SEARCH · PubMed Health

Results for “longitudinal data”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources

PubMedDate not supplied

Self-efficacy impacts self-care and HbA1c in young adults with Type I diabetes.

OBJECTIVE: The present study examined self-efficacy and self-esteem as basic aspects of the self that influence self-care and physiological outcomes among young adults with Type I diabetes. The two aims of this study were 1) to examine the cross-sectional and longitudinal role of the self-variables as they predict self-care and HbA1c and 2) to test whether self-care mediates the association between the self variables and HbA1c using cross-sectional and longitudinal data. METHODS: One hundred ten participants were recruited from a regional diabetes outpatient clinic. Inclusion criteria were age (18-35 years) and duration of diabetes (>1 year before recruitment). Participants were 61% female and 88% white. In addition, the sample had an average annual income between $24,999 and $34,999, and 85% had completed some or all of college. The average duration of diabetes was 15 years. RESULTS: Using multiple regression analyses we found that, compared with self-esteem, self-efficacy was a better predictor of all aspects of self-care and HbA1c in cross-sectional analyses, in addition to diet and exercise self-care, and a better predictor of HbA1c in longitudinal analyses. The data also supported the cross-sectional and longitudinal mediational model in which better self-care helped account for the association between greater self-efficacy and better HbA1c. CONCLUSIONS: Self-efficacy is an important factor for management of self-care practices and physiological outcomes among young adults with Type I diabetes, and self-care may be an important mechanism by which self-efficacy influences HbA1c levels.

Adolescent↗

PubMed1996

Simultaneously modelling censored survival data and repeatedly measured covariates: a Gibbs sampling approach.

Recent methodologic developments in the analysis of longitudinal data have typically addressed one of two aspects: (i) the modelling of repeated measurements of a covariate as a function of time or other covariates, or (ii) the modelling of the effect of a covariate on disease risk. In this paper, we address both of these issues in a single analysis by modelling a continuous covariate over time and simultaneously relating the covariate to disease risk. We use the Markov chain Monte Carlo technique of Gibbs sampling to estimate the joint posterior distribution of the unknown parameters of the model. Simulation studies showed that jointly modelling survival and covariate data reduced bias in parameter estimates due to covariate measurement error and informative censoring. We illustrate the methodology by application to a data set that consists of repeated measurements of the immunologic marker CD4 and times of diagnosis of AIDS for a cohort of anti-HIV-1 positive recipients of anti-HIV-1 positive blood transfusions. We assume a linear random effects model with subject-specific intercepts and slopes and normal errors for the true log and square root CD4 counts, and a proportional hazards model for AIDS-free survival time expressed as a function of current true CD4 value. On the square root scale, the joint approach yielded a mean slope for CD4 that was 7 per cent steeper and a log relative risk of AIDS that was 35 per cent larger than those obtained by analysis of the component sub-models separately.

Acquired Immunodeficiency Syndrome↗

PubMed2001

Managed care in the doctor's office: has the revolution stalled?

OBJECTIVE: To assess trends in the involvement of US physicians with managed care. STUDY DESIGN: Comparison of data from 2 consecutive rounds of a national survey. METHODS: Longitudinal data were obtained from the 1996/1997 (n = 12,528) and the 1998/1999 (n = 12,304) rounds of the Community Tracking Study (CTS) Physician Survey, a large, ongoing nationally representative survey of US physicians involved in patient care. Indicators used to assess involvement with managed care included global measures of managed care participation, risk contracting, exposure to financial incentives, and impact of care management tools. Changes in these measures over the 2 study periods are reported. Analyses were conducted for all physicians, as well as for primary care physicians (PCPs) and specialists separately. RESULTS: The percentage of practice revenue derived from managed care increased only modestly over the study period (from 42% to 45%). Mean numbers of managed care contracts per physician increased minimally (from 12 to 13). Trends in acceptance of capitation and exposure to financial incentives remained stable over the study period. Among PCPs, employment in staff/group health maintenance organizations declined slightly, whereas gatekeeping function increased modestly. Among care management tools, only treatment guidelines had a significantly increased impact on medical practice, primarily among PCPs (from 46% to 52%; P < .001). CONCLUSIONS: Many aspects of managed care leveled off between 1996 and 1999 in ways not accurately reflected by plan enrollment patterns. This "flattening of the curve" trend appears to hold generally across multiple measures. A stalling of the managed care "revolution," if it is sustained, may portend future escalation in healthcare costs.

