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J L Rodgers

Publications and source records attributed to J L Rodgers.

At least 19 recordsLinked to original sources
PubMed2001

DF-analyses of heritability with double-entry twin data: asymptotic standard errors and efficient estimation.

In this paper we establish the asymptotic distribution of DeFries Fulker (1985) regression estimates for heritability and shared environmental influences with double-entry twin data. A simple formula to estimate the covariance matrix of the coefficients in DF-regressions is provided, and applications to simulated data and Danish twin data show that this method can substantially increase the statistical power of the analyses. We also provide an 'efficient DF-analysis' that yields more precise estimates when additional covariates are included among the explanatory variables.

Adult↗
PubMed2001

Behavior genetic modeling of human fertility: findings from a contemporary Danish Twin Study.

Behavior genetic designs and analysis can be used to address issues of central importance to demography. We use this methodology to document genetic influence on human fertility. Our data come from Danish twin pairs born from 1953 to 1959, measured on age at first attempt to get pregnant (FirstTry) and number of children (NumCh). Behavior genetic models were fitted using structural equation modeling and DF analysis. A consistent medium-level additive genetic influence was found for NumCh, equal across genders; a stronger genetic influence was identified for FirstTry, greater for females than for males. A bivariate analysis indicated significant shared genetic variance between NumCh and FirstTry.

Adult↗
PubMed2000

Genetic and environmental influences on alcohol use: DF analysis of NLSY kinship data.

Research designs to study alcohol use and abuse have included twin, adoption and family history/high risk studies. Results have consistently implied a genetic factor in the aetiology of alcohol abuse. However, less research has been conducted in search of environmental factors. This study uses kinship structure in a large national dataset (the National Longitudinal Survey of Youth) to estimate (using DeFries-Fulker analysis) the extent of the shared genetic, non-shared genetic, shared environmental and non-shared environmental influences on alcohol use. The NLSY kinship sample contained 3890 pairs of cousins, half-siblings, full-siblings and twins between the ages of 14 and 21 in the initial year of the survey (1979). Estimates of heritability (h2) and shared environment (c2) were small to moderate for the entire dataset for both light drinking and heavy drinking behaviour, with h2 estimates slightly higher in each case. Non-shared genetic measures of self-esteem and locus of control accounted for a significant portion of the remaining variance in heavy drinking behaviour. Race and gender patterns showed c2 and h2 estimates that were also small to moderate for both light and heavy drinking behaviour. Significant non-shared effects were found for the White group for heavy drinking behaviour, and for male pairs for both heavy and light drinking behaviour. Additionally, implications and future directions are discussed.

Adolescent↗
PubMed2000

Resolving the debate over birth order, family size, and intelligence.

Hundreds of research articles have addressed the relationship between birth order and intelligence. Virtually all have used cross-sectional data, which are fundamentally flawed in the assessment of within-family (including birth order) processes. Although within-family models have been based on patterns in cross-sectional data, a number of equally plausible between-family explanations also exist. Within-family (preferably intact-family) data are prerequisite for separating within- and between-family causal processes. This observation reframes an old issue in a way that can be easily addressed by studying graphical patterns. Sibling data from the National Longitudinal Survey of Youth are evaluated, and the results are compared with those from other studies using within-family data. It appears that although low-IQ parents have been making large families, large families do not make low-IQ children in modern U.S. society. The apparent relation between birth order and intelligence has been a methodological illusion.

Adolescent↗
PubMed1999

Nature, nurture and first sexual intercourse in the USA: fitting behavioural genetic models to NLSY kinship data.

Fisher (1930) presented both theoretical and empirical results concerning genetic influences on fertility. Since then, only sparse research has been done on the genetics of fertility, although more sophisticated methodogy and data now exist than were available to Fisher. This paper presents a behavioural genetic analysis of age at first intercourse, accounting for genetic, shared environmental, and selected non-shared environmental influences. The data came from the nationally representative National Longitudinal Survey of Youth (NLSY). A newly developed kinship linking procedure was used that identifies links for cousins, half-siblings, full-siblings and twins in the NLSY. The results suggest a genetic influence in the overall dataset, and also among whites and in male-male and opposite-sex pairs. Genetic influences were extremely small or non-existent for blacks and for female-female pairs. Shared environmental influences were small for most subsets of the data, but moderate for female-female pairs. Two specific non-shared environmental influences--self-esteem and locus of control--were ruled out as accounting for any meaningful variance, although other general sources of non-shared environmental influence appear potentially important. Analysis of selected samples from upper and lower tails suggested that genetic influences are important in accounting for both early and late non-virginity. These findings are consistent with work reported by Miller et al. (1999), who used molecular genetic methods. Generally, these findings support the existence of genetic influences and implicate non-shared environmental influences as being important determinants of the timing of loss of virginity among US adolescents and young adults.

