The analysis of longitudinal data in epidemiologic studies.
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Adolescent↗
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Analysis of longitudinal relaxation rate constants from magnetization transfer MR images of human tissues at 0.1 T.
The human calf muscle was examined by using the magnetization transfer MR imaging technique. The time-dependent saturation transfer (TDST) method was applied at low magnetic field 0.1 T in order to measure the mobile water relaxation time T1w, the magnetization transfer rate Rwm from water to solid macromolecules, and the magnetization transfer contrast (MTC) of the human tissue. The magnetization transfer contrast of 0.67 was attained. The transfer rate Rwm was 4.5 sec-1 (+/- 0.3 sec-1) for the anterior tibial muscle and 5.0 sec-1 (+/- 0.4 sec-1) for the gastrocnemius muscles. The values of Rwm are considerably larger than the values of corresponding relaxation rates measured at high fields. The relaxation rate measurements of human tissues in vivo was shown to be possible at 0.1 T even within the framework of normal routine MR imaging. Magnetization transfer MR imaging is a very promising and practical method in order to assess the relaxation processes in heterogeneous human tissues in vivo, and it can improve the tissue characterization possibilities of MR imaging techniques.
Humans↗
Heritability of craniometric and occlusal variables: a longitudinal sib analysis.
There has long been interest in the inheritance of malocclusion, but few studies have distinguished between skeletal (craniometric) variables and occlusal, tooth-based variables (e.g., anterior irregularity, rotations, displacements). This study was based on serial assessments of untreated persons in 30 sibships from 4 years (full deciduous dentition) to 20 years of age (full permanent dentition) in the Bolton-Brush Growth Studies of Ohio. Results define a clear dichotomy: craniometric variables (k = 29) typically show significant additive components of variance; correlations increase from age 4 to age 20; and correlations average 0.43 at adulthood. Tooth-based variables of position and relationship (k = 21) reach significance only occasionally; correlations decrease with age to the extent that few variables for subjects at age 20 have a correlation significantly different from zero. In contrast to craniometric variables, which have high heritabilities, almost all of the occlusal variability is acquired rather than inherited.
Adolescent↗
Perceived smoking norms, socioenvironmental factors, personal attitudes and adolescent smoking in China: a mediation analysis with longitudinal data.
PURPOSE: To gather information on inter-relationships among risk factors affecting adolescent smoking for tobacco control in China, the world's largest tobacco producer and consumer. METHOD: Longitudinal data were collected six months apart in 2003 from 813 students in grades 7, 8, 10, and 11 from two schools in Beijing, China. Linear regression was used to assess both the direct effect from predictor variables (smoking among influential others, pro-tobacco media, and attitudes toward smoking) on cigarette use and the indirect effect mediated through the perceived smoking norms (percentage of smokers among peers). RESULTS: Among the 803 subjects (mean age of 15.5 years, SD = 1.7; 52.1% female), 18.3% of males and 1.7% of females smoked in the past 30 days. Smoking among influential others (best friends, father, mother, male teachers, female teachers, and adults in general) and perceived positive psychological and social rewards from smoking at baseline were associated with number of cigarettes smoked at follow-up, whereas exposure to pro-tobacco media was not significantly associated with smoking. The mediated effect was greater for adult smoking (70% to 90%) than for best friend smoking (11% to 16%). CONCLUSION: Smoking among influential others and attitudes toward smoking influence adolescent smoking both directly and indirectly. The finding of the indirect effect mediated through perceived smoking norms expands our knowledge on smoking etiology. Effective adolescent smoking intervention programs in China need to include a component targeting adult smoking to reduce perceived smoking norms.
Adolescent↗
Predicting inadequate long-term lung development in children with congenital diaphragmatic hernia: an analysis of longitudinal changes in ventilation and perfusion.
PURPOSE: Infants born with congenital diaphragmatic hernia (CDH) demonstrate a wide variability in postnatal catch-up lung growth. The goals of this study were to assess the pulmonary development of children born with CDH using sequential ventilation-perfusion (V/Q) scintigraphy and to identify the perinatal factors that correspond to a progressive V/Q mismatch. METHODS: The records of 137 patients seen between 1990 and 2005 in a multidisciplinary CDH clinic were reviewed. Changes in the ipsilateral V/Q quotient were compared in 46 patients who had 2 or more studies with the following variables: sex, patch repair, laterality, gestational age, and use of extracorporeal membrane oxygenation. An abnormal V/Q quotient was defined as greater than 1.2 (reference range, 0.8-1.2). RESULTS: Abnormal V/Q scans were identified in 28 (61%) of the 46 patients at the time of the last V/Q study. Patients who underwent a patch repair had nearly 7 times the risk (P < .001) of developing an ipsilateral V/Q mismatch. The use of extracorporeal membrane oxygenation had a variable effect on the probability of an abnormal V/Q study finding. No other variable was significant. CONCLUSIONS: Many children with CDH develop significant and progressive V/Q mismatches. Although some perinatal variables appear to be predictive of this phenomenon, they may simply be surrogates for a greater degree of pulmonary hypoplasia present at birth. This subpopulation of CDH survivors is an identifiable group clearly at risk and thus requires long-term follow-up.