Capitation Fee↗

PubMed2001

On the use of Cox regression in the presence of an irregularly observed time-dependent covariate.

We consider the joint modelling of longitudinal and event time data. The longitudinal data are irregularly collected and the event times are subject to right censoring. Most methods described in the literature are quite complex and do not belong to the standard statistical tools. We propose a more practical approach using Cox regression with time-dependent covariates. Since the longitudinal data are observed irregularly, we have to account for differences in observation frequency between individual patients. Therefore, the time elapsed since last observation (TEL) is added to the model. TEL and its interaction with the time-dependent covariate show a strong effect on the hazard. The latter indicates that older recordings have less impact than recent recordings. Pros and cons of this methodology are discussed and a simulation study is performed to study the effect of TEL on the hazard. The fitted Cox model serves as a starting point for the prediction of future patient's events. Our method is applied to a study on chronic myeloid leukaemia (CML) with longitudinal white blood cell counts (WBC) as time-dependent covariate and patient's death as event.

Analysis of Variance↗

PubMed2005

Parameter evaluation and model validation of ozone exposure assessment using Harvard Southern California Chronic Ozone Exposure Study data.

To examine factors influencing long-term ozone (O3) exposures by children living in urban communities, the authors analyzed longitudinal data on personal, indoor, and outdoor O3 concentrations, as well as related housing and other questionnaire information collected in the one-year-long Harvard Southern California Chronic Ozone Exposure Study. Of 224 children contained in the original data set, 160 children were found to have longitudinal measurements of O3 concentrations in at least six months of 12 months of the study period. Data for these children were randomly split into two equal sets: one for model development and the other for model validation. Mixed models with various variance-covariance structures were developed to evaluate statistically important predictors for chronic personal ozone exposures. Model predictions were then validated against the field measurements using an empirical best-linear unbiased prediction technique. The results of model fitting showed that the most important predictors for personal ozone exposure include indoor O3 concentration, central ambient O3 concentration, outdoor O3 concentration, season, gender, outdoor time, house fan usage, and the presence of a gas range in the house. Hierarchical models of personal O3 concentrations indicate the following levels of explanatory power for each of the predictive models: indoor and outdoor O3 concentrations plus questionnaire variables, central and indoor O3 concentrations plus questionnaire variables, indoor O3 concentrations plus questionnaire variables, central O3 concentrations plus questionnaire variables, and questionnaire data alone on time activity and housing characteristics. These results provide important information on key predictors of chronic human exposures to ambient O3 for children and offer insights into how to reliably and cost-effectively predict personal O3 exposures in the future. Furthermore, the techniques and findings derived from this study also have strong implications for selecting the most reliable and cost-effective exposure study design and modeling approaches for other ambient pollutants, such as fine particulate matter and selected urban air toxics.

Air Pollutants↗

PubMed1986

Changing relationships between stature and lung volumes during puberty.

In a follow-up study the relationship between growth in body dimensions and in lung volumes during the adolescent growth spurt was studied in 149 girls and 477 boys, aged 11.5-14.0 years at the start of the study. Total lung capacity (TLC), residual volume, vital capacity (VC) and series dead space were measured twice a year for 6 years. When analyzed cross-sectionally lung volumes can be described by a power function of stature, both for each set of half-yearly measurements and when all data are pooled. The powers were close to 3, increasing at each time of measurement in boys and decreasing in girls. These trends reflect that in each subject the growth spurt does not start at the same age, and that individual growth occurs non-linearly along a steeper line than found in the cross-section. Using simple allometric relationships between stature and lung volumes, volume predictions are too high in the youngest age group, and too low in the oldest adolescents. Including age in the regression equation removes this trend in the cross-sectional data, and for VC and TLC also in the longitudinal data.

Adolescent↗

PubMed1990

Fostering hope in terminally-ill people.

This study explored the meaning of hope and identified strategies that are used to foster hope in a convenience sample of 30 terminally-ill adults using the technique of methodological triangulation (interview, Herth Hope Index and Background Data Form). Cross-sectional data were collected on 20 of the subjects, and longitudinal data were collected on 10 of the subjects in order to provide a clearer understanding of the hoping process during the dying trajectory. Hope was defined as an inner power directed toward enrichment of 'being'. With the exception of those diagnosed with AIDS, overall hope levels among subjects were high and were found to remain stable over time and across the background variables. Seven hope-fostering categories and three hope-hindering categories were identified based on the interview responses. The findings could serve as a guide for the development of interventions to foster hope in terminally-ill people.

