Showing papers on "Population published in 1992"

Analysis of molecular variance inferred from metric distances among DNA haplotypes: application to human mitochondrial DNA restriction data.

Abstract: We present here a framework for the study of molecular variation within a single species. Information on DNA haplotype divergence is incorporated into an analysis of variance format, derived from a matrix of squared-distances among all pairs of haplotypes. This analysis of molecular variance (AMOVA) produces estimates of variance components and F-statistic analogs, designated here as phi-statistics, reflecting the correlation of haplotypic diversity at different levels of hierarchical subdivision. The method is flexible enough to accommodate several alternative input matrices, corresponding to different types of molecular data, as well as different types of evolutionary assumptions, without modifying the basic structure of the analysis. The significance of the variance components and phi-statistics is tested using a permutational approach, eliminating the normality assumption that is conventional for analysis of variance but inappropriate for molecular data. Application of AMOVA to human mitochondrial DNA haplotype data shows that population subdivisions are better resolved when some measure of molecular differences among haplotypes is introduced into the analysis. At the intraspecific level, however, the additional information provided by knowing the exact phylogenetic relations among haplotypes or by a nonlinear translation of restriction-site change into nucleotide diversity does not significantly modify the inferred population genetic structure. Monte Carlo studies show that site sampling does not fundamentally affect the significance of the molecular variance components. The AMOVA treatment is easily extended in several different directions and it constitutes a coherent and flexible framework for the statistical analysis of molecular data.

Risk and protective factors for alcohol and other drug problems in adolescence and early adulthood: Implications for substance abuse prevention.

Abstract: The authors suggest that the most promising route to effective strategies for the prevention of adolescent alcohol and other drug problems is through a risk-focused approach. This approach requires the identification of risk factors for drug abuse, identification of methods by which risk factors have been effectively addressed, and application of these methods to appropriate high-risk and general population samples in controlled studies. The authors review risk and protective factors for drug abuse, assess a number of approaches for drug abuse prevention potential with high-risk groups, and make recommendations for research and practice.

Performing the exact test of Hardy-Weinberg proportion for multiple alleles.

Abstract: SUMMARY The Hardy-Weinberg law plays an important role in the field of population genetics and often serves as a basis for genetic inference. Because of its importance, much attention has been devoted to tests of Hardy-Weinberg proportions (HWP) over the decades. It has long been recognized that largesample goodness-of-fit tests can sometimes lead to spurious results when the sample size and/or some genotypic frequencies are small. Although a complete enumeration algorithm for the exact test has been proposed, it is not of practical use for loci with more than a few alleles due to the amount of computation required. We propose two algorithms to estimate the significance level for a test of HWP. The algorithms are easily applicable to loci with multiple alleles. Both are remarkably simple and computationally fast. Relative efficiency and merits of the two algorithms are compared. Guidelines regarding their usage are given. Numerical examples are given to illustrate the practicality of the algorithms.

Population growth makes waves in the distribution of pairwise genetic differences.

Abstract: Episodes of population growth and decline leave characteristic signatures in the distribution of nucleotide (or restriction) site differences between pairs of individuals. These signatures appear in histograms showing the relative frequencies of pairs of individuals who differ by i sites, where i = 0, 1, .... In this distribution an episode of growth generates a wave that travels to the right, traversing 1 unit of the horizontal axis in each 1/2u generations, where u is the mutation rate. The smaller the initial population, the steeper will be the leading face of the wave. The larger the increase in population size, the smaller will be the distribution's vertical intercept. The implications of continued exponential growth are indistinguishable from those of a sudden burst of population growth Bottlenecks in population size also generate waves similar to those produced by a sudden expansion, but with elevated uppertail probabilities. Reductions in population size initially generate L-shaped distributions with high probability of identity, but these converge rapidly to a new equilibrium. In equilibrium populations the theoretical curves are free of waves. However, computer simulations of such populations generate empirical distributions with many peaks and little resemblance to the theory. On the other hand, agreement is better in the transient (nonequilibrium) case, where simulated empirical distributions typically exhibit waves very similar to those predicted by theory. Thus, waves in empirical distributions may be rich in information about the history of population dynamics.

Validating the SF-36 health survey questionnaire: new outcome measure for primary care.