Adolescent↗
Quantitative genetic analysis of longitudinal trends in height: preliminary results from the Louisville Twin Study.
A preliminary series of quantitative genetic models was applied to a subset of longitudinal height data, spanning birth to maturity, gathered from twin families in the Louisville Twin Study. Descriptive Cholesky factor parameterization was found to give more satisfactory results than did a system of constraints based on a model of developmental transmission of a time-constant and time-specific factors. The results from application of two autosomal sex-limitation models are contrasted with those from a model specifying both autosomal and sex-chromosomal patterns of inheritance. The latter model was more conducive to parameter reduction. Although these models do not constitute conclusive tests of autosomal sex-limitation versus sex-linkage, the more parsimonious model is consistent with previous research suggesting a stature locus on the long arm of the Y chromosome. Heritability of height is estimated at about 90% or greater from 6 years of age on. Substantial and fairly constant longitudinal genetic correlations are found from 3 years of age on. Shared environmental effects unrelated to parental height were seen for birth length, corrected for gestational age, to height at 3 years of age, but these are not satisfactorily differentiated from possible twin effects in the present sample. The genetic consequences of assortative mating are emphasized since failure to take assortment into account can lead to overestimation of shared environmental effects and under-estimation of genetic effects. The results indicate that about 20% of within-gender variability for mature height can be attributed to the genetic consequences of assortment, even though the phenotypic marital correlation of 0.22 is quite modest. The importance of testing the assumption of multivariate normality underlying the application of the method of maximum-likelihood is also highlighted.
Body Height↗
Analysis of longitudinal bacterial carriage studies accounting for sensitivity of swabbing: an application to Neisseria meningitidis.
Longitudinal carriage studies of colonizing bacteria such as Neisseria meningitidis can provide important insights into the transmission dynamics of these organisms. Carriage is detected by culturing from a nasopharyngeal swab, but the sensitivity of this technique is low and varies between studies. This paper applies a statistical method for estimating the sensitivity of swabbing, infection rate, recovery rate and initial prevalence of carriage to three longitudinal carriage studies of N. meningitidis. These parameters and 95% confidence intervals were estimated using maximum likelihood techniques. The sensitivity of swabbing was estimated to be 60-83% and this should be taken into account when interpreting carriage studies. The estimates of force of infection and recovery rates seem to be consistent with estimates from more traditional methods. Differences in the parameter estimates between datasets may be due to differences in study design. This method could be used to assist in the design of future carriage studies.
Carrier State↗
Limited variations in 15N CSA magnitudes and orientations in ubiquitin are revealed by joint analysis of longitudinal and transverse NMR relaxation.
The site-specific magnitudes and orientations of the chemical shift tensors have been estimated for 70 backbone (15)N-nuclei in human ubiquitin from the field dependence of dynamic independent ratios between relaxation rates, both longitudinal and transverse, measured at 9.4, 11.7, 14.1, and 18.8 T. The results were jointly analyzed with previously published relaxation data [Fushman; Tjandra; Cowburn. J.Am. Chem. Soc. 1998, 120, 10947-10952] [Kover; Batta. J. Mag. Reson. 2001, 150, 137-146]. The effective magnitudes of the anisotropies distribute around 169 ppm with a variability of 5 ppm. The orientation factors, reflecting the orientation of the CSA relative to the NH bond, distribute around -0.80 with a variability of 0.04, which corresponds to an angle between the symmetry axis of an assumed axially symmetric shielding tensor and the NH bond of 21.4 degrees, and a variability of 2.3 degrees. Correlations with the isotropic (15)N-chemical shifts are observed. Variations in the shielding anisotropies add uncertainty to the obtained order parameters proportional to the square of the magnetic field, when data are analyzed using an assumed invariant CSA tensor for all sites. Around 3% additional uncertainty in the order parameters for 800 MHz data is expected. The optimal TROSY field for amide nitrogen TROSY is estimated, with only marginal variations due to site-to-site variations. Variations in the shielding tensors add uncertainty to the exchange terms calculated from cross-correlation rates. An approach for estimating the exchange terms is suggested, where the uncertainty due to CSA-variations is minimized.
