Showing papers on "Population published in 1977"

The CES-D Scale: A Self-Report Depression Scale for Research in the General Population

Abstract: The CES-D scale is a short self-report scale designed to measure depressive symptomatology in the general population. The items of the scale are symptoms associated with depression which have been used in previously validated longer scales. The new scale was tested in household interview surveys and in psychiatric settings. It was found to have very high internal consistency and adequate test- retest repeatability. Validity was established by pat terns of correlations with other self-report measures, by correlations with clinical ratings of depression, and by relationships with other variables which support its construct validity. Reliability, validity, and factor structure were similar across a wide variety of demographic characteristics in the general population samples tested. The scale should be a useful tool for epidemiologic studies of de pression.

Men and Women of the Corporation

Abstract: * Introduction The Players And The Stage * Men and Women of the Corporation: The Population * Industrial Supply Corporation: The Setting Roles And Images * Managers * Secretaries * Wives Structures And Processes * Opportunity * Power * Numbers: Minorities and Majorities Understanding The Action * Contributions to Theory: Structural Determinants of Behavior in Organizations * Contributions to Practice: Organizational Change, Affirmative Action, and the Quality of Work Life * Afterword to the 1993 Edition

An introduction to statistical methods and data analysis

Abstract: PART I: INTRODUCTION 1. WHAT IS STATISTICS? Introduction / Why Study Statistics? / Some Current Applications of Statistics / What Do Statisticians Do? / Quality and Process Improvement / A Note to the Student / Summary / Supplementary Exercises PART II: COLLECTING THE DATA 2. USING SURVEYS AND SCIENTIFIC STUDIES TO COLLECT DATA Introduction / Surveys / Scientific Studies / Observational Studies / Data Management: Preparing Data for Summarization and Analysis / Summary PART III: SUMMARIZING DATA 3. DATA DESCRIPTION Introduction / Describing Data on a Single Variable: Graphical Methods / Describing Data on a Single Variable: Measures of Central Tendency / Describing Data on a Single Variable: Measures of Variability / The Box Plot / Summarizing Data from More Than One Variable / Calculators, Computers, and Software Systems / Summary / Key Formulas / Supplementary Exercises PART IV: TOOLS AND CONCEPTS 4. PROBABILITY AND PROBABILITY DISTRIBUTIONS How Probability Can Be Used in Making Inferences / Finding the Probability of an Event / Basic Event Relations and Probability Laws / Conditional Probability and Independence / Bayes's Formula / Variables: Discrete and Continuous / Probability Distributions for Discrete Random Variables / A Useful Discrete Random Variable: The Binomial / Probability Distributions for Continuous Random Variables / A Useful Continuous Random Variable: The Normal Distribution / Random Sampling / Sampling Distributions / Normal Approximation to the Binomial / Summary / Key Formulas / Supplementary Exercises PART V: ANALYZING DATA: CENTRAL VALUES, VARIANCES, AND PROPORTIONS 5. INFERENCES ON A POPULATION CENTRAL VALUE Introduction and Case Study / Estimation of / Choosing the Sample Size for Estimating / A Statistical Test for / Choosing the Sample Size for Testing / The Level of Significance of a Statistical Test / Inferences about for Normal Population, s Unknown / Inferences about the Population Median / Summary / Key Formulas / Supplementary Exercises 6. COMPARING TWO POPULATION CENTRAL VALUES Introduction and Case Study / Inferences about 1 - 2: Independent Samples / A Nonparametric Alternative: The Wilcoxon Rank Sum Test / Inferences about 1 - 2: Paired Data / A Nonparametric Alternative: The Wilcoxon Signed-Rank Test / Choosing Sample Sizes for Inferences about 1 - 2 / Summary / Key Formulas / Supplementary Exercises 7. INFERENCES ABOUT POPULATION VARIANCES Introduction and Case Study / Estimation and Tests for a Population Variance / Estimation and Tests for Comparing Two Population Variances / Tests for Comparing k > 2 Population Variances / Summary / Key Formulas / Supplementary Exercises 8. INFERENCES ABOUT POPULATION CENTRAL VALUES Introduction and Case Study / A Statistical Test About More Than Two Population Variances / Checking on the Assumptions / Alternative When Assumptions are Violated: Transformations / A Nonparametric Alternative: The Kruskal-Wallis Test / Summary / Key Formulas / Supplementary Exercises 9. MULTIPLE COMPARISONS Introduction and Case Study / Planned Comparisons Among Treatments: Linear Contrasts / Which