Abstract: OBJECTIVES--To test the acceptability, validity, and reliability of the short form 36 health survey questionnaire (SF-36) and to compare it with the Nottingham health profile. DESIGN--Postal survey using a questionnaire booklet together with a letter from the general practitioner. Non-respondents received two reminders at two week intervals. The SF-36 questionnaire was retested on a subsample of respondents two weeks after the first mailing. SETTING--Two general practices in Sheffield. PATIENTS--1980 patients aged 16-74 years randomly selected from the two practice lists. MAIN OUTCOME MEASURES--Scores for each health dimension on the SF-36 questionnaire and the Nottingham health profile. Response to questions on recent use of health services and sociodemographic characteristics. RESULTS--The response rate for the SF-36 questionnaire was high (83%) and the rate of completion for each dimension was over 95%. Considerable evidence was found for the reliability of the SF-36 (Cronbach9s alpha greater than 0.85, reliability coefficient greater than 0.75 for all dimensions except social functioning) and for construct validity in terms of distinguishing between groups with expected health differences. The SF-36 was able to detect low levels of ill health in patients who had scored 0 (good health) on the Nottingham health profile. CONCLUSIONS--The SF-36 is a promising new instrument for measuring health perception in a general population. It is easy to use, acceptable to patients, and fulfils stringent criteria of reliability and validity. Its use in other contexts and with different disease groups requires further research.

Fruit, vegetables, and cancer prevention: A review of the epidemiological evidence

Abstract: Approximately 200 studies that examined the relationship between fruit and vegetable intake and cancers of the lung, colon, breast, cervix, esophagus, oral cavity, stomach, bladder, pancreas, and ovary are reviewed. A statistically significant protective effect of fruit and vegetable consumption was found in 128 of 156 dietary studies in which results were expressed in terms of relative risk. For most cancer sites, persons with low fruit and vegetable intake (at least the lower one-fourth of the population) experience about twice the risk of cancer compared with those with high intake, even after control for potentially confounding factors. For lung cancer, significant protection was found in 24 of 25 studies after control for smoking in most instances. Fruits, in particular, were significantly protective in cancers of the esophagus, oral cavity, and larynx, for which 28 of 29 studies were significant. Strong evidence of a protective effect of fruit and vegetable consumption was seen in cancers of the pancreas and stomach (26 of 30 studies), as well as in colorectal and bladder cancers (23 of 38 studies). For cancers of the cervix, ovary, and endometrium, a significant protective effect was shown in 11 of 13 studies, and for breast cancer a protective effect was found to be strong and consistent in a meta analysis. It would appear that major public health benefits could be achieved by substantially increasing consumption of these foods.

Overcoming the Odds: High Risk Children from Birth to Adulthood.

Abstract: This study was a follow-up study of a 1955 cohort of births (614 births) on Kauai island in Hawaii. Follow-up was conducted at birth age one and two years age 10 years age 18 years and 31-32 years. The final sample in adulthood was 505 persons. The sample population was comprised of three ethnic groups (Japanese Filipino and part and full Hawaiian) and 54% grew up in poverty. Births were scored for complications as mild moderate or severe. The interviews conducted with mothers postpartum and at one and two years focused on maternal educational level socioeconomic status and family stability; environmental setting was evaluated as favorable to unfavorable on a five-point scale. The 10 year evaluation assessed school work and school behavioral problems mental abilities and stressful life events and illnesses occurring over the preceding 8 years. The home environment was evaluated on the level of educational stimulation emotional support and socioeconomic status. At 18 years a psychological inventory of self-assurance and interpersonal adequacy was conducted and community records were checked for serious mental health or criminal problems. Quality of life of the home environment was also assessed. The follow-up at age 31-32 years assessed the quality of adult adaptation from community records and interview questions which were self-evaluations of personal success satisfaction with family and social life and psychological well-being. Most of the sample led ordinary lives. Some of the stressful life events in childhood and adolescence were associated with coping problems in adulthood.