Adaptation, Psychological↗

PubMed1995

Instrumental activities of daily living related to impairments and functional limitations in 70-year-olds and changes between 70 and 76 years of age.

The aim of this study was to analyse in particular dependence in instrumental daily life activities (I-ADLs) and its association with physical impairments and functional limitations in the elderly. The study was based on cross-sectional data on 70-year-olds (n = 602) and longitudinal data on subjects followed up to the age of 76 (n = 371). Persons dependent in ADL had lower values in maximum walking speed, grip strength, knee extensor strength, stair climbing capacity and in forward reach, compared with those who were independent in ADL. Walking speed in both women and men and sight impairment in men had the greatest influence on dependence in ADL. Possible critical levels for disability in ADL are discussed, as persons who developed dependence between 70 and 76 already had a lower capacity in walking speed and knee extensor strength at age 70 than persons who retained their independence in ADL.

Activities of Daily Living↗

PubMed2005

A dynamic investigation of cognitive dedifferentiation with control for retest: evidence from the Swiss Interdisciplinary Longitudinal Study on the Oldest Old.

Empirical examinations of the hypothesis of dedifferentiation of cognitive abilities in old and very old age (a) do not account for possible retest effects, which consequently may yield biased estimates of age effects, and (b) focus on time-independent relations (e.g., number of latent constructs, correlations between latent or measured variables). The authors applied a structural equation model with statistical control for retest effects to investigate the dynamic relations between a marker of perceptual speed (cross out) and a marker of verbal fluency (category-fruits). Longitudinal data are from 5 waves of the Swiss Interdisciplinary Longitudinal Study on the Oldest Old (N = 377, baseline age range = 79.5- 84.5 years). The authors found that, independently of retest effects, performance on the cross-out task affected changes in performance on the category task while the opposite did not hold true. This analytical technique could be applied to various markers of broad fluid-mechanic and broad crystallized-pragmatic components of cognition.

Aged↗

PubMedDate not supplied

Cross-sectionally and longitudinally balanced effects of processing speed on intellectual abilities.

The processing speed theory of cognitive aging states that declines in intellectual abilities other than processing speed are mainly due to a slowing of processing speed. Cross-sectional studies have provided support for the processing speed theory as for age-related cognitive differences. Longitudinal studies, in turn, have provided weaker support for the processing speed theory as for cognitive age changes. The present study aims to reconcile this discrepancy of cross-sectional and longitudinal results by constructing a "fair" test of the processing speed theory, i.e., a test that balances the cross-sectional age range and the time period covered longitudinally. Data from 83 older adults came from the Bonn Longitudinal Study on Aging. Using hierarchical linear models, it is shown that, although cross-sectional age differences and longitudinal changes in the intellectual abilities were equal, processing speed only attenuated cross-sectional age effects in cognition but virtually did not reduce longitudinal change effects in cognition. This persisting difference in the explanatory power of processing speed regarding age-related differences and age-related changes is discussed with reference to other longitudinal studies and statistical issues regarding cross-sectional and longitudinal studies of aging.

Aged↗

PubMed2006

Changes in outlet densities affect violence rates.

