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Biomedical subjects

S E Maxwell

Publications and source records attributed to S E Maxwell.

18 recordsLinked to original sources
PubMed2000

Structural differences in parent and child reports of children's symptoms of depression and anxiety.

Two cohorts of public elementary school children and their parents (assessed 3 years apart) completed child and parent forms of the Children's Depression Inventory (CDI) and the Revised Children's Manifest Anxiety Scale (RCMAS). Assessments were conducted twice, once during the fall (N = 562) and again during the spring (N = 630) of the 6th grade. Factor analyses revealed 3 factors for each measure. Two of the 3 parent CDI factors manifested some degree of congruence with their counterparts from the child CDI. Similarly, 2 of the 3 RCMAS factors were somewhat congruent across informant types. Differences between parent and child factor structures suggest that parents' and children's reports focus on somewhat different aspects of child psychopathology, and they can make qualitatively different contributions to the multiaxial assessment of children.

Adolescent↗
PubMed2000

The proof of the pudding: an illustration of the relative strengths of null hypothesis, meta-analysis, and Bayesian analysis.

Some methodologists have recently suggested that scientific psychology's over-reliance on null hypothesis significance testing (NHST) impedes the progress of the discipline. In response, a number of defenders have maintained that NHST continues to play a vital role in psychological research. Both sides of the argument to date have been presented abstractly. The authors take a different approach to this issue by illustrating the use of NHST along with 2 possible alternatives (meta-analysis as a primary data analysis strategy and Bayesian approaches) in a series of 3 studies. Comparing and contrasting the approaches on actual data brings out the strengths and weaknesses of each approach. The exercise demonstrates that the approaches are not mutually exclusive but instead can be used to complement one another.

Bayes Theorem↗
PubMed2000

Sample size and multiple regression analysis.

Despite the development of procedures for calculating sample size as a function of relevant effect size parameters, rules of thumb tend to persist in designs of multiple regression studies. One explanation for their persistence may be the difficulty in formulating a reasonable a priori value of an effect size to be detected. This article presents methods for calculating effect sizes in multiple regression from a variety of perspectives and also introduces a new method based on an exchangeability structure among predictor variables. No single method is deemed superior, but rather examples show that a combination of methods is likely to be most valuable in many situations. A simulation provides a 2nd explanation for why rules of thumb for choosing sample size have persisted but also shows that the outcome of such underpowered studies will be a literature consisting of seemingly contradictory results.

Child↗
PubMed2000

Prenatal maternal predictors of cognitive and emotional delays in children of adolescent mothers.

The present study examined relationships among prenatal characteristics of 121 adolescent mothers-including cognitive readiness for parenting, intelligence, social support, and personal adjustment-and intellectual-linguistic development, social-emotional functioning, and adaptive behavior in their children at three years of age. Only 28% of the children scored within normal ranges on all three types of outcomes. Intellectual and linguistic delays were predicted best by prenatal measures of maternal Performance IQ and social support from extended family. Socioemotional problems were predicted best by maternal internalizing problems and social support from partner and friends. Adaptive behavior was associated with parenting style. Implications for the early identification of high-risk children--and associated intervention programs--are discussed.

Adaptation, Psychological↗
PubMed1997

Cumulative and compensatory effects of competence and incompetence on depressive symptoms in children.

The authors tested 5 hypotheses from a competency-based model of child depression using classification and regression tree analysis. The authors obtained measures of 5 domains of competency (i.e., academic competence, social acceptance, sports competence, physical attractiveness, and behavioral conduct) and depressive symptoms that were derived from parent, teacher, peer, and self-reports on 1,063 3rd- and 6th-grade children. Results suggested that (a) multiple domains of competence related to depressive symptoms, (b) significant others' positive evaluations in multiple domains have a cumulative inverse relation to depressive symptoms, (c) negative evaluations in multiple domains have a cumulative but positive relation to depressive symptoms, (d) positive evaluations in one domain somewhat compensate for negative evaluations in another domain, and (e) negative evaluations in one domain offset positive evaluations in another domain.

Child↗
PubMed1996

COOH-terminal processing of nascent polypeptides by the glycosylphosphatidylinositol transamidase in the presence of hydrazine is governed by the same parameters as glycosylphosphatidylinositol addition.

Proteins anchored to the cell membrane via a glycosylphosphatidylinositol (GPI) moiety are found in all eukaryotes. After NH2-terminal peptide cleavage of the nascent protein by the signal peptidase, a second COOH-terminal signal peptide is cleaved with the concomitant addition of the GPI unit. The proposed mechanism of the GPI transfer is a transamidation reaction that involves the formation of an activated carbonyl intermediate (enzyme-substrate complex) with the ethanolamine moiety of the preassembled GPI unit serving as a nucleophile. Other nucleophilic acceptors like hydrazine (HDZ) and hydroxylamine have been shown to be possible alternate substrates for GPI. Since GPI has yet to be purified, the use of readily available nucleophilic substitutes such as HDZ and hydroxylamine is a viable alternative to study COOH-terminal processing by the putative transamidase. As a first step in developing a soluble system to study this process, we have examined the amino acid requirements at the COOH terminus for the transamidation reaction using HDZ as the nucleophilic acceptor instead of GPI. The hydrazide-forming reaction shows identical amino acid requirement profiles to that of GPI anchor addition. Additionally, we have studied other parameters relating to the kinetics of the transamidation reaction in the context of rough microsomal membranes. The findings with HDZ provide further evidence for the transamidase nature of the enzyme and also provide a starting point for development of a soluble assay.

