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Biomedical subjects

N G Bennett

Publications and source records attributed to N G Bennett.

12 recordsLinked to original sources
PubMed2001

Birth weight and income: interactions across generations.

This paper attempts to answer a series of questions regarding the interaction of income and birth weight across generations. First, does the effect of the income of a mother during her pregnancy on her infant's birth weight depend on the family's birth weight history (genetic predisposition)? Second, does the effect of low birth weight status on adult life chances depend on income during early childhood? These questions have implications for the way we envision the biological and social worlds as interacting across generations. To address these issues, this study uses intergenerational data from the Panel Study of Income Dynamics, survey years 1968 through 1992. Results of sibling comparisons (family-fixed-effects models) demonstrate that maternal income has a significant impact on birth weight for those infants who are already at high risk hereditarily (i.e., who have a low birth weight parent). However, it is not clear whether income acts as a developmental buffer for low birth weight infants as their lives progress. These findings suggest the existence of biosocial interactions between hereditary predisposition and socio-economic environment.

Adolescent↗
PubMed1997

The effects of poverty on child health and development.

Poverty has been shown to negatively influence child health and development along a number of dimensions. For example, poverty-net of a variety of potentially confounding factors-is associated with increased neonatal and postneonatal mortality rates, greater risk of injuries resulting from accidents or physical abuse/neglect, higher risk for asthma, and lower developmental scores in a range of tests at multiple ages. Despite the extensive literature available that addresses the relationship between poverty and child health and development, as yet there is no consensus on how poverty should be operationalized to reflect its dynamic nature. Perhaps more important is the lack of agreement on the set of controls that should be included in the modeling of this relationship in order to determine the "true" or net effect of poverty, independent of its cofactors. In this paper, we suggest a general model that should be adhered to when investigating the effects of poverty on children. We propose a standard set of controls and various measures of poverty that should be incorporated in any study, when possible.

Asthma↗
PubMed1995

The influence of nonmarital childbearing on the formation of first marriages.

We document a negative association between nonmarital childbearing and the subsequent likelihood of first marriage in the United States, controlling for a variety of potentially confounding influences. Nonmarital childbearing does not appear to be driven by low expectations of future marriage. Rather, it tends to be an unexpected and unwanted event, whose effects on a woman's subsequent likelihood of first marriage are negative on balance. We find that women who bear a child outside marriage and who receive welfare have a particularly low probability of marrying subsequently, although there is no evidence that AFDC recipients have lower expectations of marriage. In addition, we find no evidence that stigma associated with nonmarital childbearing plays an important role in this process or that the demands of children significantly reduce unmarried mothers' time for marriage market activities.

Adolescent↗
PubMed1990

Modeling American marriage patterns.

"This article investigates the application of the three-parameter, Coale-McNeil marriage model and some related hyperparameterized specifications to data on the first marriage patterns of American women. Because the model is parametric, it can be used to estimate the parameters of the marriage process for cohorts that have yet to complete their first marriage experience. Empirical evidence from three surveys is reported on the ability of the model to replicate and project observed marriage behavior. The results indicate that the model can be a useful tool for analyzing cohort marriage data and that recent cohorts are showing relatively strong proclivities to both delay and forego marriage. Consistent with earlier work, the results also indicate that education is a powerful covariate of the timing of first marriage and that race is a powerful covariate of its incidence." Data are from the U.S. Current Population Survey for 1976 and 1985 and Cycle III of the National Survey of Family Growth for 1982.

Americas↗
PubMed1984

Mortality estimation from registered deaths in less developed countries.

Age-specific population growth rates were introduced to demographic analysis in earlier work by Bennett and Horiuchi (1981) and Preston and Coale (1982). In this paper, we derive a method which uses these growth rates to transform what may be a set of incompletely recorded deaths by age into a life table that accurately reflects the true mortality experience of the population under study. The method does not rely on the assumption of stability and, for example, in contrast to intercensal cohort survival techniques, is simple to implement when presented with nontraditional intercensal interval lengths. Thus we can obtain mortality estimates for less developed countries with defective data, despite departures from stability. Further, we assess the sensitivity of the method to violations in various assumptions underlying the procedure: error in estimated growth rates, existence of non-zero net intercensal migration, age dependence in the completeness of death registration, and misreporting of age at death and age in the population. We demonstrate the use of the method in an application to data referring to Argentine females during the period 1960 to 1970.

Adolescent↗
PubMed1977

Sex selection with biased technologies and its effect on the population sex ratio.

Current biomedical research on sex selection techniques may soon offer couples the opportunity to choose the sex of their children with greater certainty. A technique planned for marketing by mid-1978 can increase the probability of bearing a son to as much as 0.90. However, couples who wish to improve their chances of bearing a daughter have no such opportunity. The purpose of this paper is two-fold. First, a decision-making model is provided which describes how couples should choose among alternative sex-selection methods so as to maximize the probability of bearing their desired number of sons and daughters. Second, the effect of the widespread use of sex-selection techniques on the population sex ratio is explored. It is shown that even if populations have unbiased sex preferences, or sex preferences biased towards daughters, the use of biased sex-selection technologies may result in very high population sex ratios.

Belgium↗
PubMed1977

Sampling variability of own-children fertility estimates.

This paper develops methodology for estimating standard errors and confidence intervals for own-children estimates of age-specific birth rates and total fertility rates. The methodology applies to systematic samples of households, which are treated as simple random samples of women. The assumption of simple random selection, together with the treatment of sample subgroup size and reverse-survival ratios as constants instead of random variables, imply that sampling variability is slightly underestimated. The methodology is applied illustratively to fertility estimates based on the 1970 census of the Philippines.