Error Rate Is Controlled / Multiple Comparisons with the Best Treatment / Comparison of Treatments to a Control / Pairwise Comparison on All Treatments / Summary / Key Formulas / Supplementary Exercises 10. CATEGORICAL DATA Introduction and Case Study / Inferences about a Population Proportion p / Comparing Two Population Proportions p1 - p2 / Probability Distributions for Discrete Random Variables / The Multinomial Experiment and Chi-Square Goodness-of-Fit Test / The Chi-Square Test of Homogeneity of Proportions / The Chi-Square Test of Independence of Two Nominal Level Variables / Fisher's Exact Test, a Permutation Test / Measures of Association / Combining Sets of Contingency Tables / Summary / Key Formulas / Supplementary Exercises PART VI: ANALYZING DATA: REGRESSION METHODS, MODEL BUILDING 11. SIMPLE LINEAR REGRESSION AND CORRELATION Linear Regression and the Method of Least Squares / Transformations to Linearize Data / Correlation / A Look Ahead: Multiple Regression / Summary of Key Formulas. Supplementary Exercises. 12. INFERENCES RELATED TO LINEAR REGRESSION AND CORRELATION Introduction and Case Study / Diagnostics for Detecting Violations of Model Conditions / Inferences about the Intercept and Slope of the Regression Line / Inferences about the Population Mean for a Specified Value of the Explanatory Variable / Predictions and Prediction Intervals / Examining Lack of Fit in the Model / The Inverse Regression Problem (Calibration): Predicting Values for x for a Specified Value of y / Summary / Key Formulas / Supplementary Exercises 13. MULTIPLE REGRESSION AND THE GENERAL LINEAR MODEL Introduction and Case Study / The General Linear Model / Least Squares Estimates of Parameters in the General Linear Model / Inferences about the Parameters in the General Linear Model / Inferences about the Population Mean and Predictions from the General Linear Model / Comparing the Slope of Several Regression Lines / Logistic Regression / Matrix Formulation of the General Linear Model / Summary / Key Formulas / Supplementary Exercises 14. BUILDING REGRESSION MODELS WITH DIAGNOSTICS Introduction and Case Study / Selecting the Variables (Step 1) / Model Formulation (Step 2) / Checking Model Conditions (Step 3) / Summary / Key Formulas / Supplementary Exercises PART VII: ANALYZING DATA: DESIGN OF EXPERIMENTS AND ANOVA 15. DESIGN CONCEPTS FOR EXPERIMENTS AND STUDIES Experiments, Treatments, Experimental Units, Blocking, Randomization, and Measurement Units / How Many Replications? / Studies for Comparing Means versus Studies for Comparing Variances / Summary / Key Formulas / Supplementary Exercises 16. ANALYSIS OF VARIANCE FOR STANDARD DESIGNS Introduction and Case Study / Completely Randomized Design with Single Factor / Randomized Block Design / Latin Square Design / Factorial Experiments in a Completely Randomized Design / The Estimation of Treatment Differences and Planned Comparisons in the Treatment Means / Checking Model Conditions / Alternative Analyses: Transformation and Friedman's Rank-Based Test / Summary / Key Formulas / Supplementary Exercises 17. ANALYSIS OF COVARIANCE Introduction and Case Study / A Completely Randomized Design with One Covariate / The Extrapolation Problem / Multiple Covariates and More Complicated Designs / Summary / Key Formulas / Supplementary Exercises 18. ANALYSIS OF VARIANCE FOR SOME UNBALANCED DESIGNS Introduction and Case Study / A Randomized Block Design with One or More Missing Observations / A Latin Square Design with Missing Data / Incomplete Block Designs / Summary / Key Formulas / Supplementary Exercises 19. ANALYSIS OF VARIANCE FOR SOME FIXED EFFECTS, RANDOM EFFECTS, AND MIXED EFFECTS MODELS Introduction and Case Study / A One-Factor Experiment with Random Treatment Effects / Extensions of Random-Effects Models / A Mixed Model: Experiments with Both Fixed and Random Treatment Effects / Models with Nested Factors / Rules for Obtaining Expected Mean Squares / Summary / Key Formulas / Supplementary Exercises 20. SPLIT-PLOT DESIGNS AND EXPERIMENTS WITH REPEATED MEASURES Introduction and Case Study / Split-Plot Designs / Single-Factor Experiments with Repeated Measures / Two-Factor Experiments with Repeated Measures on One of the Factors / Crossover Design / Summary / Key Formulas / Supplementary Exercises PART VIII: COMMUNICATING AND DOCUMENTING THE RESULTS OF A STUDY OR EXPERIMENT 21. COMMUNICATING AND DOCUMENTING THE RESULTS OF A STUDY OR EXPERIMENT Introduction / The Difficulty of Good Communication / Communication Hurdles: Graphical Distortions / Communication Hurdles: Biased Samples / Communication Hurdles: Sample Size / The Statistical Report / Documentation and Storage of Results / Summary / Supplementary Exercises

