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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↗
PubMed2004

A longitudinal genetic analysis of low verbal and nonverbal cognitive abilities in early childhood.

By middle childhood, the same genetic factors are largely responsible for individual differences in verbal and nonverbal abilities, suggesting a genetic basis for general cognitive ability ("g"). Our previous work on verbal and nonverbal abilities throughout the normal range of variation during infancy and early childhood suggests that genetic influences show domain-specific as well as domain-general effects, implying that the switch to nearly complete domain-general effects occurs later in development. Much less is known about the genetic structure of low cognitive performance, although our previous work has shown that a composite measure of low "g" is highly heritable at 2, 3 and 4 years of age. We report the first multivariate, longitudinal analyses of low verbal and nonverbal cognitive abilities (defined as the lowest 10% of the distribution) at 2, 3 and 4 years of age using data from 9026 pairs of UK twins assessed by their parents as part of the Twins Early Development Study (TEDS). Domain-general genetic influences increased significantly from 2 to 3 to 4 years. Although the phenotypic polychoric correlation between low verbal and low nonverbal ability was similar at 2, 3 and 4 years (.36,.43,.35), the genetic contribution to the phenotypic correlation increased dramatically (.37,.47,.76), with a corresponding decrease in the comorbid influence of shared environment (.61,.44,.35). We conclude that for low ability, as well as for normal variation in ability, genetic "g" emerges during early childhood but is not fully developed until middle childhood.

Child, Preschool↗
PubMed2004

Shifts in percentiles of growth during early childhood: analysis of longitudinal data from the California Child Health and Development Study.

OBJECTIVE: To document growth-velocity changes across major percentiles during the preschool years. DESIGN: Analyses of longitudinal data using height-for-age, weight-for-age, weight-for-height, and body mass index (BMI)-for-age percentiles were performed to examine crossing of major percentiles of the Centers for Disease Control and Prevention 2000 growth charts. The 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles were defined as the major percentiles. SETTING: Data from the California Child Health and Development Study were used. SUBJECTS: A total of 10,844 children up to 60 months of age, with 44,296 height and weight measurements, were included in our final analysis. RESULTS: For height-for-age, 32% of children between birth and 6 months of age, 13% to 15% of children between 6 and 24 months of age, and 2% to 10% of children between 24 and 60 months of age crossed 2 major percentiles. For weight-for-age, 39% of children between birth and 6 months of age, 6% to 15% of children between 6 and 24 months of age, and 1% to 5% of children between 24 and 60 months of age crossed 2 major percentiles. In contrast, for weight-for-height, 62% of children between birth and 6 months of age, 20% to 27% of children between 6 and 24 months of age, and 6% to 15% of children between 24 to 60 months of age crossed 2 major percentiles. Similar to the pattern observed for weight-for-height, 8% to 15% of children between 24 and 60 months of age crossed 2 major BMI-for-age percentiles. During the preschool years, weight-for-height had the highest percentages of children who crossed 2 major percentiles, and weight-for-age had the lowest percentages of children who crossed 2 major percentiles among these 3 indices. CONCLUSIONS: Shifts in growth rates were very common for children from birth to 6 months of age, somewhat less common for children 6 to 24 months of age, and least common for children 24 to 60 months of age. Shifts in weight-for-height occurred more frequently than did other growth changes. Pediatricians must consider the prevalence of growth rate shifts during infancy and early childhood before they counsel parents regarding growth or refer children for additional evaluations of growth.

Body Height↗
PubMed1992

Age-specific correlation analysis of longitudinal physical fitness levels in men.

This study investigated the age-specific tracking of adult health- and performance-related fitness scores. In addition, the independent contribution of adolescent physical characteristics to the explanation of adult fitness scores was also studied. The sample consisted of 173 adults observed at age 30 years. These subjects had been followed at annual intervals from age 13 to age 18 years and were remeasured at age 30 years. At each age nine fitness tests were administered together with the recording of anthropometric dimensions, biological maturation, sports participation and family characteristics. Tracking was measured by the inter-age correlations at each age between 13 and 18 years and the performance scores at 30 years. The independent contribution of characteristics observed during adolescence to the explanation of adult fitness was investigated through stepwise multiple regression analysis and discriminant analysis with the adult fitness scores as the dependent variables and the fitness, maturation, anthropometric characteristics, sports participation and family background as the independent variables. Tracking between age 13 and age 30 years was moderately high (46% of variance explained) for flexibility, low to moderate (between 19% and 27% of variance explained) for the other fitness parameters and low for pulse recovery and static strength (7% to 11% of variance explained). Between age 18 and age 30 years the tracking was high for flexibility, moderately high for explosive and static strength, and moderate for the other fitness parameters except for pulse recovery. The amount of variance of adult fitness levels explained increased significantly when other characteristics observed during adolescence entered the regressions or discriminant functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Simultaneous genetic analysis of longitudinal means and covariance structure in the simplex model using twin data.

A longitudinal model based on the simplex model is presented to analyze simultaneously means and covariance structure using univariate longitudinal twin data. The objective of the model is to decompose the mean trend into components which can be attributed to those genetic and environmental factors which give rise to phenotypic individual differences and a component of unknown constitution which does not involve individual differences. Illustrations are given using simulated data and repeatedly measured weight obtained in a sample of 82 female twin pairs on six occasions.

Analysis of Variance↗
PubMed1978

Pitfalls and problems in the interpretation of AFP data--myths and misuse of the "normal range".