Birth Rate↗
PubMed1974

The identification of intermediates in the reaction of pig heart lactate dehydrogenase with its substrates.

Pig heart lactate dehydrogenase was studied in the direction of pyruvate and NADH formation by recording rapid changes in extinction, proton concentration, nucleotide fluorescence and protein fluorescence. Experiments measuring extinction changes show that there is a very rapid formation of NADH within the first millisecond and that the amplitude of this phase (phase 1) increases threefold over the pH range 6-8. A second transient rate (phase 2) can also be distinguished (whose rate is pH-dependent), followed by a steady-state rate (phase 3) of NADH production. The sum of the amplitudes of the first two phases corresponds to 1mol of NADH produced/mol of active sites of lactate dehydrogenase. Experiments that measured the liberation of protons by using Phenol Red as an indicator show that no proton release occurs during the initial very rapid formation of NADH (phase 1), but protons are released during subsequent phases of NADH production. Fluorescence experiments help to characterize these phases, and show that the very rapid phase 1 corresponds to the establishment of an equilibrium between E(NAD) (Lactate) right harpoon over left harpoon H(+)E(NADH) (Pyruvate). This equilibrium can be altered by changing lactate concentration or pH, and the H(+)E(NADH) (Pyruvate) species formed has very low nucleotide fluorescence and quenched protein fluorescence. Phase 2 corresponds to the dissociation of pyruvate and a proton from the complex with a rate constant of 1150s(-1). The observed rate constant is slower than this and is proportional to the position of the preceding equilibrium. The E(NADH) formed has high nucleotide fluorescence and quenched protein fluorescence. The reaction, which is rate-limiting during steady-state turnover, must then follow this step and be involved with dissociation of NADH from the enzyme or some conformational change immediately preceding dissociation. Several inhibitory complexes have also been studied including E(NAD+) (Oxamate) and E(NADH) (Oxamate') and the abortive ternary complex E(NADH) (Lactate). The rate of NADH dissociation from the enzyme was measured and found to be the same whether measured by ligand displacement or by relaxation experiments. These results are discussed in relation to the overall mechanism of lactate dehydrogenase turnover and the independence of the four binding sites in the active tetramer.

Acid-Base Equilibrium↗
PubMed1973

The kinetics of the interconversion of intermediates of the reaction of pig muscle lactate dehydrogenase with oxidized nicotinamide-adenine dinucleotide and lactate.

Oxamate competes with pyruvate for the substrate binding site on the E(NADH) complex of pig skeletal muscle lactate dehydrogenase. When this enzyme was mixed with saturating concentrations of NAD(+) and lactate in a stopped-flow rapid-reaction spectrophotometer there was no transient accumulation of enzyme complexes with the reduced nucleotide. The steady-state rate of formation of free NADH was reached within the dead-time of the instrument (3ms). When oxamate was added to inhibit the steady state and to uncouple the equilibration: [Formula: see text] through the rapid formation of E(NADH) (Oxamate), the rate of formation of E(NADH) could be measured by observation of the first turnover. This pH-dependent transient is controlled by the rate of dissociation of pyruvate and the fraction of the enzyme in the form E(NADH) (Pyruvate).

Animals↗
PubMed1969

A substate-induced conformation change in the reaction of alkaline phosphatase from Escherichia coli.

1. Benzyl phosphonates were prepared and their potentialities as chromophoric reagents for the exploration of the substrate-binding site of Escherichia coli alkaline phosphatase were investigated. 4-Nitrobenzylphosphonate is a competitive inhibitor of the enzyme. 2-Hydroxy-5-nitrobenzylphosphonate changes its spectrum on binding to the enzyme. This spectral change is reversed when the phosphonate is displaced from the enzyme by substrate. 2. The kinetics of the reaction of 2-hydroxy-5-nitrophenylphosphonate were studied by the stopped-flow and the temperature-jump techniques. It was found that the combination of the phosphonate with the enzyme occurred in two successive and reversible steps: enzyme-phosphonate complex-formation followed by rearrangement of the complex. The spectral change is associated with the rearrangement. At pH8 in 1m-sodium chloride at 22 degrees the rate constant is 167sec.(-1) for the rearrangement of the initially formed binary complex and is 18sec.(-1) for the reverse process. 3. It has previously been proposed that the reactions of phosphatase with its substrates include a distinct step between enzyme-substrate combination and chemical catalysis. The rate constant involved could be predicted but not measured from experiments with substrates. The value for the rate constant measured from the rate of the enzyme-phosphonate rearrangement is in excellent agreement with the predicted value. A model for the reaction mechanism is proposed that includes a conformation change in response to phosphate ester binding before phosphate transfer from substrate to enzyme.

Alkaline Phosphatase↗
PubMedDate not supplied

Race and the inheritance of low birth weight.

This paper uses intergenerational data from the Panel Study of Income Dynamics (PSID) to address the black-white difference in propensities toward low birth weight (LBW). We determine that socioeconomic conditions account for some variation in low birth weight across race. Further, while race differences in the risk of low birth weight cannot be explained entirely, we find that the inheritance of parental birth weight status dramatically reduces the black-white gap in low birth weight. Intergenerational legacies of poor infant health explain the largest share of racial disparities in filial birth weight. We then try to assess whether this intergenerational transmission of low birth weight is indeed genetic by using grandparent-fixed effects models to factor out, to a great extent, family socioeconomic circumstances. We find that even within this framework, both father's and mother's birth weight status have an important impact on filial outcomes. However, the degree of inheritance is weaker for African Americans than for other races. Finally, we theorize that the importance of paternal birth weight status implies a genetic association that does not work through the uterine environment but rather through the fetus itself.

Adolescent↗