Problem Behavior and Psychosocial Development: A Longitudinal Study of Youth

Abstract: This study is the 2nd phase of a long-term program of research on problem behavior. The approach to theory testing involves a longitudinal design. The study plots trajectories of change over time in personality social environment and behavior and uses the theory to forecast important transitions--beginning to drink starting to use marijuana and becoming a nonvirgin. The book has 4 main sections: 1) an introductory chapter and a chapter describing problem-behavior theory and research design and method 2) the cross-sectional findings and their bearing on the theory 3) the longitudinal findings and 4) studies of socialization and conclusions. Using adolescents and youths in American society in the late 1960s and early 1970s this research represents a logical continuation of a long term interest in problem behavior and a recognition that what was going on among youth and in the student movement can be viewed from a problem-behavior perspective. This high school study began in the spring of 1969 with grades 7 8 and 9; by the end of the study in 1972 these participants had all made the transition from junior to senior high school of grades 10 11 and 12. Each year each participant completed a 50 page questionnaire inquiring about their drug use sexual behavior alcohol drinking and the problem behavior associated with excessive use of alcohol. Some of the major findings suggest that: 1) the prevalence of problem behaviors is substantial at the college level and while much lower sizable at the high school level; 2) personal controls appear to be most influential in relation to the set of problem behaviors motivational-instigations are next and personal beliefs are least; 3) the adolescent who is less likely to engage in problem behavior is one who values academic achievement and expects to do well academically; 4) within the distal structure the variables that indicate whether a youth is parent-oriented or peer-oriented are the most significant; and 5) the developmental changes most often measured in connection with growth trends are growth of independence decline in traditional ideology related to achievement value and society as a whole assumption of a more relativistic and tolerant morality attenuation of conventional norms and religious beliefs increase in peer influence and increase in problem behavior itself. Overall it would be an important step forward for prevention and control if problem behavior in youth came to be seen as part of the dialectic of growth.

Conditions controlling the proliferation of haemopoietic stem cells in vitro.

