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PubMed1992

The New Beneficiary Data System: the first phase.

The completion of field work for the 1991 New Beneficiary Followup has transformed the 1982 New Beneficiary Survey from a simple cross-sectional data collection effort to the first step in a new longitudinal data base, which is further enriched with information obtained from administrative records. The resulting New Beneficiary Data System will make it possible to develop a better understanding of the dynamics of the experience of aged and disabled populations over the long term. A review of 24 reports prepared by Social Security Administration analysts who have used data from the first wave of interviews reveals a great deal of variation among different types of beneficiaries with respect to income, assets, pensions, work, health, and other factors. These reports provide a useful context for examining patterns of stability and change in the beneficiary population as the data from administrative records and later interviews are added to the data base and used to address issues of policy interest.

Aged↗

PubMed2001

An application of multilevel modelling to longitudinal periodontal research data.

OBJECTIVE: To introduce the concepts of random coefficient multilevel models through an application to periodontal research data. BASIC RESEARCH DESIGN: Multilevel models with random coefficients are illustrated using periodontal data that comprise four levels: repeated measurements at level-1, sites at level-2, teeth at level-3, and subjects at level-4. The study explores random coefficient models--where random variation occurs about explanatory variable coefficients. Outcomes considered are lifetime cumulative attachment loss and pocket probing depth. PARTICIPANTS: The study data were taken from a survey of periodontal disease involving 100 white male trainee engineers aged between 16 and 20 entering the apprentice training school at the Royal Air Force-Halton, UK. RESULTS: The application of multilevel modelling to longitudinal data provides a new way of exploring old problems. The multilevel random coefficient models provide an opportunity to examine the 'linear' and 'burst' theories of periodontal disease progression, leading to the postulation that both can be unified within the multilevel framework. CONCLUSIONS: The multilevel methodology illustrates how advances in the understanding of oral health can be achieved with the advent of new statistical methods

Adolescent↗

PubMed1992

Analysis of premature ventricular counts in long term ECG following myocardial infarction.

Frequent and recurrent ventricular premature beats (VPB's) are considered to be associated with a higher risk of sudden cardiac death, particularly for survivors of myocardial infarction (MI). The distribution of VPB's has a large probability mass at zero, and a very heavy right hand tail. In this research, we fitted a model to VPB for patients for which VPB was present. The model was fitted on the basis of a relatively large data set on MI survivors in Israel. The model was fitted by a method which is based on the generalized linear model. This method, which was introduced by Zeger and Liang, is designed for longitudinal data and uses the quasi-likelihood concept. No specific assumptions are required on the shape of the distribution of the dependent variable. The results indicate that the model fits the data quite well but underestimates the very extreme high values. This research demonstrates the applicability of generalized linear models for longitudinal non-Gaussian data. Such data often arise in medical studies. The study also points out the distributional properties of VPB counts. In particular, it shows their associations with simple clinical and epidemiological variables, and with certain time periods during the day.

Cardiac Complexes, Premature↗

PubMed2003

Changes in child survival are strongly associated with changes in malnutrition in developing countries.

Considerable evidence suggests that malnutrition affects human performance, health and survival, including physical growth, morbidity, mortality, cognitive development, reproduction, physical work capacity and risks for several adult-onset chronic diseases. In recent decades, development agencies and governments have emphasized selective interventions to improve health and nutritional status, such as immunizations, oral rehydration, antibiotics and micronutrients, with child survival as a major motivation and justification. Although the efficacy of these approaches for improving child survival has been amenable to study, providing some of the rationale for using these approaches, it has not been possible to test directly the effects of improvements in general malnutrition. The present study quantified the effects of changes in general malnutrition, as measured by child weight-for-age (WA), on changes in child survival in 59 developing countries, using aggregate, longitudinal data at national and subnational levels from 1966 to 1996. Mixed model analysis (in SAS) was used, to take advantage of the multilevel and longitudinal nature of these data sets. Changes in WA have a statistically significant effect on changes in child mortality, independent of socioeconomic and policy changes represented by the secular trend. The secular trend in mortality began earlier and leveled off at higher mortality rates in populations with a higher prevalence of malnutrition. Gaps in coverage of selective interventions are more likely and more serious in the more malnourished populations. Continued reduction in mortality will require improved targeting of selective interventions and general nutritional improvement to the most marginal populations.

Child, Preschool↗

PubMedDate not supplied

Four years of North American registry home parenteral nutrition outcome data and their implications for patient management.