Predominant TH2-like bronchoalveolar T-lymphocyte population in atopic asthma

Abstract: Background. In atopic asthma, activated T helper lymphocytes are present in bronchial-biopsy specimens and bronchoalveolar-lavage (BAL) fluid, and their production of cytokines may be important in the pathogenesis of this disorder. Different patterns of cytokine release are characteristic of certain subgroups of T helper cells, termed TH1 and TH2, the former mediating delayed-type hypersensitivity and the latter mediating IgE synthesis and eosinophilia. The pattern of cytokine production in atopic asthma is unknown. Methods. We assessed cells obtained by BAL in subjects with mild atopic asthma and in normal control subjects for the expression of messenger RNA (mRNA) for interleukin-2, 3, 4, and 5, granulocytemacrophage colony-stimulating factor (GM-CSF), and interferon gamma by in situ hybridization with 32P-labeled complementary RNA. Localization of mRNA to BAL T cells was assessed by simultaneous in situ hybridization and immunofluorescence and by in situ hybridization after immunomagnetic enrichment or...

Grading the severity of chronic pain.

Abstract: This research develops and evaluates a simple method of grading the severity of chronic pain for use in general population surveys and studies of primary care pain patients Measures of pain intensity, disability, persistence and recency of onset were tested for their ability to grade chronic pain severity in a longitudinal study of primary care back pain (n = 1213), headache (n = 779) and temporomandibular disorder pain (n = 397) patients A Guttman scale analysis showed that pain intensity and disability measures formed a reliable hierarchical scale Pain intensity measures appeared to scale the lower range of global severity while disability measures appeared to scale the upper range of global severity Recency of onset and days in pain in the prior 6 months did not scale with pain intensity or disability Using simple scoring rules, pain severity was graded into 4 hierarchical classes: Grade I, low disability--low intensity; Grade II, low disability--high intensity; Grade III, high disability--moderately limiting; and Grade IV, high disability--severely limiting For each pain site, Chronic Pain Grade measured at baseline showed a highly statistically significant and monotonically increasing relationship with unemployment rate, pain-related functional limitations, depression, fair to poor self-rated health, frequent use of opioid analgesics, and frequent pain-related doctor visits both at baseline and at 1-year follow-up Days in Pain was related to these variables, but not as strongly as Chronic Pain Grade Recent onset cases (first onset within the prior 3 months) did not show differences in psychological and behavioral dysfunction when compared to persons with less recent onset Using longitudinal data from a population-based study (n = 803), Chronic Pain Grade at baseline predicted the presence of pain in the prior 2 weeks Chronic Pain Grade and pain-related functional limitations at 3-year follow-up Grading chronic pain as a function of pain intensity and pain-related disability may be useful when a brief ordinal measure of global pain severity is required Pain persistence, measured by days in pain in a fixed time period, provides useful additional information

Changing AIDS-risk behavior.

Abstract: This article contains a comprehensive, critical review of the acquired immunodeficiency syndrome (AIDS)-risk-reduction literature on interventions that have targeted risky sexual behavior and intravenous drug use practices. A conceptually based, highly generalizable model for promoting and evaluating AIDS-risk behavior change in any population of interest is then proposed. The model holds that AIDS-risk reduction is a function of people's information about AIDS transmission and prevention, their motivation to reduce AIDS risk, and their behavioral skills for performing the specific acts involved in risk reduction. Supportive tests of this model, using structural equation modeling techniques, are then reported for populations of university students and gay male affinity group members.

A simple regression method for mapping quantitative trait loci in line crosses using flanking markers.

Abstract: The use of flanking marker methods has proved to be a powerful tool for the mapping of quantitative trait loci (QTL) in the segregating generations derived from crosses between inbred lines. Methods to analyse these data, based on maximum-likelihood, have been developed and provide good estimates of QTL effects in some situations. Maximum-likelihood methods are, however, relatively complex and can be computationally slow. In this paper we develop methods for mapping QTL based on multiple regression which can be applied using any general statistical package. We use the example of mapping in an F(2) population and show that these regression methods produce very similar results to those obtained using maximum likelihood. The relative simplicity of the regression methods means that models with more than a single QTL can be explored and we give examples of two lined loci and of two interacting loci. Other models, for example with more than two QTL, with environmental fixed effects, with between family variance or for threshold traits, could be fitted in a similar way. The ease, speed of application and generality of regression methods for flanking marker analysis, and the good estimates they obtain, suggest that they should provide the method of choice for the analysis of QTL mapping data from inbred line crosses.

Stability and Oscillations in Delay Differential Equations of Population Dynamics

Abstract: 1. The Delay Logistic Equation. 2. Delay Induced Bifurcation to Periodicity. 3. Methods of Linear Analysis. 4. Global Attractivity. 5. Models of Neutral Differential Systems. References. Index.