Abstract: A liquid culture system is described whereby proliferation of haemopoietic stem cells (CFU-S), production of granulocyte precursor cells (CFU-C), and extensive granulopoiesis can be maintained in vitro for several months. Such cultures consist of adherent and non-adherent populations of cells. The adherent population contains phagocytic mononuclear cells, “epithelial” cells, and “giant fat” cells. The latter appear to be particularly important for stem cell maintenance and furthermore there is a strong tendency for maturing granulocytes to selectively cluster in and around areas of “giant fat” cell aggregations. By “feeding” the cultures at weekly intervals, between 10 to 15 “population doublings” of functionally normal CFU-S regularly occurs. Increased “population doublings” may be obtained by feeding twice weekly. The cultures show initially extensive granulopoiesis followed, in a majority of cases, by an accumulation of blast cells. Eventually both blast cells and granulocytes decline and the cultures contain predominantly phagocytic mononuclear cells. Culturing at 33°C leads to the development of a more profuse growth of adherent cells and these cultures show better maintenance of stem cells and increased cell density. When tested for colony stimulating activity (CSA) the cultures were uniformly negative. Addition of exogenous CSA caused a rapid decline in stem cells, reduced granulopoiesis and an accumulation of phagocytic mononuclear cells.

Habitat, the template for ecological strategies?

Abstract: The very etymology of Ecology, from the greek 'Qikos', 'the household', implies that ecologists should devote some attention to the 'house' or habitat of the population or community they are studying. However, as Charles Elton (1966) has so forcibly pointed out, 'definition of habitats, or rather lack of it, is one of the chief blind spots in Zoology'. Elton himself has provided us with a qualitative classification of habitats, while another past President, Alex Watt (1947) highlighted the dynamic nature of habitats by his phrase, 'pattern and process'. Elton referred to the need to quantify habitat characteristics. In this Address I will attempt some quantification;however, you will all be aware that in doing this I will not be able to emulate those former Presidents who have been able to provide a definitative synthesis of a field or of their own studies, my offering can be but a small beginning, an indication of the type of characteristics we should quantify. In considering ecosystem patterns and environment R. M. May (1974) writes 'it is to be emphasized that although patterns may underlie the rich and varied tapestry of the natural world, there is no single simple pattern. Theories must be pluralistic'. Indeed, the complexity of the subject is daunting and in any attempt to formulate some type of general framework, one is continually beset with exceptions. In stressing the need for a framework I am echoing a plea of my predecessor Amyan Macfadyen (1975) who cited K. E. F. Watt's (1971) vivid image 'if we do not develop a strong theoretical core that will bring all parts of ecology back together we shall all be washed out to sea in an immense tide of unrelated information'. In some ways I think we may see ourselves at a similar point to the inorganic chemist before the development of the periodic table; then he could not predict, for example, how soluble a particular sulphate would be, or what was the likelihood of a particular reaction occurring. Each fact had to be discovered for itself and each must be remembered in isolation. It is noteworthy that from Dobereiner's early efforts in 1816 it took more than fifty years before Mendeleeff ormulated his Periodic Law (1869) and even after this there were various attempts at rearrangement. Another parallel may be drawn with astronomy before the development of the Hertzsprung-Russell diagram that relates the evolution and the properties of stars. Again in our own subject biology, the situation is somewhat analagous to that before the formulation of the Linnean system of classification; but now from this system of classification, we are able to organize our knowledge of, for example, the functional morphology of organisms and we can even make assumptions, with a high probability

Serial passaging and differentiation of myogenic cells isolated from dystrophic mouse muscle

Abstract: THE muscular dystrophies are a group of hereditary disorders manifested by a progressive wasting of the skeletal muscles. In spite of extensive studies, the nature of the primary lesion is unknown (for review see ref. 1). Because of the complex interaction between tissues, it is difficult to study this question in vivo. Therefore attempts have been made to investigate this question in cultures of dystrophic muscles of human or animal origin. Tissue explants as well as monolayer primary cell cultures contain, in addition to the myogenic cells, a heterogeneous cell population, the composition of which might differ in normal and dystrophic muscle cultures. It is difficult in such experiments to distinguish between properties intrinsic to the myogenic cells and effects exerted by other cell types. Indeed, previous experiments have yielded conflicting conclusions2–6. We therefore tested the possibility of obtaining cell cultures consisting of pure populations of myogenic cells obtained from dystrophic muscles. The present report describes the isolation of a cloned population of such cells, derived from adult dystrophic mouse muscle, that can proliferate and differentiate in cell culture.

