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PubMed1996

The Alzheimer's Disease Assessment Scale.

This article reviews longitudinal data collected from patients with Alzheimer's disease (AD) that are relevant to the design and interpretation of clinical treatment trials. Longitudinal data from patients tested with the Alzheimer's Disease Assessment Scale demonstrate that cognitive symptoms, including memory loss, dysphasia, and dyspraxia, worsen relentlessly over time with the rate of change depending upon baseline dementia severity. Noncognitive symptoms, such as agitation, depressed mood, and psychosis, are episodic, do not necessarily worsen over time, and tend not to be highly correlated with one another. The reliability of cognitive change measures increases with follow-up duration so that the likelihood of detecting drug effects on the rate of cognitive deterioration is greater with longer treatment trials. Functional measures of activities of daily living are difficult to standardize for AD patients but are important for determining the overall clinical and economic impact of AD treatments.

Activities of Daily Living↗
PubMed2004

The application of multilevel modeling in the analysis of longitudinal periodontal data--part I: absolute levels of disease.

BACKGROUND: Statistical analyses of periodontal data that average site measurements to subject mean values are unable to explore the site-specific nature of periodontal diseases. Multilevel modeling (MLM) overcomes this, taking hierarchical structure into account. MLM was used to investigate longitudinal relationships between the outcomes of lifetime cumulative attachment loss (LCAL) and probing depth (PD) in relation to potential risk factors for periodontal disease progression. METHODS: One hundred males (mean age 17 years) received a comprehensive periodontal examination at baseline and at 12 and 30 months. The resulting data were analyzed in two stages. In stage one (reported here), the absolute levels of disease were analyzed in relation to potential risk factors; in stage two (reported in a second paper), changes in disease patterns over time were analyzed in relation to the same risk factors. Each approach yielded substantially different insights. RESULTS: For absolute levels of disease, subject-level risk factors (covariates) had limited prediction for LCAL/PD throughout the 30-month observation period. Tooth position demonstrated a near linear relationship for both outcomes, with disease increasing from anterior to posterior teeth. Sites with subgingival calculus and bleeding on probing demonstrated more LCAL and PD, and supragingival calculus had an apparently protective effect. Covariates had more "explanatory power" for the variation in PD than for the variation in LCAL, suggesting that LCAL and PD might be generally associated with a different profile of covariates. CONCLUSION: This study provides, for a relatively young cohort, considerable insights into the factors associated with early-life periodontal disease and its progression at all levels of the natural hierarchy of sites within teeth within subjects.

Adolescent↗
PubMedDate not supplied

Age-related slowing on the Digit Symbol task: longitudinal and cross-sectional analyses.

It is generally known that slowing on tasks like the Digit Symbol Substitution task occurs with age. However, simultaneous cross-sectional and longitudinal data are rare. The results from the cross-sectional analysis of Digit Symbol performance with age are compared to results from two occasion longitudinal analyses on the same task. The longitudinal data were obtained from 79 participants who were retested after 7 years and were between the ages of 48 and 73 years old at Time 1. Results indicated that the pattern of actual change observed in the longitudinal analyses replicated the simulated change indicated in the cross-sectional analysis. Antecedents were examined using the original cross-sectional sample of 150 participants. Significant relationships with Digit Symbol performance were found for age, education, and gender, but not for ratings of physical health.

Aged↗
PubMedDate not supplied

Some statistical issues in the analyses of data from longitudinal studies of elderly chronic care populations.

OBJECTIVE: This article discusses broad statistical issues common to much medical research: intent-to-treat analysis vs. completers analysis; clustered hierarchical and repeated-measures data; missing data and dropouts; and assessment of direct, indirect, and total effects. Traditional approaches and statistical techniques are reviewed and contrasted with modern methods for analysis of medical studies. METHOD: The concepts are introduced and discussed in general terms; they are illustrated with an example. The example comes from a study of the effect of residence in special care units (SCUs) for demented elderly on the daily function of nursing homes residents. More than 700 residents from 22 nursing facilities, residing in either an SCU or a non-SCU were assessed three times at approximate 6-month intervals. RESULTS: Results from both the application of traditional statistical techniques and modern methods for the analysis of repeated-measures of hierarchical multicenter data are presented, interpreted, and compared. Advantages and shortcomings of these approaches are discussed. CONCLUSION: This article advocates the use of mixed models and proper causal reasoning and terminology in the analysis and publication of results from studies on aging and life course.

