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PubMed2000

Liver function and hepatitis markers in carriers of hepatitis B virus in New Zealand.

AIMS: The Hepatitis Foundation has identified many chronic carriers of hepatitis B virus (HBV) in community surveys of schools and family contacts. This study reports the characteristics of carriers and the relationship between hepatitis markers and liver function. METHODS: Demographic data from confirmed chronic carriers of HBV in the North Island were correlated with liver function and hepatitis markers. Longitudinal data were obtained by following a cohort for two years with regular blood tests. RESULTS: Of 2778 confirmed carriers of HBV most were children or young adults and 56% were male. Sixty percent were Maori and 26% Pacific Island people. Loss of HBsAg occurred at less than 1% per year compared to 9% for HBeAg. Mean ages for 50% loss of HBeAg were 14 years for children of HBV negative mothers and 19 years for those of HBV carrier mothers. Fewer adult males than females were HBeAg positive. Alanine aminotransferase levels above 50 IU/L were found in 16% of HBeAg positive and 6% HBeAg negative cases. Other factors significantly associated with raised alanine aminotransferase were male gender (OR 1.8) and age more than 15 years (OR 2.0). Thirty five percent of HBeAg positive carriers with raised alanine aminotransferase levels spontaneously seroconverted to HBeAg negative in two years. However, raised alanine aminotransferase in HBeAg negative carriers was persistent in most cases and 38% had HBV-DNA detectable in serum. CONCLUSIONS: HBV carriage is less benign in adults than children, even after loss of HBeAg. It is recommended that all HBV carriers have regular checks of liver function. Those with persistent abnormality should be strongly advised to restrict alcohol and be assessed for possible antiviral treatment.

Adolescent↗

PubMed2004

Changes in children's exposure as a function of age and the relevance of age definitions for exposure and health risk assessment.

OBJECTIVE: The objective of this study was to review and synthesize the existing exposure information available to support the characterization and estimation of children's environmental health risks as a function of age. METHOD: This includes a review of the existing peer-reviewed literature and reports from the US Environmental Protection Agency (EPA) up through January 1, 2003 for information about exposure data for American children with a focus on identifying the age categories used and data gaps that limit our ability to estimate children's risks from exposure to environmental hazards. RESULTS: On the basis of this synthesis, several key data gaps emerge that suggest some areas in which exposure assessors may want to focus attention, including current breast milk consumption by infants and breastfeeding information for children over age 1 year; children's food-handling practices and how these lead to exposure (eg, by eating with dirty hands or by eating food that has dropped onto a contaminated surface); fish-intake rates for young children and for children whose families include sport fishers or whose families rely on self-caught fish for sustenance; incidental and intentional soil intake by children; soil adherence for dermal exposure; relationships between various microactivities, macroactivities, and microenvironments where children spend time; and a correlation between exposure factors and growth (ie, how children's exposure behaviors change over time). In contrast, relatively good exposure information exists for characterizing children's growth and water ingestion, and at least some exposure information exists for the wide ranges of exposures of regulatory interest. CONCLUSION: Given the currently available data, exposure assessors can estimate children's potential health risks from a number of different types of exposure, but longitudinal data are needed to reduce the significant uncertainties that arise from reliance on currently available data, and a number of dose-response challenges remain.

Aging↗

PubMedDate not supplied

Growth patterns and secular trends over four decades in the dynamics of height growth of Indian boys and girls in Sri Aurobindo Ashram: a cohort study.