An Economic Analysis of Marital Instability

Abstract: This paper focuses on the causes of marital instability. Section I develops a theoretical analysis of marital dissolution, incorporating uncertainty about outcomes of marital decisions into a framework of utility maximization and the marriage market. Section II explores implications of the theoretical analysis with cross-sectional data, primarily the 1967 Survey of Economic Opportunity and the Terman sample. The relevance of both the theoretical and empirical analyses in explaining the recent acceleration in divorce rates is also discussed.

Self-Organization in Nonequilibrium Systems: From Dissipative Structures to Order through Fluctuations

Abstract: Conservation Equations. Thermodynamics of Irreversible Processes: The Linear Region. Nonlinear Thermodynamics. Systems Involving Chemical Reactions and Diffusion-Stability. Mathematical Tools. Simple Autocatalytic Models. Some further Aspects of Dissipative Structures and Self-Organization Phenomena. General Comments. Birth and Death Descriptions of Fluctuations: Nonlinear Master Equation. Self-Organization in Chemical Reactions. Regulatory Processes at the Subcellular Level. Regulatory Processes at the Cellular Level. Cellular Differentiation and Patter Formation. Thermodynamics of Evolution. Thermodynamics of Ecosystems. Perspectives and Concluding Remarks. References. Index.

Metastasis Results from Preexisting Variant Cells Within a Malignant Tumor

Abstract: Clones derived in vitro from a parent culture of murine malignant melanoma cells varied greatly in their ability to produce metastatic colonies in the lungs upon intravenous inoculation into syngeneic mice. This suggests that the parent tumor is heterogeneous and that highly metastatic tumor cell variants preexist in the parental population.

Dispersal in stable habitats

Abstract: Simple mathematical models show that adaptations for achieving dispersal retain great importance even in uniform and predictable environments. A parent organism is expected to try to enter a high fraction of its propagules into competition for sites away from its own immediate locality even when mortality to such dispersing propagules is extremely high. The models incidentally provide a case where the evolutionarily stable dispersal strategy for individuals is suboptimal for the population as a whole.

Pharmacologically induced selective degeneration of chemosensitive primary sensory neurones

Abstract: PHARMACOLOGICALLY evoked selective degeneration of neurones with a specific function or functioning with known transmitter substances, has been reported only in the monoaminergic neurone systems1,2. We report here that selective degeneration of neurones with a highly specific function can be produced by chemical agents in the somatosensory system as well. Capsaicin given to newborn rats induces selective degeneration of a distinct population of primary sensory neurones involved in mediation of chemogenic pain.

Ability of polymorphonuclear leukocytes to orient in gradients of chemotactic factors.

Abstract: Polymorphonuclear leukocyte (PMN) chemotaxis has been examined under conditions which allow phase microscope observations of cells responding to controlled gradients of chemotactic factors. With this visual assay, PMNs can be seen to orient rapidly and reversibly to gradients of N-formylmethionyl peptides. The level of orientation depends upon the mean concentration of peptide present as well as the concentration gradient. The response allows an estimation of the binding constant of the peptide to the cell. In optimal gradients, PMNs can detect a 1% difference in the concentration of peptide. At high cell densities, PMNs incubated with active peptides orient their locomotion away from the center of the cell population. This orientation appears to be due to inactivation of the peptides by the cells. Such inactivation in vivo could help to limit an inflammatory response.

Applied Mathematical Demography

Abstract: Introduction: Population Without Age.- The Life Table.- The Matrix Model Framework.- Mortality Comparisons The Male-Female Ratio.- Fixed Regime of Mortality and Fertility: The Uses of Stable Theory.- Birth and Population Increase from the Life Table.- Birth and Population Increase from Matrix Population Models.- Reproductive Value from the Life Table.- Reproductive Value from Matrix Models.- Understanding Population Characteristics.- Markov Chains for Individual Life Histories.- Projection and Forecasting.- Perturbation Analysis of Matrix Models.- Some Types of Instability.- The Demographic Theory of Kinship.- Microdemography.- The Multi-State Model.- Family Demography.- Heterogeneity and Selection in Population Analysis.- Epilogue: How Do We Know the Facts of Demography?.