Acyltransferases↗
PubMed1996

A defect in glycosylphosphatidylinositol (GPI) transamidase activity in mutant K cells is responsible for their inability to display GPI surface proteins.

The final step in the pathway that provides for glycosylphosphatidylinositol (GPI) anchoring of cell-surface proteins occurs in the lumen of the endoplasmic reticulum and consists of a transamidation reaction in which fully assembled GPI anchor donors are substituted for specific COOH-terminal signal peptide sequences contained in nascent polypeptides. In previous studies we described a human K562 cell mutant line, designated class K, which assembles all the known intermediates of the GPI pathway but fails to display GPI-anchored proteins on its surface membrane. In the present study, we used mRNA encoding miniPLAP, a truncated form of placental alkaline phosphatase (PLAP), in in vitro assays with rough microsomal membranes (RM) of mutant K cells to further characterize the biosynthetic defect in this line. We found that RM from mutant K cells supported NH2-terminal processing of the nascent translational product, preprominiPLAP, but failed to show any detectable COOH-terminal processing of the resulting prominiPLAP to GPI-anchored miniPLAP. Proteinase K protection assays verified that NH2-terminal processed prominiPLAP was appropriately translocated into the endoplasmic reticulum lumen. The addition of hydrazine or hydroxylamine, which can substitute for GPI donors, to RM from wild-type or mutant cells defective in various intermediate biosynthetic steps in the GPI pathway produced large amounts of the hydrazide or hydroxamate of miniPLAP. In contrast, the addition of these nucleophiles to RM of class K cells yielded neither of these products. These data, taken together, lead us to conclude that mutant K cells are defective in part of the GPI transamidase machinery.

Acyltransferases↗
PubMed1995

An active carbonyl formed during glycosylphosphatidylinositol addition to a protein is evidence of catalysis by a transamidase.

Glycosylphosphatidylinositol (GPI) substitution is now recognized to be a ubiquitous method of anchoring a protein to membranes in eukaryotes. The structure of GPI and its biosynthetic pathways are known and the signals in a nascent protein for GPI addition have been elucidated. The enzyme(s) responsible for GPI addition with release of a COOH-terminal signal peptide has been considered to be a transamidase but has yet to be isolated, and evidence that it is a transamidase is indirect. The experiments reported here show that hydrazine and hydroxylamine, in the presence of rough microsomal membranes, catalyze the conversion of the pro form of the engineered protein miniplacental alkaline phosphatase (prominiPLAP) to mature forms from which the COOH-terminal signal peptide has been cleaved, apparently at the same site but without the addition of GPI. The products, presumable the hydrazide or hydroxamate of miniPLAP, have yet to be characterized definitively. However, our demonstration of enzyme-catalyzed cleavage of the signal peptide in the presence of the small nucleophiles, even in the absence of an energy source, is evidence of an activated carbonyl intermediate which is the hallmark of a transamidase.

Acyltransferases↗
PubMed1995

Cleavage without anchor addition accompanies the processing of a nascent protein to its glycosylphosphatidylinositol-anchored form.

Rough microsomal membranes from most mammalian cells, in the presence of a translation system, process nascent proteins with appropriate COOH-terminal signal peptides to their mature glycosylphosphatidylinositol (GPI)-linked forms. The present study, using preprominiplacental alkaline phosphatase as substrate, shows that as much as 10% of the mature product is cleaved correctly but is not linked to GPI. Some of the factors that influence the relative proportions of GPI linked to free mini-placental alkaline phosphatase are the amounts of GPI in the cells and the amino acid substituent at the omega site of the nascent protein. A mechanism for explaining cleavage both with and without GPI addition is presented, which supports a transamidase type of enzyme as the catalyst.

Alkaline Phosphatase↗
PubMed1993

Covariate imbalance and conditional size: dependence on model-based adjustments.

Analysis of covariance (ANCOVA) is frequently recommended to correct for covariate imbalance and to control conditional size of hypothesis tests in randomized designs. Such control, however, depends on the accuracy of the ANCOVA model used to make the adjustments. Examination of residuals together with knowledge of the subject matter are important for obtaining an accurate model. Stratified assignment procedures lessen the dependence of proper control of conditional size on the specific model used in the adjustment procedure.

Age Factors↗
PubMed1993

Personal adjustment during pregnancy and adolescent parenting.