The OASIS Registry started annual collection of longitudinal data on patients on home parenteral nutrition (HPN) in 1984. This report describes outcome profiles on 1594 HPN patients in seven disease categories. Analysis showed clinical outcome was principally a reflection of the underlying diagnosis. Patients with Crohn's disease, ischemic bowel disease, motility disorders, radiation enteritis, and congenital bowel dysfunction all had a fairly long-term clinical outcome, whereas those with active cancer and acquired immunodeficiency syndrome (AIDS) had a short-term outcome. The long-term group had a 3-year survival rate of 65 to 80%, they averaged 2.6 complications requiring hospitalization per year, and 49% experienced complete rehabilitation. The short-term group had a mean survival of 6 months; they averaged 4.6 complications per year and about 15% experienced complete rehabilitation. The registry data also indicated HPN was used for 19,700 patients in 1987 with therapy growth averaging about 8% per year. This growth was chiefly from new cancer patients. The number of new patients with long-term disorders in whom HPN was initiated appeared rather constant. We conclude that these clinical outcome assessments justify HPN for long-term patients, but the utility and appropriateness of HPN for the cancer and AIDS patients remains uncertain and requires further study. Medical, social, and fiscal aspects of HPN management in long-term and short-term patients appear to involve quite separate considerations.

Acquired Immunodeficiency Syndrome↗

PubMed1994

A PC program for diagnosing abnormal growth, growth velocity and acceleration from longitudinal observations.

A PC program, written in GAUSS386i, implementing Zerbe's (Growth, 43 (1979) 263-272) procedure for diagnosis on the basis of longitudinal data is described, illustrated and made available to interested readers. Given longitudinal observations on N normal individuals, this technique can be used to characterize normal growth, velocity and acceleration, and to determine whether or not a new individual can be considered normal with respect to any or all of these parameters. Missing data are allowed, and there is no requirement that the variable whose growth is being monitored has a normal distribution. The method and program are illustrated using a data set with a substantial amount of missing data. Information on obtaining a copy of the program and hardware requirements are given in the Appendix.

Algorithms↗

PubMed1983

Population estimates from longitudinal records in otherwise data-deficient settings.

Existing methods for estimating population parameters in settings of data deficiency do not provide techniques for analysis of commonly available longitudinal data. In setting where complete population data is unavailable, longitudinal data recorded for only a subset of the total population are often available (e.g., event registers, genealogies). In this article we present and evaluate models which derive population parameters for the population subgroup underlying such longitudinal data. Using the distribution of individual times until first recorded event within a measurement interval, population parameters are estimated which provide basic denominator data for analyzing event occurrence. The models which we derive are especially suited to records which may include migration and population growth trends. The use of the models is demonstrated and evaluated through an application to genealogical records for a nineteenth-century population. Possible extensions of these models and their major limitations are also discussed.

Adult↗

PubMed2001

Consequences of disease: testing the WHO International Classification of Impairments, Disabilities and Handicaps (ICIDH) model.

The International Classification of Impairments, Disabilities and Handicaps (ICIDH) model proposes that there are three consequences of disease, impairment (I), disability (D) and handicap (H) and that they are sequentially related. This paper examines first, whether I, D and H can be measured independently and second, whether there is support for the sequential or causal relationship between the three constructs. Cross-sectional data from a representative sample of 101 disabled adults and longitudinal data from 108 myocardial infarction (MI) and 68 Stroke patients were used. Standard measures of I were used for each clinical condition. Measures of D and H were derived from the British version of the Sickness Impact Profile (SIP) and additional measures of D were available for the Stroke group. Judges classified SIP items according to ICIDH definitions of D and H. Correlation, Confirmatory Factor Analyses and Path Analyses were used to examine the main hypotheses. Valid measures of D and H were derived and there was evidence of separation of the three constructs for the Stroke patients but not for the other groups. For both Stroke and MI, I was not predictive of D and H. For Stroke, the best path model included a path from D to H, but not from H to D and this was found for self-report and performance measures of D. Using these measures, the ICIDH model was supported in that D predicted H for stroke, but there was no support for a path between I and D or between I and H. Further it was not always possible to distinguish the three constructs. Possible limitations in the measures and in the ICIDH model as a testable scientific model are discussed.

Activities of Daily Living↗

PubMed2006

Latent difference score approach to longitudinal trauma research.

In this article, the authors introduce a latent difference score (LDS) approach to analyzing longitudinal data in trauma research. The LDS approach accounts for internal sources of change in an outcome variable, including the influence of prior status on subsequent levels of that variable and the tendency for individuals to experience natural change (e.g., a natural decrease in posttraumatic stress disorder [PTSD] symptoms over time). Under traditional model assumptions, the LDSs are maximally reliable and therefore less likely to introduce biases into model testing. The authors illustrate the method using a sample of children who experienced significant burns or other injuries to examine potential influences (i.e., age of child-adolescent at time of trauma and ongoing family strains) on PTSD symptom severity over time.