Comparison of Stopping Rules in Forward “Stepwise” Regression

Abstract: This paper uses the unconditional mean square error of prediction as a criterion for comparing stopping rules used with the forward “stepwise” selection procedure in multivariate normal samples, based on simulations of 48 population correlation matrices. The CP statistic, “F to enter” (.15 < α < .25), a rule which minimizes the sample criterion, and one which sequentially tests the equality of the population criterion (.25 < α < .35) are superior. For these rules, the criterion seldom differs by more than three percent, although there are considerable differences between these and some of the other rules.

NCHS Growth Curves for Children Birth-18 Years

Abstract: : In 1974 the National Academy of Sciences' urged that new growth charts for infants and children be prepared using current data for the nutritional assessment of populations of infants and children in the United States. The Academy recommended using the data on growth and development collected over the past decade by the Health Examination Surveys (HES) of the National Center for Health Statistics (NCHS), supplemented by age-appropriate sets of height and weight data on infants and children from the Fels Research Institute and from an Ohio State University team headed by Dr. George Owen. Earlier (1971), a study group, cosponsored by the American Academy of Pediatrics and the Maternal and Child Health Program, Public Health Service, Department of Health, Education, and Welfare (DHEW), had made similar recommendations. This latter report emphasized the use of such data in the clinical assessment of the growing infant and child, thereby supplementing nutritional screening and other epidemiologic assessments of populations of children. Again, in 1975, a research-oriented study group sponsored by the National Institute of Child Health and Human Development made similar recommendations . Furthermore, each of the groups recommended that one set of data for all races would be sufficient for practical purposes, despite the small but actual differences in body measurements noted among racial groupings.

Students and Housewives: Differences in Susceptibility to Reference Group Influence

Abstract: Two different samples consisting of housewives and students, respectively, were examined in terms of differences in their susceptibility to reference group influence. The results reveal significant differences between housewives and students in terms of the influence which the three types of reference groups have upon brand selection. The findings raise a serious question concerning the external validity of studies which use students as subjects yet make generalizations to a broader population base.

A Macrosociological Theory of Social Structure

Abstract: Social structure is conceptualized as the distributions of a population among social positions in a multidimensional space of positions. This quantitative conception of social structure is the basis for a deductive theory of the macrostructure of social associations in society. The likelihood that people engage in intergroup associations under specifiable structural conditions can bededuced from analaytic propositions about structural properties without any assumption about sociopsychological dispositions to establish intergroup associations, indeed, on the assumption that people prefer ingroup relations. Group size governs the probability of intergroup relations, a fact that has paradoxical implications for discrimination by a majority against a minority. Inequality impedes and heterogeneity promotes intergroup relations. The major structural condition that governs intergroup relations is the degree of connection of parameters. Intersecting parameters exert structural constraints to participate in interg...

Statistical concepts and methods

Abstract: Introduction. Descriptive Study of Data. Elements of Probability. Random Variables and Probability Distributions. Distributions for Counts. Basic Concepts of Testing Hypotheses. The Normal Distribution and Random Samples. Inferences about a Population. Comparing Two Treatments. Regression Analysis: Simple Linear Relation. Regression Analysis: Model Checking and Multiple Linear Regression. Correlation: A Measure of Linear Relationship. Analysis of Categorized Data. Design of Experiments and Analysis of Variance. Nonparametric Inference. Sample Surveys.