Current Estimates from the National Health Interview Survey, 1991

Abstract: This report on the 1988 civilian noninstitutionalized population residing in the US presents estimates of acute conditions episodes of persons injured restriction in activity limitation of activity due to chronic conditions prevalence of chronic conditions respondent-assessed health status and the use of medical services including physician contacts and short-stay hospitalization. Estimates of these health characteristics are presented in detailed tables for various groups in the population including those defined by age sex race and family income and by geographic regions and place of residence. Accompanying text briefly defines each of the health characteristics included in the detailed tables and reports the 1988 estimate for each characteristic. Text tables include the corresponding 1986 and 1987 estimates for each of the major health characteristics. Information in this report comes from the National Health Interview Survey based on data collected in a continuing nationwide survey by household interview. The 1988 survey was conducted with a full sample including 47485 households containing 122310 persons.

Modeling and forecasting U. S. mortality

Abstract: Time series methods are used to make long-run forecasts, with confidence intervals, of age-specific mortality in the United States from 1990 to 2065. First, the logs of the age-specific death rates are modeled as a linear function of an unobserved period-specific intensity index, with parameters depending on age. This model is fit to the matrix of U.S. death rates, 1933 to 1987, using the singular value decomposition (SVD) method; it accounts for almost all the variance over time in age-specific death rates as a group. Whereas e 0 has risen at a decreasing rate over the century and has decreasing variability, k(t) declines at a roughly constant rate and has roughly constant variability, facilitating forecasting. k(t), which indexes the intensity of mortality, is next modeled as a time series (specifically, a random walk with drift) and forecast. The method performs very well on within-sample forecasts, and the forecasts are insensitive to reductions in the length of the base period from 90 to 30 ...

The strategy of preventive medicine

Abstract: Part 1 The Objectives of Preventive Medicine: The scope for prevention. Why seek to prevent?: the economic and humanitarian arguments. Priorities: a matter of choice Part 2 What needs to be prevented?: Sick individuals: a continuum of disease severity case definitions. A continuum of risk: the prevention paradox mass and individual measures. A unified approach Part 3 The Relation of Risk to Exposure: The dose-effect relationship. The limitations of research methods. Small but widespread risks: a public health disaster? Part 4 Prevention for Individuals and the "High-risk" Strategy Prevention and clinical care The high-risk strategy. Identifying risk-screening. Strengths and weaknesses of the high-risk strategy Part 5 Individuals and Populations: Individual variation: genetic, social and behavioural determinants of diversity. Variation between populations. Sick and healthy populations Part 6 Some Implications of Population change: Effects of the population average on the occurrence of deviance examples from mental health. Health implications for the population as a whole: cardiovascular disease body weight birth weight early development and adult health Down's Syndrome alcohol osteoporosis and fractures occupational and environmental health other fields of application. Safety Part 7 The Population Strategy of Prevention: Principles: the sociological, moral and medical arguments scope proximal and underlying causes. Strengths. Limitations and problems 8. In Search of Health: How do populations change?: the alcohol example. Scientific justification for change. Social engineering versus individual freedom. Freedom of choice. Role of governments. Who takes the decisions? The largest threat to public health: war. Social and economic deprivation. Responsibility for health.

Ecological Processes That Affect Populations in Complex Landscapes

Abstract: We describe a general framework for understanding the ecological processes that operate at landscape scales. The composition of habitat types in a landscape and the physiognomic or spatial arrangement of those habitats are the two essential features that are required to describe any landscape. As such, these two features affect four basic ecological processes that can influence population dynamics or community structure. The first two of these processes, landscape complementation and landscape supplementation, occur when individuals move between patches in the landscape to make use of nonsubstitutable and substitutable resources, respectively

Outward-Oriented Developing Economies Really Do Grow More Rapidly: Evidence from 95 LDCs, 1976-1985

