigate factors affecting infant survivorship. Species and birth cohort were found to have a significant (P less than 0.05) effect on survivorship. Litter size also was an important factor in determining survivorship. Individuals born into singlet and twin litters had significantly (P less than 0.001) higher survivorship than triplets. Factors which affect survivorship perinatally (0-1 months of age), prior to breeding age and subsequent to the first month of life were then investigated. Litter size was a significant (P less than 0.05) factor in determining survivorship perinatally, with twins having significantly higher survivorship than both singlets and triplets. After the first month of life, litter size no longer showed a significant effect on survivorship. Records of 145 dams were analyzed using the same procedures to investigate reproductive characteristics associated with survivorship. Age at first litter showed a significant (P less than 0.01) positive relationship with dam survivorship. These results suggest various factors affect survivorship at specific temporal points during development, and also suggest selection for survivorship perinatally to be strongly associated with litter size, possibly through sibling competition and maternal effects.

Animals↗
PubMed1991

Effects of age and gender on the location and orientation of the foramen magnum in rhesus macaques (Macaca mulatta).

Endocasts from 378 rhesus macaque skulls from the Cayo Santiago skeletal collection were measured to determine the effects of age and gender on the position and orientation of the foramen magnum. The foramen magnum migrates from a rostral to a caudal position and its angle changes during postnatal development. The angles and relative positions of the foramen magnum are similar for both genders of infants and for both genders of adults. However, analyses of linear response and plateau (LRP) functions reveal significant differences between males and females in the timing of reorientation of the angle and migration of the foramen magnum. The mean adult angle and relative position of the foramen magnum are reached by 4.7 years in females, but they do not achieve their adult values until 7.1 years in males. A similar pattern is observed for the brainstem region of the basicranium. Mean adult lengths of the brainstem region are reached at 5.2 years in females and 7.1 years in males. The relationships between cranial capacity, the growth pattern of the brainstem, and the pattern of change for the angle and the relative position of the foramen magnum are examined. Quantification of the effects of age and gender on the location of the foramen magnum in a large sample of endocasts from one species of higher primate has potential implications for research on human development, and for interpretation of juvenile specimens in the hominid fossil record.

Age Factors↗
PubMed1990

Variation and classification of human age patterns of mortality: analysis using competing hazards models.

The structure of variation in human mortality patterns is explored using a five-parameter competing hazards model and standard multivariate taxonomic procedures. The data consist of 281 national life tables representing a wide range of environmental and cultural regions of the world. A general or average age pattern of mortality was generated for the entire sample using multiple regression procedures. A K mean cluster analysis conducted on the residuals of the regression analysis identified seven distinct models of mortality that differ in characteristic ways from the general pattern. Four of the seven clusters have age patterns of mortality similar to the north, east, south, and west regions of the Coale and Demeny model life tables. The remaining three clusters represent regions of the world and age patterns of mortality that are not represented in the Coale and Demeny model life tables.

Age Factors↗
PubMed1988

Mathematical hazard models of mortality: an alternative to model life tables.

A five-parameter competing hazard model of the age pattern of mortality is described, and methods of fitting it to survivorship, death rate, and age structure data are developed and presented. The methods are then applied to published life table and census data to construct life tables for a Late Woodland population, a Christian period Nubian population, and the Yanomama. The advantage of this approach over the use of model life tables is that the hazard model facilitates life-table construction without imposing a particular age pattern of mortality on the data. This development makes it possible to use anthropological data to extend the study of human variation in mortality patterns to small populations.

Adolescent↗
PubMed1984

Division synchrony and the dynamics of microbial populations: a size-specific model.

A discrete, environmentally coupled, size-specific model of microbial population dynamics in continuous culture is presented. It is mathematically simpler than other models based on similar assumptions and lends itself to numerical and analytic solutions. It displays several phenomena which have been reported in the experimental literature but which are not well understood; specifically, a loose relationship between biomass and numbers (i.e., a time lag between mass growth and cell division) and a critical damping of biomass while numbers continue to oscillate. In addition, the model provides several new predictions: The stable biomass distribution is independent of the environmental factors considered in the model and uniformly distributes the biomass among the size classes. The rate of approach to stability and the frequency of waves through the size distributions are a function of the flow rate and the variance in rate of growth and size at division. The model should provide a useful basis for studying the effects of size specificity on the dynamics of microbial populations cultured in chemostats.

Bacteria↗