Laminar differences in receptive field properties of cells in cat primary visual cortex

Abstract: 1. Cells in area 17 of the cat visual cortex were studied with a view towards correlating receptive field properties with layering. A number of receptive field parameters were measured for all units, and nearly every unit was marked with a microlesion to determine accurately the layer in which it was found. 2. Cells were defined as simple or complex by mapping with stationary stimuli, using the criteria of Hubel & Wiesel (1962). Complex cells fell into two groups: those that showed summation for increased slit length (standard complex) and those that did not (special complex). 3. The simple cells were located in the deep part of layer 3, in layer 4, and in layer 6. This corresponds to the distribution of afferents from the dorsal layers of the lateral geniculate nucleus. In these cortical layers the simple cells differed primarily with respect to their receptive field size, cells in layer 4 having the smallest, layer 3 intermediate, and layer 6 the largest fields. Layer 4 was the only layer in which simple cells showed end-inhibition (a reduction in response to slits extending beyond the excitatory portion of the receptive field). 4. The standard complex cells were found in all layers, but were quite scarce in layer 4. As with the simple cells, field size varied with layer: in layer 2+3 they had small to intermediate field sizes, in layer 5 intermediate, and in layer 6 very large. Layer 6 cells showed summation for slits of increased length up to very large values, and responded best when the slits were centred in the receptive field. The only standard complex cells that showed end-inhibition were those in layer 2+3, and these were similar to the layer 4 simple cells in terms of proportion of end-inhibited units and degree of end-inhibition. 5. The special complex cells, originally described by Palmer & Rosenquist (1974), were found in two tiers: the upper one at the layer 3/layer 4 border and the lower one in layer 5. They were different from the standard complex cells in having a high spontaneous activity, high velocity preference, and large fields which were similar in size (at a given eccentricity) from one cell to the next. Many showed reduced response to slits of increasing length, even for slits that did not extend beyond the borders of the responsive region. 6. Cells in layer 6 (the origin of the corticogeniculate projection) were antidromically activated from the lateral geniculate nucleus. The antidromically activated units included both simple and complex cells, and they had the long receptive fields characteristic of the overall population of cells in layer 6. 7. The results showed that there are different types of simple and complex cells, and that cells in different layers have different properties. Taken together with their differences in site of projection, this demonstrates that the anatomical lamination pattern is reflected in functional differences between cells in different layers.

A new pathway for DNA repair in Escherichia coli.

Abstract: MOST studies on mutagenesis involve exposing a growing population of cells to a large dose of mutagen for a short period. In a natural environment, however, cells are probably exposed more often to a low concentration of mutagens for long periods. We therefore measured the accumulation of mutants in Escherichia coli cells growing continuously in the presence of very low concentrations of mutagens. Because many mutagens are highly unstable, it was necessary to devise a system in which cells could be continuously exposed to fresh mutagen. To do this we took advantage of the fact that certain bacteria can grow and divide while attached to the underside of a Millipore filter. This system was originally developed by Helmstetter and Cummings1 as a means of producing synchronous cells, because as growth medium is passed through the filter it carries away with it the unattached daughter from each pair of newly divided cells. The mutagen to be studied can therefore be stored in stable conditions and only mixed with the growth medium immediately before being passed through the filter; for example the mutagen N-methyl-N′-nitro-nitro-soguanidine (MNNG) can be stored in citrate buffer at pH 5.0 in which it has a half life of 40 h compared with 2.3 h in synthetic minimal media2,3. We had intended to determine the relationship between ambient concentration of various mutagens and resulting mutation rate. The first mutagen studied was MNNG and the results were totally unexpected.

When is sex environmentally determined

Abstract: THERE are several sex determining mechanisms which produce two sexes in a population (dioecy or gonochorism)1–5. In many of these, the offspring's sex is determined at or before conception, as in male or female heterogamety. In several organisms, however, the offspring's sex is determined later than conception, by some environmental influence upon the offspring. We consider here why these environmental mechanisms have been maintained; that is, why have they not been replaced with an alternative system that determines sex at conception? We propose that labile sex determination (not fixed at conception) is favoured by natural selection when an individual's fitness (as a male or female) is strongly influenced by environmental conditions and where the individual has little control over which environment it will experience. Our argument also applies to sex expression in hermaphrodites6,7.