Glycine↗
Longitudinal genetic analysis of EEG coherence in young twins.
During middle childhood, continuous changes occur in electroencephalogram (EEG) coherence, an index of cortico-cortical connectivity of the brain. In the gradual development of EEG coher ence, occasional "growth spurts" are observed which coincide with periods of discontinuous development in cognition. Discontinuous development may reflect changes in the genetic architecture of a trait over time, for instance, by the emergence of new genetic factors. To examine stability and change in genetic and environmental influences on EEG coherence from ages 5 to 7 years, intrahemispheric EEG coherences from 14 connections were collected twice in 209 twin pairs. Overall, heritabilities (h2) were moderate to high for all EEG coherences at both ages (average: 58%). For occipito-cortical connections in the right hemisphere, h2 increased with age due to a decrease in environmental variance. For prefronto-cortical connections in the left hemisphere, h2 decreased with age due to a decrease in genetic variance. New genetic factors at age 7 were found for prefronto-parietal coherence, and centro-occipital and parieto-occipital EEG coherences in both hemispheres and, in the left hemisphere, for prefronto-frontal EEG coherences. Mean genetic correlation for these cortico-cortical connections over time was 0.72, indicating that at least part of the genetic influences is age-specific. We argue that this is convincing evidence for the existence of stage-wise brain maturation from years 5 to 7, and that growth spurts in EEG coherence may be part of the biological basis for discontinuous cognitive development at that age range.
Brain Mapping↗
Stability and change in adult intelligence: 1. Analysis of longitudinal covariance structures.
We address two questions of central interest in adult intellectual development: the equivalence of psychometric tests' measurement properties at different ages, and the stability of individual differences in intelligence over time. We performed a series of longitudinal factor analyses using the LISREL program to model longitudinal data from Schaie's Seattle Longitudinal Study. The results indicate complete invariance in the loadings of five subtests of Thurstone's Primary Mental Abilities battery on a general intelligence factor. Individual differences in general intelligence were highly stable over 14-year epochs, with standardized factor correlations averaging about .9 between adjacent 7-year testing intervals. These results indicate that most individuals in this relatively select longitudinal sample maintained their relative ordering in intelligence.
Adult↗
Automatic analysis of longitudinal growth data on the Website willi-will-wachsen.de.
Many disorders of child development can only be treated successfully when they are detected early. Thus, child development should be checked periodically. Usually, a few parameters are sufficient to check whether or not a child is developing normally in terms of growth. By making such checks publicly available on the website: willi-will-wachsen.de the authors hope to provide a tool which helps the automatization of simple check procedures and thereby detect with less effort more children with growth disorders.
Adolescent↗
Analysis of longitudinal marginal structural models.
In this article we construct and study estimators of the causal effect of a time-dependent treatment on survival in longitudinal studies. We employ a particular marginal structural model (MSM), proposed by Robins (2000), and follow a general methodology for constructing estimating functions in censored data models. The inverse probability of treatment weighted (IPTW) estimator of Robins et al. (2000) is used as an initial estimator and forms the basis for an improved, one-step estimator that is consistent and asymptotically linear when the treatment mechanism is consistently estimated. We extend these methods to handle informative censoring. The proposed methodology is employed to estimate the causal effect of exercise on mortality in a longitudinal study of seniors in Sonoma County. A simulation study demonstrates the bias of naive estimators in the presence of time-dependent confounders and also shows the efficiency gain of the IPTW estimator, even in the absence such confounding. The efficiency gain of the improved, one-step estimator is demonstrated through simulation.
Aged↗
Exploratory analysis of longitudinal trials with staggered intervention times.
Longitudinal trials involving surgical interventions commonly have subject-specific intervention times, due to constraints on the availability of surgeons and operating theatres. Moreover, the intervention often effects a discontinuous change in the mean response. We propose a nonparametric estimator for the mean response profile of longitudinal data with staggered intervention times and a discontinuity at the times of intervention, as an exploratory tool to assist the formulation of a suitable parametric model. We use an adaptation of the standard generalized additive model algorithm for estimation, with smoothing constants chosen by a cross-validation criterion. We illustrate the method using longitudinal data from a trial to assess the effect of lung resection surgery in the treatment of emphysema patients.
Algorithms↗
Re: "Time-to-event analysis of longitudinal follow-up of a survey: choice of the time-scale".
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Age Factors↗
Age-specific correlation analysis of longitudinal blood pressure data.