BACKGROUND: Previous assessments of empirical relationships between alcohol outlets and rates of interpersonal violence have been conducted using cross-sectional spatial data, data collected across small geographic units such as Census Tracts and zip codes. These assessments demonstrate that the availability of alcohol, measured by the number and types of alcohol outlets, is related to violence. These analyses have examined many potential confounds of the outlets-violence connection (i.e., population and place characteristics) and statistically corrected for biases that arise in analyses of spatial data. The current study contributes the first observation of longitudinal relationships between alcohol outlets and violence. METHOD: The study examined longitudinal data from 581 consistently defined zip code areas represented in the California Index Locations Database, a geographic information system that coordinates population and ecological data with spatial attributes for areas across the state. Six years of data were collected on features of local populations (e.g., household size) and places (e.g., retail markets) thought to be related to 1 measure of violence (i.e., hospital discharges related to violent assaults). Assault rates were related to changes in population and place characteristics using random effects models with controls for spatial autocorrelation (n x t = 3,486 observations). Changes in population and place characteristics of bordering (spatial lagged) areas were also considered. RESULTS: Lower median household income and greater percentages of minorities (African American, Hispanic, and Asian) were related to increased rates of violence. Ten percent increases in numbers of off-premise outlets and bars were related to 1.67 and 2.06% increases in violence rates across local and lagged spatial areas. Every 6 outlets accounted for 1 additional violent assault that resulted in at least 1 overnight stay at hospital. These effects increased with larger male populations, doubling with every 3% increase in percent males. CONCLUSION: Assault rates were most strongly related to median household incomes and minority populations within zip code areas. Controlling for changes in assault rates related to these measures, greater numbers of licensed alcohol retail establishments, especially bars and off-premise outlets, were related to rates of assault. Failures to regulate the growth in numbers of bars will increase rates of violence, especially in urban areas.

California↗

PubMed1986

Probing considerations in relation to susceptibility to periodontal breakdown.

Both epidemiological and clinical studies indicate that not all individuals are equally susceptible to periodontal breakdown. Therefore, the clinical differences were investigated between subjects highly susceptible and subjects insusceptible to periodontal breakdown. The highly susceptible group consisted of patients with a diagnosis of juvenile periodontitis. The insusceptible group consisted of older individuals with gross amounts of plaque and no periodontal breakdown. Results indicated that a high value of the bleeding/plaque ratio may possibly act as a prognostic indicator for periodontal breakdown. However, longitudinal data are indispensable for substantiation of this hypothesis. Since longitudinal research takes many years, the experimental gingivitis model was chosen for further investigation. 4 groups of individuals were selected on the basis of a different history of inflammatory periodontal disease: 2 younger age groups without periodontal breakdown, having either a low or a high bleeding/plaque ratio--a hypothetically susceptible and a hypothetically insusceptible group, respectively; one older age group with presence of gross amounts of plaque, no periodontal breakdown and a low bleeding/plaque ratio--an insusceptible group; and an adult group who previously suffered from severe periodontal disease--a susceptible group. Results of the experimental gingivitis studies indicated that the older insusceptible group developed only small amounts of bleeding, whereas the younger hypothetically insusceptible group developed a comparable low bleeding index. The younger hypothetically susceptible group developed a much higher bleeding index comparable to that of the susceptible group, the periodontal patients. In conclusion, comparison of the results of the experimental gingivitis studies in subjects with differing histories of inflammatory periodontal disease supports the concept that the bleeding/plaque ratio may act as a prognostic indicator for periodontal breakdown.

Adolescent↗

PubMed2005

Selected lessons learned from the Dialysis Outcomes and Practice Patterns Study (DOPPS).

The Dialysis Outcomes and Practice Patterns Study (DOPPS) is a prospective, observational study of the relationships between hemodialysis (HD) patient outcomes and HD treatment practices. The DOPPS began in 1996 in the United States, expanding to France, Germany, Italy, Japan, Spain, and the United Kingdom in 1998-1999, and then to Australia, Belgium, Canada, New Zealand, and Sweden in 2002. More than 300 dialysis units have participated in the DOPPS since 1996, with mortality data collected from nearly 90,000HD patients and detailed longitudinal data from nearly 30,000 HD patients. Large sample size and the large treatment practice variation observed in the DOPPS--given its international scope of participation--provide strong statistical power to investigate many different HD practices. Furthermore, the detailed patient data collected in the DOPPS allow relationships to account for differences in a large number of patient characteristics. More than 55 papers have been published from the DOPPS; here we provide a summary of selected DOPPS findings regarding nutrition, mineral metabolism, anemia management, vascular access, depression, and use of multivitamins and statins.

Anemia↗

PubMed1985

Employment, marital status and alcohol consumption of young Canadian men.

This article focuses on heavy alcohol consumption among young Canadian men drinkers aged 15-29 and examines how employment status and marital status interact with age. The study found that the highest percentages of heavy drinkers occurred in men over the age of 18 who are single (divorced, separated or never married) and in the labor force, whether employed or unemployed. This study, based on cohort data, generated hypotheses that need to be tested with longitudinal data in order to better understand developmental differences and other factors that affect drinking practices.