BACKGROUND: Growth parameters are widely used in the assessment of health, nutrition and physical characteristics of a population; however, there still exist uncertainties regarding ethnic variation and the influence of physical activity on growth. Due to the paucity of longitudinal data, the dynamics of the adolescent growth spurt have not been satisfactorily examined in most populations. AIM: The main purpose of this longitudinal study is to present the secular trends in the dynamics of height growth over four decades. In the process, this paper also aims to establish current norms for some biological parameters of growth and to address issues concerning ethnic variation and the effect of childhood physical activity on growth. METHODOLOGY: Three hundred and one boys and 235 girls of Indian origin who had been enrolled in the Sri Aurobindo International Centre of Education (SAICE) by age 6 and remained for at least 3 uninterrupted years were divided into four birth cohort periods. Cross-sectional and longitudinal analyses were carried out to derive distance, velocity and acceleration curves. RESULTS: No significant differences were found between ethnic groups in any of the growth parameters. Over the 40-year span of this study, SAICE children prove to be taller than their Indian peers. A significant positive secular trend was seen in the height attained at all velocity turning points over the first two decades. Most pre-pubertal growth parameters in these children resemble those from developed nations. CONCLUSIONS: Children from most parts of India have similar genetic growth potential. After a significant positive secular trend in height attained over the first 20 years, the adult height has now plateaued. The significant difference in post-pubertal stature between the current generation and those of European origin indicates a genetic difference. Regular and graded physical activities have a salutary effect on growth. The data provide norms for healthy, active Indian child growing up in a satisfactory environment.

Adolescent↗

PubMed2002

Comparative longitudinal structural analyses of the growth and decline of multiple intellectual abilities over the life span.

Latent growth curve techniques and longitudinal data are used to examine predictions from the theory of fluid and crystallized intelligence (Gf-Gc theory; J. L. Horn & R. B. Cattell, 1966, 1967). The data examined are from a sample (N approximately 1,200) measured on the Woodcock-Johnson Psycho-Educational Battery-Revised (WJ-R). The longitudinal structural equation models used are based on latent growth models of age using two-occasion "accelerated" data (e.g., J. J. McArdle & R. Q. Bell, 2000; J. J. McArdle & R. W. Woodcock, 1997). Nonlinear mixed-effects growth models based on a dual exponential rate yield a reasonable fit to all life span cognitive data. These results suggest that most broad cognitive functions fit a generalized curve that rises and falls. Novel multilevel models directly comparing growth curves show that broad fluid reasoning (Gf) and acculturated crystallized knowledge (Gc) have different growth patterns. In all comparisons, any model of cognitive age changes with only a single g factor yields an overly simplistic view of growth and change over age.

Adult↗

PubMed1999

Natural history of amblyopia untreated owing to lack of compliance.

AIMS: A prospective study of the efficacy of amblyopia treatment in preschool children has recently been called for, requiring an untreated control group. The present study assessed data from patients with amblyopia untreated owing to lack of compliance, or with amblyopia risk factors, to determine outcome. METHODS: Longitudinal data were obtained from 18 4-6 year old patients who had initially been screened for amblyopia, strabismus, and/or bilateral refractive error, failed to comply with prescribed treatment, and in whom amblyopia was detected at a rescreening approximately a year later. The data from three previous studies comparing outcome of patients compliant and non-compliant with amblyopia treatment were also reanalysed. RESULTS: One child of the 18, who wore glasses sporadically, showed some improvement in visual acuity in the amblyopic eye. Otherwise, no child showed an improvement, and seven of the 17 (41%) for whom visual acuities were available at both screenings showed a deterioration of visual acuity in the amblyopic eye, including three who apparently developed amblyopia for the first time. A child with an ametropic risk factor for amblyopia whose visual acuity was not obtained at the first screening and who was largely non-compliant presented with amblyopia at the second screening. The reanalysed data from the three previous studies demonstrated a significantly poorer visual acuity outcome in the amblyopic eye in the non-compliant patient groups than in the compliant groups in each study. CONCLUSION: Preschool children with amblyopia or its risk factors are at risk of having the current amblyopia deteriorate, or of developing amblyopia, if not treated. These results raise questions about the ethical acceptability of a prospective study of amblyopia treatment at these ages.

Amblyopia↗

PubMed2005

Influence of prior sexual risk experience on response to intervention targeting multiple risk behaviors among adolescents.