To evaluate the predictive value of blood pressures for future levels, longitudinal measurements were analyzed among Welsh subjects from age 5 to 74 at entry. The measurements were taken on 863 individuals from the Vale of Glamorgan in 1956, 1960, 1964, and 1971 and on 734 individuals from the Rhondda Fach in 1954, 1958, 1964, and 1971. The tracking correlation, defined as the correlation between blood pressure readings on the same person taken at two different times, is used as a descriptive measure of the magnitude of the association. The tracking correlations range from 0.25 to 0.6-0.7 with most of the increases occurring before age 20. The tracking correlation depends on initial age, sex, and time interval between measurements. The age-specific tracking correlations decrease as time interval between measurements increases. For a given time interval, the age-specific correlations are slightly higher for females than for males. These findings are very similar for each of the two regions studied.
Adolescent↗
The use of residuals for longitudinal data analysis: the example of child growth.
Health impact evaluations often measure changes in health status over part of a total life experience. The effects on health up to and including the start of the evaluation, which are embodied in the measure of initial health status, need to be removed while examining the effects that other variables exert during the evaluation period on final health status. Statistical models, which include initial health status as a covariate while examining the effects of other variables during the evaluation, confound the effects of a determinant during evaluation with preevaluation effects, because they do not differentiate between effects produced at different times by the same determinant. A residual model removes the preevaluation effects by regressing final health status on initial health status. The residuals from this regression are then regressed on the other predictor variables. In this paper, standard covariate adjustment, which includes all effects simultaneously, is compared with a two-part residual model using child growth as an example. The simultaneous model over- and underpredicts growth relative to the residual model depending on the age and initial body size of a child. In general, whenever initial (preintervention) and final (postintervention) measures of health outcome exist, the residual model should be considered on the basis of biologic and epidemiologic consideration, not solely on statistical optimality.
Anthropometry↗
Progressive loss of pancreatic function in chronic pancreatitis is delayed by main pancreatic duct decompression. A longitudinal prospective analysis of the modified puestow procedure.
OBJECTIVE: This study evaluated the effect of operative drainage of the main pancreatic duct (MPD) on functional derangements associated with chronic pancreatitis (CP). SUMMARY BACKGROUND DATA: The author previously reported delayed functional impairment in an evaluation of the impact of operative drainage in patients with CP. The author now reports on a prospective study of 143 patients with this diagnosis. METHODS: Each patient underwent 1) ERCP, 2) the Bentiromide PABA, 3) 72-hour fecal fat test, 4) oral glucose tolerance test (OGTT) and 5) fat meal (LIPOMUL)--stimulated pancreatic polypeptide release (PP). All patients were stratified as mild/moderate (M/M) or severe CP on the basis of a 5-point system that was developed by the author. Patients were studied at 16-month intervals. RESULTS: All 143 patients underwent initial and follow-up evaluations in a mean follow-up of 47.3 months; 83 of 143 patients had M/M grade at initial evaluation. Eighty-seven patients underwent (MPD) decompression to relieve abdominal pain. In a separate prospective 17 patients with a diagnosis of CP, a grade of M/M and non-disabling abdominal pain were randomized to operative or non-operative treatment; 9 of these randomized patients were operated upon and 8 were not. No patient improved their grade during follow-up; 47 of 83 M/M patients had operative drainage and 36 did not. This grade was preserved in 41 of 47 (87%) operated patients but in only 8 of the 36 non-operated patients (22%). In the randomized trial, seven of nine operated patients retained their functional status in follow-up, whereas only two of eight patients (25%) randomized to non-operation preserved their functional grade. CONCLUSIONS: These data in this large study as well as among a previous randomized sample, support a policy of early operative drainage before the development of irreversible functional impairment in patients with chronic pancreatitis and associated dilation of the main pancreatic duct.
Adult↗
Morphological progression of emphysema on thin-section CT: Analysis of longitudinal change in the number and size of low-attenuation clusters.
OBJECTIVES: To evaluate morphological changes in the number and size of low-attenuation clusters on computed tomography (CT) in patients with emphysema. MATERIALS AND METHODS: In 27 patients who had follow-up CT scans for 6 months or greater, initial 27 scans and follow-up 39 scans were analyzed. The number per slice (LAN/s) and mean size (LAS) of low-attenuation clusters less than -950 HU, and total low-attenuation area below -950 HU per slice (LAA-950/s) were calculated. RESULTS: LAS and LAA-950/s were significantly increased over time. No significant correlation was found between LAN/s and follow-up period. LAS increased in 37 of 39 (95%) follow-up scans, whereas LAN/s decreased in 17 of 39 (44%) follow-up scans. CONCLUSIONS: On the morphological progression of emphysema, the mean size of low-attenuation clusters was significantly increased during the follow-up period, whereas no significant correlation was found between the number of low-attenuation clusters and follow-up period.
Aged↗