Adolescent↗

PubMed2006

Money and mental wellbeing: a longitudinal study of medium-sized lottery wins.

One of the famous questions in social science is whether money makes people happy. We offer new evidence by using longitudinal data on a random sample of Britons who receive medium-sized lottery wins of between 1000 pounds and 120,000 pounds (that is, up to approximately US$ 200,000). When compared to two control groups -- one with no wins and the other with small wins -- these individuals go on eventually to exhibit significantly better psychological health. Two years after a lottery win, the average measured improvement in mental wellbeing is 1.4 GHQ points.

Data Collection↗

PubMed1998

Modeling development of sleep-wake behaviors: I. Using the mixed general linear model.

The purpose of this paper is to demonstrate the use of the mixed general linear model (MixMod) for modeling development of sleep-wake behaviors in preterm infants. The mixed general linear model allows the concurrent identification of both group and individual developmental patterns in longitudinal data sets with inconsistently timed data, irregularly timed data, and randomly missing values. This statistical technique is well suited to data from preterm infants because these infants enter and leave longitudinal studies at varying times depending on their health status. One sleep organizational variable--the regularity of respiration in quiet sleep--obtained from a study of 37 preterm infants was used as an example. Seven infant characteristics were used as covariates. The various steps involved in conducting a mixed model analysis of this variable are illustrated. The strengths and limitations of this technique are discussed.

Aging↗

PubMed2002

Estimating the distribution of worm burden and egg excretion of Schistosoma japonicum by risk group in Sichuan Province, China.

During autumn 2000 an extensive cross-sectional survey of the prevalence of Schistosomiasis japonicum was conducted among about 4000 villagers within 20 villages in the Anning River Valley located in the southwestern Sichuan Province. Two procedures were used to assess infection status, the Kato-Katz thick smear procedure and a miracidia hatch test. Whereas the Kato-Katz procedure provides information on both prevalence and intensity, the hatch test provides only prevalence data, albeit on a much larger volume of stool. In addition, we performed Kato-Katz smears for 15 consecutive samples on a subset of 15 individuals. The proportion of both hatch-test and Kato-Katz positive individuals in the larger cross-sectional survey was 25%. The goal of the study was to estimate both the egg and worm distributions among risk groups using both the hatch and Kato-Katz tests from the cross-sectional data and the repeated Kato-Katz smears from the longitudinal data sets. As a prelude to parameter estimation, individuals were classified into risk groups by natural village and occupation; the proportion of Kato-Katz positive subjects among the risk groups varied from 10% to 60%. We used the statistical model of de Vlas et al. (1992) and Bayesian techniques to derive both estimates of and inference about the worm and egg distribution parameters. The parameter estimates imply (1) similar eggs per gram stool (e.p.g.) per worm pair compared with earlier estimates, (2) a range of worm burdens among the risk groups and (3) estimates of risk heterogeneity within groups is sensitive to prior information on the within-person variability in egg excretion.

Age Factors↗

PubMed1997

Opportunities and difficulties in long-term studies of growth.

Overviews are presented of the University of Melbourne Child Growth Study and of the Fels Longitudinal Study; each of these studies had a major focus on the growth and maturation of children. Planning, study design, logistics and staffing varied between these studies, but each led to exciting research opportunities that can exist only when longitudinal data are available. There are important differences between these studies in the types of participants, ages at examinations, the variables measured, some topics of central concern, and in funding. In each study, research productivity was low in the early years, the retention of participants was a major concern, and it was necessary to maintain a balance between data collection, data management, and data analysis. More such studies are needed that focus on particular population groups and topic areas and that utilize the lessons of the past to maximize the chances of future success.

Adolescent↗

PubMed2000

Viral genetic heterogeneity in HIV-1-infected individuals is associated with increasing use of HAART and higher viremia.

OBJECTIVE: To assess the correlation between the outgrowth of mutant viruses (viral genetic heterogeneity), highly active antiretroviral therapy (HAART), and plasma HIV-1 RNA in a population-based observational cohort study. DESIGN: The study population consisted of 42 HIV-1-infected individuals receiving at least two nucleotide reverse transcriptase (RT) inhibitors and one or more protease inhibitors at study entry. There were no restrictions on antiretroviral therapy after enrollment. METHODS: Plasma samples were obtained from subjects at baseline, at therapy changes, and at quarterly intervals for quantitation of HIV-1 RNA levels and for sequence determination of the entire protease coding region and the first 235 codons of the reverse transcriptase coding region. Data were analyzed using the generalized estimating equation method for longitudinal data and using linear regression analysis. RESULTS: With increased time on HAART there were significant increases in the number of total HIV-1 mutations in the regions sequenced (P = 0.010). There were significant correlations between the increases in the plasma HIV-1 RNA levels and the numbers of total mutations and reverse transcriptase mutations (P = 0.007 and 0.021, respectively). CONCLUSIONS: The number of HIV-1 mutations increased over time. Failure of HAART in this study population was correlated with outgrowth of virus with numerous mutations in the reverse transcriptase and protease coding regions. Phenotypic results correlated with genotypic results, showing decreased susceptibility to antiretrovirals over time in the majority of this population during HAART. Both synonymous and non-synonymous mutations were observed, with a higher incidence of non-synonymous mutations occurring at codons associated with drug resistance.