Abstract: The long run trade orientation of an economy is measured in this article by an index which measures the extent to which the real exchange rate is distorted away from its free trade level by the trade regime The technique for estimating a cross country index of real exchange rate distortion uses the international comparison of prices prepared by Robert Summers and Alan Heston Resource endowment constitutes the norm and real overvaluation or undervaluation relative to this norm reveals whether incentives are directed to the domestic or international market The index is constructed based on data for GDP/capita average price level in US dollars 1976-85 and GDP growth rate/capita 1976-85 Other sections are devoted the comparison of the procedure for 117 countries between 1976-85 and an examination of the empirical relationship between outward orientation and economic growth and sensitivity analysis The results indicate that Latin America generally was overvalued by 33% relative to Asia and Africa was overvalued by 86% The real exchange rate distortion index supports the view that Asian countries are more outward oriented Asian economies have lower price levels which reflect relatively modest protection and incentives oriented to external markets Latin American countries with moderately high price level and African countries with very high price levels reflect strong protection and incentives directed to production for the domestic market An alternative specification which eliminates the dummy variables for Africa yields similar results with slightly lower magnitude; ie overvaluation is 60% instead of 86% for Africa and Latin America is overvalued by 39% instead of 33% over Asia A table is provided which indicates by country the distortion and variability of the real exchange rate the GDP growth the 1976 GDP/capita and the investment rate Another finding was that there is a significant negative relationship between distortion of the real exchange rate and growth of GDP/capita after controlling for the effects of real exchange rate variability and investment level with both the original specification and the alternative The growth rate/capita of Latin American and African countries would increase 15-21% with a shift to move outward oriented trade policies This gain as well as devaluation of the real exchange reate trade liberalization and maintenance of a stable real exchange rate would contribute to positive growth rates In the analysis of the poorest 24 countries the result was that only rate distortion and not variability and investment rate explained the growth rate The gain for Ghana for example of adopting the trade policies and exchange rate of Bangladesh would be 5% to its growth

Overcoming the absence of socioeconomic data in medical records: validation and application of a census-based methodology

Abstract: BACKGROUND. Most US medical records lack socioeconomic data, hindering studies of social gradients in health and ascertainment of whether study samples are representative of the general population. This study assessed the validity of a census-based approach in addressing these problems. METHODS. Socioeconomic data from 1980 census tracts and block groups were matched to the 1985 membership records of a large prepaid health plan (n = 1.9 million), with the link provided by each individual's residential address. Among a subset of 14,420 Black and White members, comparisons were made of the association of individual, census tract, and census block-group socioeconomic measures with hypertension, height, smoking, and reproductive history. RESULTS. Census-level and individual-level socioeconomic measures were similarly associated with the selected health outcomes. Census data permitted assessing response bias due to missing individual-level socioeconomic data and also contextual effects involving the interactio...

Incidence, Severity, Aetiology and Prevention of Sports Injuries A Review of Concepts

Abstract: Notwithstanding the healthy influence of sporting activities on risk factors, in particular those of cardiovascular disease, it is becoming increasingly apparent that sports can present a danger to health in the form of sports injuries. The extent of the sports injury problem calls for preventative action based on the results of epidemiological research. For the interpretation of these facts uniform definitions are needed and limitations of research designs should be known. Measures to prevent sports injuries form part of what is called the 'sequence of prevention'. Firstly the extent of the sports injury problem must be identified and described. Secondly the factors and mechanisms which play a part in the occurrence of sports injuries have to be identified. The third step is to introduce measures that are likely to reduce the future risk and/or severity of sports injuries. This measure should be based on the aetiological factors and the mechanism as identified in the second step. Finally the effect of the measures must be evaluated by repeating the first step. In this review some aspects of the first and second step of the sequence of prevention are discussed. The extent of the sports injury problem is often described by injury incidence and by indicators of the severity of sports injuries. Sports injury incidence should preferably be expressed as the number of sports injuries per exposure time (e.g. per 1000 hours of sports participation) in order to facilitate the comparability of research results. However, one should realise that the outcome of research applying this definition of sports injury incidence is highly dependent on the definitions of 'sports injury' and 'sports participation'. The outcome of such research also depends on the applied research design and research methodology. The incidence of sports injuries depends on: the method used to count injuries (e.g. prospective vs retrospective); the method used to establish the population at risk; and on the representativeness of the sample. Severity of sports injuries can be described on the basis of 6 criteria: the nature of the sports injury; the duration and nature of treatment; sporting time lost; working time lost; permanent damage; and cost. Here also uniform definitions are important and necessary in order to enhance the comparability of research data. In the second step of the 'sequence of prevention' the aetiological factors that play a role in the occurrence of a sports injury have to be identified by epidemiological studies. Epidemiological research on the aetiology of sports injuries requires a conceptual model.(ABSTRACT TRUNCATED AT 400 WORDS)

Prevalence of migraine headache in the United States. Relation to age, income, race, and other sociodemographic factors.