Activities of Daily Living↗
PubMed1994

Timing of eruption of permanent teeth: standard Finnish patient documents.

Current standards for the eruption of teeth are constructed mostly on the basis of cross-sectional data. The aim here was to analyze the suitability of the standard patient documents created for health center dental care purposes for the collection of longitudinal data on tooth emergence. Copies of the oral health records of the 911 children born in 1970 and 1971 and in 1980 and 1981 living in three rural communities in Finland were re-examined and analyzed using a specially compiled computer program. The means and standard deviations are in line with previous results. The sex difference in emergence timing ranged from 0.1 to 1.0 years for the various teeth. The emergence of the teeth of the second phase of the mixed dentition was later in the children living in an endemic fluoride area, this difference being statistically greater for the boys than for the girls (95% Cl for differences between means was used to evaluate statistical significance). A secular trend in the eruption of permanent teeth was found between 1970 and 1980. Patient documents are shown to be suitable for the collection of longitudinal data on dental emergence.

Adolescent↗
PubMed1987

Treatment for strabismus in cerebral palsy.

The efficacy of extraocular muscle surgery and visual training for strabismus, in a limited number of cerebral palsy patients, are examined. Longitudinal data on tropias are presented for surgically treated patients. Short-term effects of visual training for another group of patients are described. Longitudinal data on tropias are presented for a group of cerebral palsy patients who received no strabismus therapy.

Adolescent↗
PubMed2006

Long-term Food Stamp Program participation is positively related to simultaneous overweight in young daughters and obesity in mothers.

Previous research using longitudinal data has found a positive and significant relationship between Food Stamp Program (FSP) participation and overweight in young girls and obesity in low-income women. This paper examined whether these relationships occurred simultaneously for members of the same family using longitudinal data on young (aged 4.5-11.5 y) girls and their mothers from the National Longitudinal Survey of Youth 1979. The results of ordinary least squares models that included detailed measures of individual, family, and environment characteristics and daughter or mother fixed effects indicated that all of the positive association between long-term FSP participation and overweight in daughters was accounted for by the association between long-term FSP participation and simultaneous overweight in daughters and obesity in mothers. Similarly, all of the positive association between long-term FSP participation and obesity in mothers was accounted for by the association between long-term FSP participation and simultaneous obesity in mothers and overweight in at least 1 young daughter. These results suggest that the relationship between long-term FSP participation and weight is a family phenomenon.

Body Weight↗
PubMed1999

Measuring change: mixed Markov models for ordinal panel data.

In an analysis of longitudinal data it is important to distinguish between dependencies caused by within- and between-subject variability. This paper presents mixed Markov models for ordinal data that take into account both sources of variation. In addition, covariates that may capture differences among panel members and time-specific changes are also incorporated in the model. The model is derived by specifying an observation-driven process at the individual level and allowing for parametric or semi-parametric representations of random parameter variation across the units of analysis. As a result, the approach is well suited for modelling ordinal panel data with a large number of time points. In an application a three-week diary study is analysed to test hypotheses about the relationships between emotions and personality factors over time.

Affect↗
PubMed1988

A longitudinal study of functional change and mortality in the United States.

Studies of functional impairments in the U.S. elderly population have tended to rely on prevalence estimates from nationally representative health and institutional surveys. These prevalence estimates generally show higher rates of disability for females than males. Unfortunately, prevalence estimates can be misleading when one attempts to assess the risks of certain types of health event transitions for individuals. This study directly examined the individual transitions both into and out of functionally impaired states using longitudinal data from the 1982 and 1984 National Long Term Care Surveys (NLTCS). The data show that, even at very high levels of impairment, there are significant numbers of community residents who apparently manifest long-term improvement in functioning. The longitudinal data also show that the risks of becoming disabled are roughly the same for males and females. This suggests that sex differences in the national prevalence of disabilities arise from the greater longevity of females at any given level of age and functional impairment.