Adolescent↗

PubMed2003

Does perceived discrimination affect health? Longitudinal relationships between work discrimination and women's physical and emotional health.

This study uses longitudinal data to examine the causal relationships between perceived work discrimination and women's physical and emotional health. Using data on 1,778 employed women in the National Longitudinal Survey of Mature Women, we investigate the structural and individual characteristics that predict later perceptions of discrimination and the effects of those perceptions on subsequent health. We find that perceptions of discrimination are influenced by job attitudes, prior experiences of discrimination, and work contexts, but prior health is not related to later perceptions. However, perceptions of discrimination do impact subsequent health, and these effects remain significant after controlling for prior emotional health, physical health limitations, discrimination, and job characteristics. Overall, the results provide even stronger support for the health impact of workplace discrimination and suggest a need for further longitudinal analyses of causes and consequences of perceived discrimination.

Adult↗

PubMed1988

Design of clinical database management systems and associated software to facilitate medical statistical research.

Clinical databases are growing rapidly. The clinical database is heavily used for medical research in many settings. This paper discusses design features for medical databases that facilitate their use for research. The database management system should allow complex data structures, have a syntax-facilitating collection of longitudinal data, interface with major statistical software packages, allow an extensive data dictionary, conveniently merge files, facilitate archival documentation, have an associated data entry system that allows complex logical checking, and have coordinated mainframe and microcomputer software.

Biometry↗

PubMed1994

Predicting adult stature without using skeletal age: the Khamis-Roche method.

STUDY OBJECTIVE: To obtain reliable and accurate predictions of adult stature in white American children who are free of disease without using skeletal age. DESIGN: Apply a modification of the Roche-Wainer-Thissen stature prediction model to a sample of white American children. SETTING: Longitudinal data (every 6 months) from participants in the Fels Longitudinal Study were used for the development of the stature prediction model. PARTICIPANTS: Residents of Southwest Ohio, 223 white males and 210 white females, at the time of their enrollment into the Fels Longitudinal Study. MEASUREMENTS AND RESULTS: The errors of the proposed method, which does not use skeletal age as a predictor variable, are only slightly larger than those for the Roche-Wainer-Thissen method which uses skeletal age as a predictor variable. CONCLUSIONS: Adult stature predictions are needed commonly but the current methods are difficult to apply because they require a skeletal age assessed by a modern method. The Khamis-Roche method predicts adult stature in the absence of skeletal age with only a slight deterioration in accuracy and reliability. The applicability of the Khamis-Roche method is limited to white American children without pathologic conditions that alter the potential for growth in stature, but it should be useful for white children who are unusual in stature or in levels of maturity for age.

Adolescent↗

PubMed1998

Traversing the menopause: changes in energy expenditure and body composition.

The menopause transition is associated with several physiological changes that may impact women's health outcome. Among the changes associated with the loss of ovarian function is an increased risk of metabolic and cardiovascular disease. The present review focuses on changes in energy expenditure, body composition and body fat distribution during the postmenopausal transition. Previous work indicates that the most important component of total daily expenditure, resting metabolic rate, may be reduced by the menopause, independently of the effects of the normal aging process. This effect is mainly attributable to a decrease in fat-free mass. The energy expenditure associated with physical activity is the most variable component of total daily energy expenditure. However, small changes in this component may have a substantial impact on body composition. Longitudinal data from our laboratory indicate that the menopause transition also leads to significant decreases in physical activity energy expenditure. The changes in body composition that accompany the menopause transition have been studied by several groups and, although some studies suggested increases in body mass index or total body fat mass with the menopause, currently available cross-sectional data preclude a firm conclusion. Nevertheless, results from our longitudinal study showed significant increases in fat mass with the menopause. The accumulation of abdominal fat, which may be a better correlate of the comorbidities associated with obesity, has also been shown to be accelerated by the menopause transition. In this regard, it has been shown that treatment with hormone replacement therapy prevents the increase in the rate of abdominal adipose tissue accumulation that was noted with the menopause. Thus, it appears that the loss of ovarian function induces a reduction in resting metabolic rate, physical activity energy expenditure, fat-free mass, and an increase in fat mass and abdominal adipose tissue accumulation. These modifications probably contribute to the increased risk of cardiovascular disease of postmenopausal women.

Adipose Tissue↗