Abstract: Objective. —To describe the magnitude and distribution of the public health problem posed by migraine in the United States by examining migraine prevalence, attack frequency, and attack-related disability by gender, age, race, household income, geographic region, and urban vs rural residence. Design. —In 1989, a self-administered questionnaire was sent to a sample of 15000 households. A designated member of each household initially responded to the questionnaire. Each household member with severe headache was asked to respond to detailed questions about symptoms, frequency, and severity of headaches. Setting. —A sample of households selected from a panel to be representative of the US population in terms of age, gender, household size, and geographic area. Participants. —After a single mailing, 20468 subjects (63.4% response rate) between 12 and 80 years of age responded to the survey. Respondents and non-respondents did not differ by gender, household income, region of the country, or urban vs rural status. Whites and the elderly were more likely to respond. Migraine headache cases were identified on the basis of reported symptoms using established diagnostic criteria. Results. —17.6% of females and 5.7% of males were found to have one or more migraine headaches per year. The prevalence of migraine varied considerably by age and was highest in both men and women between the ages of 35 to 45 years. Migraine prevalence was strongly associated with household income; prevalence in the lowest income group ( Conclusions. —A projection to the US population suggests that 8.7 million females and 2.6 million males suffer from migraine headache with moderate to severe disability. Of these, 3.4 million females and 1.1 million males experience one or more attacks per month. Females between ages 30 to 49 years from lower-income households are at especially high risk of having migraines and are more likely than other groups to use emergency care services for their acute condition. (JAMA. 1992;267:64-69)

Calibration Estimators in Survey Sampling

Abstract: This article investigates estimation of finite population totals in the presence of univariate or multivariate auxiliary information. Estimation is equivalent to attaching weights to the survey data. We focus attention on the several weighting systems that can be associated with a given amount of auxiliary information and derive a weighting system with the aid of a distance measure and a set of calibration equations. We briefly mention an application to the case in which the information consists of known marginal counts in a two- or multi-way table, known as generalized raking. The general regression estimator (GREG) was conceived with multivariate auxiliary information in mind. Ordinarily, this estimator is justified by a regression relationship between the study variable y and the auxiliary vector x. But we note that the GREG can be derived by a different route by focusing instead on the weights. The ordinary sampling weights of the kth observation is 1/πk , where πk is the inclusion probabilit...

A comparison of two approaches for identifying reinforcers for persons with severe and profound disabilities

Abstract: The development of effective training programs for persons with profound mental retardation remains one of the greatest challenges for behavior analysts working in the field of developmental disabilities. One significant advancement for this population has been the reinforcer assessment procedure developed by Pace, Ivancic, Edwards, Iwata, and Page (1985), which involves repeatedly presenting a variety of stimuli to the client and then measuring approach behaviors to differentiate preferred from nonpreferred stimuli. One potential limitation of this procedure is that some clients consistently approach most or all of the stimuli on each presentation, making it difficult to differentiate among these stimuli. In this study, we used a concurrent operants paradigm to compare the Pace et al. (1985) procedure with a modified procedure wherein clients were presented with two stimuli simultaneously and were given access only to the first stimulus approached. The results revealed that this forced-choice stimulus preference assessment resulted in greater differentiation among stimuli and better predicted which stimuli would result in higher levels of responding when presented contingently in a concurrent operants paradigm.

Model modifications in covariance structure analysis: the problem of capitalization on chance.

Abstract: In applications of covariance structure modeling in which an initial model does not fit sample data well, it has become common practice to modify that model to improve its fit. Because this process is data driven, it is inherently susceptible to capitalization on chance characteristics of the data, thus raising the question of whether model modifications generalize to other samples or to the population. This issue is discussed in detail and is explored empirically through sampling studies using 2 large sets of data. Results demonstrate that over repeated samples, model modifications may be very inconsistent and cross-validation results may behave erratically. These findings lead to skepticism about generalizability of models resulting from data-driven modifications of an initial model. The use of alternative a priori models is recommended as a preferred strategy.