Activities of Daily Living↗
PubMed1999

Dynamic paradigms for human mortality and aging.

Hazard models are often applied to mortality data of humans and other species so that the parameter estimates made for those models can be used to make inferences about the biology, and comparative biology, of aging processes. Enough longitudinal data on physiological and functional changes in humans now exist to know that the age trajectory of the physiological state of individuals is multidimensional, stochastic, and plastic. Thus, to fully assess the biological significance of existing longitudinal data on human aging and mortality processes, multivariate stochastic process models must be developed that are biologically detailed and valid. This requires assessing genetic mechanisms controlling human longevity and rates of aging, developing models of how those traits may have evolved, and developing statistical methods for identifying gene environment interactions. This article examines the theoretical basis for such models and the biological rationale of their parametric structure. Several examples are given.

Aged↗
PubMed2003

Statistical significance analysis of longitudinal gene expression data.

MOTIVATION: Time-course microarray experiments are designed to study biological processes in a temporal fashion. Longitudinal gene expression data arise when biological samples taken from the same subject at different time points are used to measure the gene expression levels. It has been observed that the gene expression patterns of samples of a given tumor measured at different time points are likely to be much more similar to each other than are the expression patterns of tumor samples of the same type taken from different subjects. In statistics, this phenomenon is called the within-subject correlation of repeated measurements on the same subject, and the resulting data are called longitudinal data. It is well known in other applications that valid statistical analyses have to appropriately take account of the possible within-subject correlation in longitudinal data. RESULTS: We apply estimating equation techniques to construct a robust statistic, which is a variant of the robust Wald statistic and accounts for the potential within-subject correlation of longitudinal gene expression data, to detect genes with temporal changes in expression. We associate significance levels to the proposed statistic by either incorporating the idea of the significance analysis of microarrays method or using the mixture model method to identify significant genes. The utility of the statistic is demonstrated by applying it to an important study of osteoblast lineage-specific differentiation. Using simulated data, we also show pitfalls in drawing statistical inference when the within-subject correlation in longitudinal gene expression data is ignored.

Adaptation, Physiological↗
PubMed2006

Are there distinctive trajectory groups in substance abuse remission over 10 years? An application of the group-based modeling approach.

This paper introduces to mental health services and evaluation researchers a method for analyzing longitudinal data: a group-based modeling approach for applied research. We present the basic formulations of the model and illustrate its application by analyzing the 10-year longitudinal data on substance abuse remission from the New Hampshire Dual Disorders Study. The basic features of the approach are: identifying latent groups with distinctive trajectories, estimating the proportion of the population in each group, linking individual-level covariates to group membership, assigning individuals to different groups, and creating group profiles based on posterior probabilities. We also discuss cautions and the controversies surrounding this approach. The major findings include four groups with distinct trajectories of remission from substance abuse.

Female↗
PubMed2003

A half century of longitudinal methods in social gerontology: evidence of change in the journal.

OBJECTIVES: With a focus on the use of longitudinal data, this study reviews trends in the quantitative analysis of social science data on aging during the past half century. METHODS: A content analysis was performed on 227 articles from 12 volumes that were systematically sampled from the Journal of Gerontology: Social Sciences to examine change in the type of data and quantitative methods used (1946-2000). RESULTS: Cross-sectional analysis remains the single most frequent type of study, but the publication of analyses based on longitudinal panel data increased appreciably over the five decades studied. There was little increase in the use of repeated cross-sectional analysis. DISCUSSION: Despite the widespread use of cross-sectional analysis, interest in data with more than one occasion of measurement has grown among social scientists who are reviewing for and publishing in the JOURNAL. Given the longitudinal data now available, social science research on aging should give more explicit attention to three issues: attrition, change in repeated measures of independent variables, and models to account for many waves of data.

Bibliometrics↗
PubMed1992

Response reliability of demographic data: a longitudinal study in Sri Lanka.