Adolescent↗
PubMed1998

Seasonality of induced abortion in North Carolina.

This paper examines the seasonality of induced abortion in North Carolina between 1980 and 1993. Distinct seasonal patterns are found, with a peak in February and a valley in September. These patterns correspond to the implicit seasonality of conceptions associated with the seasonality of birth pattern. One notable difference from the general pattern is among unmarried women aged 18 and younger. They have the February peak and an additional peak in August that may be associated with the summer vacation from school.

Abortion, Induced↗
PubMed1998

Social contagion, adolescent sexual behavior, and pregnancy: a nonlinear dynamic EMOSA model.

Nonlinear dynamic modeling has useful developmental applications. The authors introduce this class of models and contrast them with traditional linear models. Epidemic models of the onset of social activities (EMOSA models) are a special case, motivated by J. L. Rodgers and D. C. Rowe's (1993) social contagion theory, which predict the spread of adolescent behaviors like smoking, drinking, delinquency, and sexuality. In this article, a biological outcome, pregnancy, is added to an earlier EMOSA sexuality model. Parameters quantify likelihood of pregnancy for girls of different sexuality statuses. Five different sexuality/pregnancy models compete to explain variance in national prevalence curves. One finding was that, in the context of the authors' simplified model, adolescent girls have an approximately constant probability of pregnancy across age and time since virginity.

Adolescent↗
PubMed1994

A simple algebraic demonstration of the validity of DeFries-Fulker analysis in unselected samples with multiple kinship levels.

DeFries and Fulker's (Behav. Genet. 15, 467-473, 1985) regression procedure (DF analysis) to estimate c2 and h2 was originally applied to selected twin data. Since then, DF analysis has been applied more broadly in unselected data and with multiple (nontwin) kinship levels. Theoretical work based on the matrix algebra of variance-covariance matrices has shown that estimates of c2 and h2 are unbiased in selected two-group settings. In this article, a simple proof is presented supporting the validity of DF analysis in broader settings. We use scalar algebra to show that parameter estimates of h2 and c2 are unbiased in unselected settings with multiple (more than two) kinship levels. Caveats are offered, and other DF analysis problems are identified.

Bias↗
PubMed1993

Social contagion and adolescent sexual behavior: a developmental EMOSA model.

Epidemic Models of the Onset of Social Activities (EMOSA models) describe the spread of adolescent transition behaviors (e.g., sexuality, smoking, and drinking) through an interacting adolescent network. A theory of social contagion is defined to explain how social influence affects sexual development. Contacts within a network can, with some transition rate or probability, result in an increase in level of sexual experience. Five stages of sexual development are posited. One submodel proposes a systematic progression through these stages; a competing submodel treats each as an independent process. These models are represented in sets of dynamically interacting recursive equations, which are fit to empirical prevalence data to estimate parameters. Model adjustments are substantively interpretable and can be used to test for and better understand social interaction processes that affect adolescent sexual behavior.

Adolescent↗
PubMed1993

Statistical analysis of neural organization.

1. The responses of 32 taste neurons in the solitary nucleus of the rat to 12 stimuli were analyzed with multidimensional scaling (MDS) and cluster analysis (CA) procedures. These analyses of empirical taste data were compared with similar analyses of two model data sets of known configuration to help clarify the implications of these methods commonly used in forming conclusions about the organization of the taste system. 2. To relate to possible conclusions about groupings in taste, both model data sets were chosen as the best possible examples of ungrouped data, the first being completely regular (in the form of a checkerboard) across the taste space, the second randomly arranged. The analysis of the present empirical data appear to be similar to the present ungrouped models, more so the random than the regular model, in the sense that all are amenable to grouping. 3. Because of the similarity of these model MDS and CA solutions to the present empirical solutions and to most published analyses of this sort, the idea is suggested that the appearance of the plots per se for empirical data does not support the conclusion of grouping. And, technically, MDS and CA do not have the statistical power to provide conclusions about issues of neural organization. 4. MDS and CA analyses have two very powerful roles relating to their ability to disclose the hidden organization of complex data sets; they may lend support for or refute theories about the data sets developed from other considerations, and may help generate theories for further consideration. The question of groupings is only one of many such issues. 5. Because data in the present and other reports are quite adequately accounted by MDS solutions of low dimensionality, it is suggested that their organization is characterized as continuous (i.e., rather than belonging to several disjoint spaces). 6. The use of correlations as distance measures in MDS and CA procedures distorts the spatial solutions, making analysis by visual inspection misleading. For example, using correlations, the true or natural spatial arrangements of data sets are probably less circular or spherical than shown in published MDS solutions. Also they are probably more evenly distributed across the space in the sense that the points are actually more concentrated toward the centers of the spaces; this may have strong influences on interpretations of the general form of the solutions. CA solutions can be influenced in analogous fashion. These problems of distortion of the solutions can be avoided with use of direct, linear estimates of distances. (ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1992

Sibling delinquency and the family environment: shared and unshared influences.