Estimation of population characteristics of pharmacokinetic parameters from routine clinical data

Abstract: A general data analysis technique estimates average population values of pharmacokinetic parameters and their interindividual variability from clinical pharmacokinetic data gathered during the routine care of patients. Several drug concentration values from each individual, along with dosage information and the values of other routinely assessed variables suffice for purposes of analysis. The Maximum Likelihood principle estimates underlying population values without the necessity for the intermediate estimation of individual parameter values. The approach is quite general, permitting the use of nonlinear statistical models with both fixed and random effects. Complex expressions involving physiological variables can be used to define the pharmacokinetic parameters. Thus, the relationship of physiological factors to parameter values can be assessed. The generality and appropriateness of the analysis technique are demonstrated by analysis of a set of data derived from 141 patients receiving the drug digoxin.

Association of Cancer Sites With Tobacco and Alcohol Consumption and Socioeconomic Status of Patients: Interview Study From the Third National Cancer Survey

Abstract: From personal interviews obtained for 7,518 incident cases of invasive cancer from the population-based Third National Cancer Survey, the quantitative lifetime use of cigarettes, cigars, pipes, unsmoked tobacco, wine, beer, hard liquor, and combined alcohol were recorded, as well as education and family income level. In an initial screening analysis of these data, Mantel-Haenszel 2 X 2 contingency tabulations and multiple regression analyses were used to compare each specific cancer site with controls from other sites to test for associations with the "exposure variables." Significant positive associations with cigarette smoking were found for cancers of the lung, larynx, oral cavity, esophagus, stomach, pancreas, bladder, kidney, and uterine cervix. Other forms of tobacco were associated with cancers of the oral cavity, larynx, lung, and cervix. Consumption of wine, beer, hard liquor, and all combined showed positive associations with neoplasms of the oral cavity larynx, esophagus, colon, rectum, breast, and thyroid gland. College educaton and high income both showed positive associations with cancers of the breast, thyroid gland, uterine corpus, and melanomas in males. These same indicators of high socioeconomic status showed inverse associations with invasive neoplasms of the uterine cervix, lung, lip-tongue, and colon in females. College attendance (but not income) showed an inverse association with stomach cancer and positive association with pancreatic cancer in males. Still other tumor sties showed "suggestive" associations with each of these exposure variables. In the analyses producing these results, age, race, sex, smoking, drinking, education, income, parity, foreign birth, marital status, and geographic location were used as stratification variables separately or in combination when appropriate to assess and control for their potentially confounding affects and to examine results in different strata to assess interaction.

Induction of DNA synthesis in BALB/c 3T3 cells by serum components: Reevaluation of the commitment process

Abstract: Serum contains a growth factor derived from platelets and also growth factors derived from platelet-poor plasma. Extracts of heated (100°) human platelets function synergistically with platelet-poor plasma to induce DNA synthesis in quiescent, density-inhibited BALB/c 3T3 cells. Platelet-poor plasma alone did not induce DNA synthesis. Cells exposed to platelet extracts became competent to enter the cell cycle, but the rate of entry into the S phase depended upon the concentration of platelet-poor plasma. The time required for the induction of this competent state was a function of the concentration of the platelet extract. A 2-hr exposure to 100 μg of the platelet extract at 37° caused the entire cell population to become competent to enter the S phase. At 4° or 25° the cells did not become competent to synthesize DNA. The platelet extract-induced competent state was stable for at least 13 hr after removal of the platelet extract; however, in the absence of platelet-poor plasma, these competent cells did not progress through the cell cycle. The addition of an optimal concentration of platelet-poor plasma (5%) to these competent cells initiated cell cycle traverse with a rapid, first-order entry of cells into the S phase beginning 12 hr after addition of the plasma. The addition of a suboptimal concentration of the plasma (0.25%) did not increase the rate of cell entry into the S phase. Thus, the induction of DNA synthesis in quiescent BALB/c 3T3 cells can be resolved into at least two phases, controlled by different serum components: (i) competence, induced by the platelet-derived growth factor; and (ii) progression of competent cells into the cell cycle, mediated by factors in platelet-poor plasma.