PURPOSE: To identify correlates of sexual risk variations among African-American adolescents, and to examine the influence of prior sexual experience on response to a HIV risk-reduction intervention. METHODS: Eight hundred seventeen African-American youth aged 13 to 16 years living in and around urban public housing in Baltimore were recruited to participate in a HIV risk-reduction intervention targeting multiple risk behaviors. An instrument designed to measure three levels of sexual risk ("abstinent," "protected sex" [having sex with a condom], and "unprotected sex" [having sex without a condom]) was administered at baseline, 6 months and 12 months postintervention. Multiple regression analyses were conducted to identify predictors of the degree of sexual risk using longitudinal data. Repeated measure analyses were conducted to assess behavioral changes over time among the three groups. RESULTS: Data confirmed the co-variation of sexual risk behavior and other problem behaviors among adolescents, cross-sectionally and longitudinally. After exposure to an 8-session risk-reduction intervention, youth engaging in the highest degree of sexual risk demonstrated the greatest reduction in both sexual risk and other risks. These improvements were seen at both 6 months and 12 months postintervention. Youth who were abstinent at baseline maintained the lowest levels in risk involvement throughout the study period when compared with sexually active youth. However, abstinent youth risk involvement significantly increased at 6 months and 12 months after baseline. Youth engaging in protected sex at baseline demonstrated a significant increase in non-condom use and a significant decrease in multiple risk involvement over time. CONCLUSIONS: Results support HIV risk-reduction intervention efforts that target multiple risk behaviors. Response of adolescents to the intervention is directly related to the sexual risk behavior at baseline. These data may suggest that the response to risk behavior intervention depends in part on the risk behavior profile of the population to which it is being applied.

Adolescent↗

PubMed2002

Long-term and resegmentation precision of quantitative cartilage MR imaging (qMRI).

OBJECTIVE: Follow up of osteoarthritis (OA) and evaluation of structure modifying OA drugs require longitudinal data on cartilage structure. The aim of this study was to analyse the long term and resegmentation precision of quantitative cartilage analysis with magnetic resonance imaging (qMRI) in vivo, and to relate precision errors to the estimated cartilage loss in OA. METHOD: Sagittal MR images of the knee were obtained in 14 individuals, four datasets being acquired in a first imaging session. In 12 subjects, two further datasets were acquired over the next months. Image analysis was performed in the same session for image data obtained under short-term and long-term imaging conditions, and in three different sessions (months apart) for the first data set (resegmentation precision). RESULTS: Long-term precision errors ranged from 1.4% (total knee) to 3.9% (total femur) for cartilage volume and thickness and were only marginally higher than those under short term conditions. In the medial tibia, the error was 84 mm(3) compared with an estimated loss of >1,200 mm(3) in varus OA. Precision errors for resegmentation were somewhat higher, but considerably smaller than the intersubject variability. CONCLUSIONS: Scanner drift and changes in imaging or patient conditions appear not to represent a critical problem in quantitative cartilage analysis with magnetic resonance imaging (qMRI). In longitudinal studies, image analysis of sequential data should be performed within the same post-processing session. Under these conditions, qMRI promises to be a very powerful method to assess structural change of cartilage in OA.

Adult↗

PubMed2003

A Bayesian semiparametric joint hierarchical model for longitudinal and survival data.

This article proposes a new semiparametric Bayesian hierarchical model for the joint modeling of longitudinal and survival data. We relax the distributional assumptions for the longitudinal model using Dirichlet process priors on the parameters defining the longitudinal model. The resulting posterior distribution of the longitudinal parameters is free of parametric constraints, resulting in more robust estimates. This type of approach is becoming increasingly essential in many applications, such as HIV and cancer vaccine trials, where patients' responses are highly diverse and may not be easily modeled with known distributions. An example will be presented from a clinical trial of a cancer vaccine where the survival outcome is time to recurrence of a tumor. Immunologic measures believed to be predictive of tumor recurrence were taken repeatedly during follow-up. We will present an analysis of this data using our new semiparametric Bayesian hierarchical joint modeling methodology to determine the association of these longitudinal immunologic measures with time to tumor recurrence.

Bayes Theorem↗

PubMed2006

Causal analysis of case-control data.