Adult↗

PubMed2003

The role of blood pressure variability in end-organ damage.

The ultimate goal when treating high blood pressure is to reduce the incidence of end-organ damage and prevent cardiovascular disease, and thus reduce the incidence of premature death. Cuff blood pressure measurements have some prognostic value and have traditionally been used to predict the risk of end-organ damage. Such measurements, however, do not reflect accurately the 24-h mean blood pressure and hourly variations. For any value of cuff blood pressure, a lower 24-h mean blood pressure was associated with a lower prevalence and severity of end-organ damage. In the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study, data from 24-h ambulatory blood pressure monitoring (ABPM) were more strongly associated with prognosis than other blood pressure data. Longitudinal evidence of the clinical relevance of 24-h ABPM data in predicting cardiovascular risk is less extensive. However, results from the Study on Ambulatory Monitoring of Pressure and Lisinopril Evaluation (SAMPLE) trial show the superiority of mean 24-h, daytime and night-time blood pressures over clinic readings in predicting the regression of left ventricular mass index in treated hypertensive patients. Furthermore, a direct, positive relationship has been established between 24-h blood pressure variability and the severity and rate of progression of end-organ damage. In addition, ABPM data demonstrate that hypertensive patients who do not exhibit a nocturnal reduction in blood pressure have a higher incidence of end-organ damage. Future directions for research and treatment of hypertension will need to consider the circadian cycle of blood pressure, the effect of treatment on blood pressure variability, and the magnitude of blood pressure changes in daily life.

Antihypertensive Agents↗

PubMed1990

[Effects of early biologic and psychosocial risk factors on mental performance and disease-promoting behavior of adult medical patients].

UNLABELLED: Early biological and social risks were related to measures of cognitive functioning and illness behaviour in adult patients. RESULTS: 1. Self-reported data on risks in early developmental stages are consistent with longitudinal data and theoretical assumptions. 2. Patients with biological risks show deficits in fluid abilities and signs of mild cerebral insufficiency. 3. Socially handicapped patients tend to coronary-prone behaviour and report more emotional strain while coping with complex problems.

Arousal↗

PubMed1996

Spondyloarthropathies in circumpolar populations: I. Design and methods of United States and Russian studies.

Parallel epidemiologic studies of spondyloarthropathy in aboriginal circumpolar populations were carried out by U.S. and Russian investigators. These complementary studies used the same data collection instrument and disease criteria to facilitate comparisons. During three expeditions to Siberia, Russian investigators collected cross-sectional data from four settlements of Eskimos and Chukchi Indians on the Chukotka peninsula for a study of disease prevalence. U.S. researchers collected cross-sectional data from Eskimos in four Alaskan regions for studies of prevalence and longitudinal data for studies of clinical manifestations, natural history, disease impact, and health care utilization. The aims of these studies were to describe the spectrum of spondyloarthropathy in these populations, and to lay the groundwork for investigations of the role of specific genetic and environmental factors in the pathogenesis and expression of disease. These studies were carried out with a minimum disruption to the native people.

Alaska↗

PubMed2001

Volunteer work and well-being.

Using two waves of panel data from Americans' Changing Lives (House 1995) (N = 2,681), we examine the relationships between volunteer work in the community and six aspects of personal well-being: happiness, life satisfaction, self-esteem, sense of control over life, physical health, and depression. Prior research has more often examined the effects of voluntary memberships than of volunteer work, has used cross-sectional rather than longitudinal data, and, when longitudinal, has emphasized social causation over selection effects. Focusing only on the consequences of volunteer work overlooks the antecedents of human agency. People with greater personality resources and better physical and mental health should be more likely to seek (or to be sought for) community service. Hence, we examine both selection and social causation effects. Results show that volunteer work indeed enhances all six aspects of well-being and, conversely, people who have greater well-being invest more hours in volunteer service. Given this, further understanding of self- versus social-selection processes seems an important next step. Do positive, healthy people actively seek out volunteer opportunities, or do organizations actively recruit individuals of these types (or both)? Explaining how positive consequences flow from volunteer service may offer a useful counterpoint to stress theory, which has focused primarily on negative life experiences and their sequelae.

Attitude to Health↗