This study examined "naturally occurring differences" in personal adjustment (social competence, behavior problems, and problem-solving skills) among representative groups of pregnant and nonpregnant adolescents and pregnant adults. Differences in parenting stress and parenting style were also assessed among a subsample of adolescent and adult mothers. Finally, the relationship between prenatally assessed personal adjustment and parenting was evaluated in the adolescent mother group. The contributions of important demographic characteristics (socioeconomic status and race) to both between- and within-group relationships were examined. Results suggested that pregnant adolescents were less socially competent and less proficient in their problem solving than their nonpregnant peers and that they exhibited more behavioral problems than a pregnant adult comparison group. Adolescent mothers displayed higher levels of parenting stress and were less responsive and sensitive in interactions with their infants than adult mothers. Support for the hypothesized link between prenatally assessed personal adjustment and adolescent parenting stress was found, whereas no relationship between socioeconomic status and race and parenting stress was established. These results suggest that intervention with young mothers identified during pregnancy as having personal problems might forestall parenting problems that arise during early child rearing.

Adaptation, Psychological↗
PubMed1992

Development of physical ability tests for police officers: a construct validation approach.

A construct validation approach was followed to affirm that 8 physical ability test events were significantly related to two important constructs underlying the job performance of police officers: strength and endurance. A sample of 115 incumbent police officers took 8 physical ability tests and were rated by supervisors on their physical performances in their job. LISREL methods were used to test the model specified, and a reasonable fit was achieved. Portions of the model were tested on an independent sample of 161 applicants; the fit of the model was again acceptable. A nomological network of relationships, in which strength and endurance factors correlated in expected directions with other physiological and demographic variables, was hypothesized and tested. Finally, the data were examined for potential gender differences and bias. Considerable differences were shown between men and women on both test and performance variables, and women would be overpredicted if a common regression line were used for selection purposes.

Adult↗
PubMed1989

Newly synthesized dengue-2 virus nonstructural protein NS1 is a soluble protein but becomes partially hydrophobic and membrane-associated after dimerization.

In a previous paper (G. Winkler, V. B. Randolph, G. R. Cleaves, T. E. Ryan, and V. Stollar, 1988, Virology 162, 187-196) we showed that the newly synthesized dengue-2 virus nonstructural protein, NS1, exists briefly as a monomer and then undergoes dimerization. We demonstrate here that the dimerization of NS1 is associated with a change in hydrophobicity and sedimentability of this protein. Newly synthesized monomeric NS1 is a hydrophilic and water-soluble protein which cannot be pelleted at 75,000 g. After dimerization, however, NS1 showed increased hydrophobicity in a Triton X-114 phase partitioning system and was completely pelletable at 75,000 g; these findings are consistent with NS1 becoming membrane-associated. In experiments in which infected cells were treated with tunicamycin it was shown that the glycosylation of NS1 was not required for either the dimerization or the membrane association.

Animals↗
PubMed1983

Way finding and cognitive mapping in large-scale environments: a test of a developmental model.

First, fourth, and seventh graders (7, 10, and 13 years of age, respectively) were given a series of tasks to assess their spatial competency in and their cognitive mapping of their school campus. Measures of way-finding, landmark, route, and configurational knowledge were obtained and analyzed to (1) assess way-finding skills in the same environment as that in which their cognitive representations were inferred and assessed; (2) determine the validity of the hierarchical model of cognitive mapping development proposed by Siegel and White by examining individual children's performance patterns as well as between-group performance; and (3) investigate the relationship between grade level and familiarity within an environment where familiarity within subsets of the environment varied by grade. Subjects were asked to create and walk three novel and efficient routes, to select photographs of scenes belonging to the three routes, to correctly order and metrically relate those scenes, and to make bearing and distance estimates from four sighting locations to six targets within the environment. Results indicated that all children were extremely competent way finders. Guttman scale analysis revealed that 93% of all children exhibited performance patterns predicted by the proposed model. Further support of the model was found in grade level differences on cognitive mapping measures. Reversals in the developmental trend were found, however, on some portions of the route and configuration measures, and were significantly related to degree of familiarity within the environment.

Adolescent↗
PubMed1983

A comparison of various strength of association measures commonly used in gerontological research.

An increased usage of measures of strength of association or effect size (ES) has been noted in the gerontological literature. Potential confusion could be generated by the fact that different researchers have reported different measures of ES from study to study. This paper involves a comparison of six ES measures commonly used by gerontological researchers as these measures relate to one another in both the analysis of variance and multiple regression models. Three other issues involving ES measures are discussed: (1) the ES of a contrast; (2) orthogonal and nonorthogonal designs; (3) partial Ess.

Age Factors↗
PubMed1981

Nonrandom assignment and the analysis of covariance in aging research.

A technique developed initially by Overall and Woodward for using nonrandom assignment in ANCOVA is reviewed. Though such a technique produces unbiased measures of treatment effects, this is only true when the assumptions of ANCOVA have been met and when group assignment is based on covariate scores. Limitations and potential applications for such a technique in gerontological research are reviewed.

Aged↗