In a series of papers, Robins and colleagues describe inverse probability of treatment weighted (IPTW) estimation in marginal structural models (MSMs), a method of causal analysis of longitudinal data based on counterfactual principles. This family of statistical techniques is similar in concept to weighting of survey data, except that the weights are estimated using study data rather than defined so as to reflect sampling design and post-stratification to an external population. Several decades ago Miettinen described an elementary method of causal analysis of case-control data based on indirect standardization. In this paper we extend the Miettinen approach using ideas closely related to IPTW estimation in MSMs. The technique is illustrated using data from a case-control study of oral contraceptives and myocardial infarction.

Journal Article↗

PubMed2006

Growth of the cornea from infancy to adolescence.

The intraocular distance and iris diameter of children and young adolescents were measured, with the aid of a measuring microscope, from photographs of their faces. True intraocular distance was measured with an intraocular caliper at the same time that the photographs were taken. These data were then compiled and horizontal visible iris diameters (HVIDs) were calculated. An equation was derived from the optics of the Gullstrand model eye to calculate horizontal corneal diameter (HCD) from HVID. Comparisons of HVIDs revealed no significant correlation with age in either a regression plot of cross-sectional data for subjects aged 1 month to 1 year, or all subjects whose ages ranged from 1 month to adolescence. Additional longitudinal data for 13 individuals, who had been photographed as both an infant (mean = 3.4 months) and as an older child or adolescent (mean = 8.6 years), were then compiled and HVIDs for these subjects at two different ages were compared. A Wilcoxon signed rank test revealed a small but significant amount of growth, 0.318 mm (p-value = 0.013), in the HVIDs over a mean age difference of 8.3 years for individuals measured twice during their lifetimes. The regression equation for this growth was: HVID = 10.52 (+/-0.095 S.E.) + 0.0305 (+/-0.014) x Age (years). From a comparison of data from earlier literature and our own measurements, we conclude that, after birth, the fastest growth of the cornea must occur during the first few months of life.

Adolescent↗

PubMed2003

Is knee radiography useful for studying the efficacy of a disease-modifying osteoarthritis drug in humans?

Recent research on the radiographic imaging of knee OA has helped clarify the features of imaging protocols that contribute to accurate representation of disease severity--specifically, the thickness of articular cartilage--and to sensitive detection of disease progression. The absence of standards for reproducible positioning of the knee in the conventional standing AP view obscures the true rate and variability of JSN in knee OA. Moreover, the standing AP view is susceptible to systematic bias insofar as longitudinal changes in knee pain might lead to over- or underestimation of radiographic JSW depending on the direction of change in pain. More recent protocols for standardized knee radiography have been designed to achieve reproducible alignment of the medical tibial plateau and x-ray beam. As a group these protocols permit measurement of tibiofemoral JSW with remarkable precision--the sine qua non of sensitivity to change--however, only limited longitudinal data is available to permit a direct evaluation of the suitability of these protocols for use in clinical DMOAD trials. Longitudinal studies published to date suggest that fluoroscopic positioning methods are superior to nonfluoroscopic methods with respect to reproducing the position of the knee in serial examinations performed several years apart. Fluoroscopic methods also appear to be superior with respect to achieving parallel alignment of the medial tibial plateau and x-ray beam in serial radiographs, a positioning marker strongly associated with sensitive detection of JSN in knee OA. It is important to note that while the various standardization protocols described in this article perform with great success in short-term demonstrations of the reproducibility of positioning and radiographic JSW, differences clearly exist between protocols in the quality of performance over intervals relevant to clinical DMOAD trials. Over intervals of 2 to 3 years, changes in patient characteristics (e.g., severity of knee pain, body weight, load bearing, varus--valgus deformity) and uncontrollable events related to radiography (e.g., technologist turnover, equipment upgrades) have ample opportunity to affect the technical quality of a radiological knee examination. It is difficult, therefore, to conclude whether or not an apparent difference with respect to sensitivity to OA progression between specific radiographic protocols, implemented in separate locations with different cohorts, reflects a robust difference in technical quality or uncontrollable patient variables and events. The most informative recent studies have provided the results of head-to-head longitudinal comparisons of alternative standardization protocols or conventional examination methods performed concurrently in the same subjects [20,22]. Additional comparative studies of this nature are needed, however, to fully characterize the strengths and weaknesses of currently available alternatives in a way that will permit generalizable conclusions regarding the best radiographic methods for multicenter DMOAD trials.