Few family studies of delinquency have focused on siblings. We use a sibling research design to evaluate shared (i.e., family) and unshared environmental influences on delinquency. The 15-22-year-old adolescent siblings were nationally representative, and uniquely, in families of 2 to 4 siblings. No unshared family environmental influences were found for sisters and for mixed-sex siblings, but they may exist for brothers. The data suggested substantial shared environmental and/or shared genetic influences for siblings: the median sibling correlations, averaged over family sizes, were: brothers, r = .30; sisters, r = .28, and mixed sex, r = .21.

Adolescent↗
PubMed1991

Adolescent smoking and drinking: are they "epidemics"?

During adolescence, cumulative prevalences of ever using alcohol and ever smoking a cigarette increase systematically and dramatically. We applied a statistical theory of the transmission of epidemic infectious disease to model life-time prevalences of smoking and drinking. Alcohol use prevalences fit closely to a logistic curve used to model an epidemic process that assumed adolescents have random contacts with one another each year. An "adequate contact" will convert a nondrinker to drinking status if he/she is contacted; drinkers average .48 adequate contacts per year. Smoking prevalences were fit assuming both that the entire population was "at risk" and that some individuals were "immune": the mean contact parameter was .28 for smoking if no immune class was assumed and .77 if an immune class was assumed. Extensions of these epidemic process models could include individual differences in contact rates and transitions among several smoking or drinking statuses (e.g., non-user, experimenter, regular user and recovered user).

Adolescent↗
PubMed1980

Lethal inflammatory pseudotumor masquerading as "laryngitis".

An unusual case of sudden death in a healthy young man due to an inflammatory pseudotumor (polyp) of the larynx is presented. An indirect laryngoscopy performed in the emergency department or accomplishment of a thorough follow-up ear, nose, and throat examination may have been lifesaving in this patient.

Adult↗
PubMed1976

The anion gap: its use in quality control.

Because the anion gap is useful in classifying acid-base disorders, quantitative information on this variable should be readily available. Three populations were studied and means and central 90% ranges were determined for the anion gap, calculated as sodium-(chloride + bicarbonate). In 1047 hospitalized patients the mean was 12 mEq/liter, 86 faster volunteers had a mean of 13 mEq/liter with a 90% range of 9--17 mEq/liter, and 203 plasmaphoresis donors had a mean of 11 mEq/liter with a 90% range of 7--16 mEq/liter. Most of this variability can be accounted for by analytical rather than physiological variation. This quantitation of the anion gap is useful for interchecking electrolyte values as an additional and inexpensive means of laboratory quality control. In 73 of 75 abnormal anion gaps, for which the data were verified to be correct, the clinical information provided a reasonable explanaation for the abnormality.

Acid-Base Imbalance↗
PubMed1975

Pre-instrumental variables in coagulation testing.

A number of variables thought to affect measurement of prothrombin time (PT) and partial thromboplastin time (PTT) were examined in an effort to determine more precisely their effects on these measurements. On the basis of these studies, it is proposed that blood specimens be anticoagulated with one part 3.8% (w./v.) sodium citrate solution to 19 parts whole blood to avoid excessive anticoagulation of blood samples drawn from patients with polycythemia. Because of the smaller amount of plasma in such samples, relatively larger amounts of anticoagulant are used, and spuriously prolonged PT and PTT measurements commonly result. No deleterious effect on anemic specimens is evident when the smaller amount of citrate is used. Studies of the stability of these specimens indicate that unopened, vacuum-drawn specimens do not noticeably deteriorate for as long as 6 hours, even when kept at room temperature. Prothrombin time measurements remain constant for as long as 24 hours. However, a 10--15% lengthening of the partial thromboplastin time is evident after 24 hours of storage.

Anticoagulants↗
PubMedDate not supplied

What causes birth order-intelligence patterns? The admixture hypothesis, revived.

Recent evidence shows that the relation between birth order and intelligence is not the same in cross-sectional and within-family data. This simple empirical observation invalidates the conclusions from hundreds of previous birth order studies that relied on cross-sectional data. Simultaneously, the empirical foundation disappears from underneath theories like dilution and the confluence model that use explanatory processes occurring within the family. A theory proposed almost 25 years ago--the admixture hypothesis--effectively accounts for these empirical patterns. In this article, the author describes why birth order is of such intense interest to both parents and researchers (the birth order trap), discusses past birth order-intelligence patterns, shows that the admixture hypothesis accounts for those patterns, and reframes the original argument to support future productive research efforts.

Birth Order↗