Response consistency was examined by linking the records of women interviewed in the 1982 Sri Lanka Contraceptive Prevalence Survey with records from the same individuals followed up 3 years later. Seventy-eight percent of women reported identical year of birth in the two surveys, but only 58% were consistent for age at marriage. Data on sterilisation and number of children born were highly reliable, but wives' reports on husband's age and education were relatively weak. Multivariate analysis of the effects of socioeconomic factors on consistency in age reporting confirms that education is the most influential factor related to consistency, followed by religion and husband's occupation.

Birth Rate↗
PubMed1999

Randomized clinical trial comparing the efficacy of mandibular implant-supported overdentures and conventional dentures in diabetic patients. Part III: comparisons of patient satisfaction.

STATEMENT OF PROBLEM: There is insufficient evidence to indicate the functional superiority of mandibular implant-supported overdentures to justify their use in edentulous patients. PURPOSE: This study compared the benefits perceived by patients who received a new maxillary denture and a mandibular conventional denture (CD) and an implant-supported overdenture (IOD). METHOD: New maxillary and mandibular dentures were delivered to 89 diabetic denture wearers with clinically acceptable metabolic control who treated their diabetes either with insulin (IT) or without insulin (NIT). Of the 89 patients, 37 received maxillary and mandibular CDs and 52 received a maxillary CD and an IOD. Two questionnaires with categorical responses were used; the first contained 13 questions to ascertain a patient's absolute assessments of original dentures at entry and study dentures at 6- and 24-months after treatment completion; the second questionnaire had 11 questions that assessed the relative change perceived by patients with study dentures. Of the 78 patients who completed the posttreatment (PT) assessments at 6 months, 68 patients provided longitudinal data for questionnaire I and cross-sectional data for questionnaire II. In addition, 46 patients (18 CD and 28 IOD) also provided PT assessments at 24 months. RESULTS: Both mean scores and percentage distributions of longitudinal data for questionnaire I showed perceptual improvements with both types of study dentures. Improvements were higher in the IOD than in the CD group. Mean scores failed to show any significant differences between the 2 treatment groups. The only significant difference was found in the change in percentage distributions for perceptual chewing ability in favor of the IOD group. Even this advantage was lost at 24 months. With the comparative questionnaire, a higher percentage of patients in the IOD group than in the CD group perceived improvements with study dentures from their original dentures in chewing ability, chewing comfort, and denture security. However, mean differences were statistically significant in favor of the IOD group only for chewing ability and less difficulty to chew hard foods. CONCLUSION: The mandibular implant-supported overdenture offers same advantage in terms of perceived chewing function over the conventional denture.

Aged↗
PubMed2002

Bayesian modeling of incidence and progression of disease from cross-sectional data.

In the absence of longitudinal data, the current presence and severity of disease can be measured for a sample of individuals to investigate factors related to disease incidence and progression. In this article, Bayesian discrete-time stochastic models are developed for inference from cross-sectional data consisting of the age at first diagnosis, the current presence of disease, and one or more surrogates of disease severity. Semiparametric models are used for the age-specific hazards of onset and diagnosis, and a normal underlying variable approach is proposed for modeling of changes with latency time in disease severity. The model accommodates multiple surrogates of disease severity having different measurement scales and heterogeneity among individuals in disease progression. A Markov chain Monte Carlo algorithm is described for posterior computation, and the methods are applied to data from a study of uterine leiomyoma.

Age of Onset↗
PubMed1991

The Geriatric Depression Scale and Hopelessness Index: longitudinal psychometric data on frail nursing home residents.

We administered the Geriatric Depression Scale and the Hopelessness Index 18 times over a 39-wk. period to an initial sample of 76 old, frail, multiply impaired, and depressed nursing home residents participating in a longitudinal quasi-experimental study on the effects of cognitive group interventions on cognition, depression , hopelessness, and life satisfaction. As no changes over time were observed on the outcome variables of geriatric depression and hopelessness, the stability of the instruments' internal consistency was examined longitudinally. For the Geriatric Depression Scale, Kuder-Richardson KR-20 coefficients ranged from .69 to .88, with a mean of .82 (SD = .05). Coefficients for the Hopelessness Index were between .72 and .86, with a mean of .80 (SD = .04). We conclude that both instruments give reliable measurements of geriatric depression and hopelessness in old, frail, and depressed nursing home residents.

Aged↗