Biomechanical Phenomena↗

PubMed2004

Epidemiology of candidemia in Swiss tertiary care hospitals: secular trends, 1991-2000.

Candida species are among the most common bloodstream pathogens in the United States, where the emergence of azole-resistant Candida glabrata and Candida krusei are major concerns. Recent comprehensive longitudinal data from Europe are lacking. We conducted a nationwide survey of candidemia during 1991-2000 in 17 university and university-affiliated hospitals representing 79% of all tertiary care hospital beds in Switzerland. The number of transplantations and bloodstream infections increased significantly (P<.001). A total of 1137 episodes of candidemia were observed: Candida species ranked seventh among etiologic agents (2.9% of all bloodstream isolates). The incidence of candidemia was stable over a 10-year period. C. albicans remained the predominant Candida species recovered (66%), followed by C. glabrata (15%). Candida tropicalis emerged (9%), the incidence of Candida parapsilosis decreased (1%), and recovery of C. krusei remained rare (2%). Fluconazole consumption increased significantly (P<.001). Despite increasing high-risk activities, the incidence of candidemia remained unchanged, and no shift to resistant species occurred.

Antifungal Agents↗

PubMed2005

Inadequate sleep as a risk factor for obesity: analyses of the NHANES I.

STUDY OBJECTIVES: Sleep deprivation has been hypothesized to contribute toward obesity by decreasing leptin, increasing ghrelin, and compromising insulin sensitivity. This study examines cross-sectional and longitudinal data from a large United States sample to determine whether sleep duration is associated with obesity and weight gain. DESIGN: Longitudinal analyses of the 1982-1984, 1987, and 1992 NHANES I Followup Studies and cross-sectional analysis of the 1982-1984 study. SETTING: Probability sample of the civilian noninstitutionalized population of the United States. PARTICIPANTS: Sample sizes of 9,588 for the cross-sectional analyses, 8,073 for the 1987, and 6,981 for the 1992 longitudinal analyses. MEASUREMENTS AND RESULTS: Measured weight in 1982-1984 and self-reported weights in 1987 and 1992. Subjects between the ages of 32 and 49 years with self-reported sleep durations at baseline less than 7 hours had higher average body mass indexes and were more likely to be obese than subjects with sleep durations of 7 hours. Sleep durations over 7 hours were not consistently associated with either an increased or decreased likelihood of obesity in the cross-sectional and longitudinal results. Each additional hour of sleep at baseline was negatively associated with change in body mass index over the follow-up period, but this association was small and statistically insignificant. CONCLUSIONS: These findings support the hypothesis that sleep duration is associated with obesity in a large longitudinally monitored United States sample. These observations support earlier experimental sleep studies and provide a basis for future studies on weight control interventions that increase the quantity and quality of sleep.

Adult↗

PubMed2005

Longitudinal volumetric MRI change and rate of cognitive decline.

OBJECTIVE: To examine how baseline and change of volumetric MRI relate to cognitive decline in older individuals. BACKGROUND: Memory is associated with hippocampal integrity, whereas executive function has been linked to impaired frontal lobe function. Previous studies have shown that hippocampal and cortical atrophy are more strongly related to cognition than are measures of subcortical cerebrovascular disease (CVD). The authors hypothesized that memory (MEM) decline would be related to change in hippocampal volume (HC), whereas decline in executive function (EXEC) would be related to change of cortical gray matter volume (CGM) and measures of subcortical CVD. METHODS: Subjects from a multicenter study (n = 103) included cognitively normal, mildly impaired, and demented cases with and without subcortical lacunes. All had longitudinal cognitive evaluation (mean = 4.8 years) and two or more MRI scans at least one year apart (mean = 3.4 years). MRI measures included HC, CGM, total lacune volume (LAC), and white matter hyperintensity volume (WMH). Random effects modeling of longitudinal data assessed effects of MRI baseline and MRI change on baseline and change of psychometrically matched measures of MEM and EXEC. RESULTS: Change in MEM was related to HC baseline and HC change. Change in EXEC was related to baseline CGM and to change in CGM, HC, and LAC. Results were unchanged when demented cases were excluded. WMH was not associated with change in MEM or EXEC independent of HC, CGM, and LAC. CONCLUSION: Hippocampal volume was the primary determinant of memory decline, whereas executive function (EXEC) decline was related to multiple brain components. Results support a hypothesis that MEM decline is strongly influenced by Alzheimer disease (AD), whereas EXEC decline may be complexly determined by cerebrovascular disease and AD.

Aged↗

PubMed2002

Recruitment and attrition in twin register studies of childhood behavior: the example of the Australian Twin ADHD Project.

There are a growing number of large-scale initiatives for twin registers of children. The Australian Twin ADHD Project (ATAP) is used to illustrate two key limitations which may arise with such studies, namely (1) the importance of including or possibly excluding families in which one or both twins have significant developmental disability, and (2) the selective failure to recruit and/or the selective attrition of families in which parents and children share behavioral difficulties. Initially ATAP excluded 1 in 6 of families whose twins were enrolled in the volunteer-based Australian Twin Registry (ATR), and as more children with significant problems were identified, these families were sequentially excluded. With longitudinal data over ten years, two points about retention were identified: the difficulty of retaining the twins in late adolescence, and the loss of the families whose twins had more ADHD symptoms. We discuss strategies for limiting the loss of families and for ensuring comparability of data across registers with similar interests but different methods of recruitment and exclusion.

Adolescent↗

PubMed2002

Functional data analysis with application to periodically stimulated foetal heart rate data. II: functional logistic regression.

We present a basis solution for the modelling of a binary response with a functional covariate plus any number of scalar covariates. This can be thought of as singular longitudinal data analysis as there are more measurements on the functional covariate than subjects in the study. The maximum likelihood parameter estimates are found using a basis expansion and a modified Fisher scoring algorithm. This technique has been extended to model a functional covariate with a repeated stimulus. We used periodically stimulated foetal heart rate tracings to predict the probability of a high risk birth outcome. It was found that these tracings could predict 94.1 per cent of the high risk pregnancies and without the stimulus, the heart rates were no more predictive than chance.

Adult↗

PubMed1995

Interpreting quality improvement data with time-series analyses.

In quality improvement efforts, the data are frequently a series of measurements taken over time. A collection of statistical methods, commonly referred to as time-series analysis, provides a simple and understandable method for interpreting this longitudinal data. In this article, we present a time-series analysis of data on the quality of prenatal care at a mid-sized public hospital. We will demonstrate some simple tests that alert us to the potential value of using more sophisticated tests of association such as regression. Using regression, we show how to confirm a visual impression of an improvement. The analytical approach we present here is useful with many types of process or outcome data from health care quality improvement efforts.

Data Collection↗

PubMed1998

Variability in urinary flow rate and prostate volume: an investigation using the placebo arm of a drug trial.

PURPOSE: We analyzed a large data set to study reproducibility of peak urinary flow rates and prostate volumes in benign prostatic hyperplasia patients. MATERIALS AND METHODS: Longitudinal data were analyzed from 284 placebo treated patients in a double-blind, placebo controlled benign prostatic hyperplasia drug trial. RESULTS: A statistically significant increase in mean maximum flow rate was seen in the initial 3 measurements, as well as after adjusting for voided volume and time between uroflows. The mean maximum flow rate increased from 8.61 to 9.36 ml. per second at measurement 4 (8.7%). Of the patients 43% had 2 consecutive prostate volume determinations within +/- 10%. Within patient variability accounted for 7% of total prostate volume variability. CONCLUSIONS: With subsequent voidings maximum flow rate increases in a large group of patients. At least 4 uroflows must be performed to reach a plateau for maximum flow rate. Explanations for this finding may be the increasing experience of the patient and regression to the mean. These findings may impact on comparison of large trials of treatment efficacy. Within patient variability of prostate volume is substantial and, in addition to measurement method and lack of reader blinding to time and patient identity, may be caused by other yet unknown factors.

Aged↗