Drawing a line more intelligently for AFP data means using as a denominator two fairly well-defined populations (abnormal and normal), instead of one ill-defined normal population. The line is drawn at the intersect between two curves to minimize the error of misclassification; this replaces an arbitrarily defined cutoff level (multiples of the standard deviation unit). Moving the line to the right reduces the false positive error when screening for NTD, whereas moving the line to the left provides a sensitive alert signal for routine screening of maternal sera by AFP determinations for fetal distress. Adjustment of the line for cost and benefit factors and the use of probability statements that include the prevalence of specific conditions all help sharpen medical classification and decisions. Cross-sectional analysis is separated from longitudinal analysis. A benefit from this discussion may be the replacement of the normal range with a simple plot of AFP results or a percentile distribution, which would be more meaningful and more easily understood by all.

Costs and Cost Analysis↗
PubMed2004

Particle image velocimetry for flow analysis in longitudinal planes across a mechanical artificial heart valve.

In the last decades a great number of in vitro studies have been conducted to improve the design and to understand the transvalvular flow patterns under steady-state and pulsating flow conditions. Steady-state tests are useful for studying the flow established upstream and downstream of the valve prosthesis in different flow conditions and, in particular, at the peak flow rate. In the present study, the particle image velocimetry (PIV) technique is employed to visualize the flow patterns in a precommercial model of a bi-leaflet mechanical heart valve prosthesis in a steady-state flow regime. The use of the PIV technique and a convenient test rig provide good conditions with which to investigate the whole flow field upstream and downstream of the valve. Velocity and vorticity maps are obtained for the flow passing through the prosthesis in different axial planes. A new and simple solution for the measurement test chamber is proposed. This innovative approach of observing the flow in staggered planes (other than diametrical planes) allows a flow analysis to be performed upstream and downstream of the valve in regions near the tube wall where it has the maximum potential for injury of the vessel's inner cell layer.

Blood Flow Velocity↗
PubMed2002

Changes in lean body mass and total body weight are weakly associated with physical functioning in patients with HIV infection.

CONTEXT: For clinicians managing weight loss in patients with HIV, it would be useful to understand how changes in lean body mass (LBM) effect physical functioning, and whether LBM is more strongly related to physical functioning than total body weight (TBW). OBJECTIVE: To determine the relationship of changes in LBM and changes in total body weight (TBW) to changes in self-reported physical functioning in men and women with HIV infection. METHODS: Study design was longitudinal analysis of 1474 patient-intervals (each interval was approximately 6 months long) in 486 persons. Patients were participants in Nutrition for Healthy Living, a cohort study of HIV positive persons in Massachusetts and Rhode Island. The main outcome measure was change in self-reported physical functioning. RESULTS: Of the 1,474 intervals, 1,165 were contributed by men and 309 by women. The mean CD4 count for the 1,474 intervals was 383 cells/ micro L. In men, 5 kg changes in LBM and TBW were associated with 2.2 (95% confidence interval, 0.9, 3.4, P= 0.001) and 2.6 (95% confidence interval, 1.3, 3.9, P= 0.0002) point changes in physical functioning (on a 100-point scale), respectively, after adjusting for covariates. The relationships of changes in LBM and TBW to changes in physical functioning were linear. In women, there were no significant relationships between changes in LBM or TBW to changes in physical functioning. CONCLUSIONS: In this longitudinal analysis of relatively healthy persons with HIV infection, changes in LBM and TBW were significantly related to changes in physical functioning in men, but the magnitude of the relationship was small. In women, changes in LBM and TBW were not related to changes in physical functioning. Our data suggest that it is not necessary to measure body composition (lean and fat compartments) to understand the impact of changes in weight on physical functioning - it is sufficient to follow total body weight.

Adult↗
PubMed2000

Selection of hepatitis B virus variants with aminoacid substitutions inside the core antigen during interferon-alpha therapy.

The hepatitis B virus (HBV) core antigen carries many epitopes relevant for B and T cell response that show aminoacid variation during viral infection. In a longitudinal analysis, sequential serum samples of 15 patients that suffered from chronic HBV infection were collected before, during, and after high-dose IFN-alpha treatment. The HBV preCore/Core (preC/C) sequence of the selected samples in each patient was determined and analysed for sequence variations compared to the pretreatment sample. The positions of HBV core aminoacid substitutions were assigned to immunodominant B, CD4(+) and CD8(+) cell epitopes. Seventy-five percent of all aminoacid substitutions were found within immunodominant T and B cell epitopes (12.5% were inside known HBV core mutation cluster regions) that show an increased number of clustered aminoacid substitutions during chronic HBV infection and overlap partially with the immunodominant epitopes. Only 12.5% of the detected core antigen aminoacid substitutions could not be assigned to any epitope or mutation cluster region. Stable HBV core antigen aminoacid substitutions, which were found between pretreatment sequence and the last sequence analysed during therapy, were found most frequently inside T helper cell epitopes. This longitudinal analysis of aminoacid substitutions inside the HBV core antigen in patients with chronic HBV infection shows that core aminoacid variations occur most frequently inside immunodominant HBV core epitopes, possibly due to an immuneselective pressure of the host against the virus. The data also suggest that stable HBV variants with aminoacid substitutions in immunodominant core epitopes can be selected during high-dose IFN-alpha therapy and persist after the end of treatment.

Adult↗
PubMed2005

Robust estimating functions and bias correction for longitudinal data analysis.

Robust methods are useful in making reliable statistical inferences when there are small deviations from the model assumptions. The widely used method of the generalized estimating equations can be "robustified" by replacing the standardized residuals with the M-residuals. If the Pearson residuals are assumed to be unbiased from zero, parameter estimators from the robust approach are asymptotically biased when error distributions are not symmetric. We propose a distribution-free method for correcting this bias. Our extensive numerical studies show that the proposed method can reduce the bias substantially. Examples are given for illustration.

Age Factors↗
PubMed2003

Serum levels of chemokines correlate with disease activity in patients with retinal vasculitis.

Retinal vasculitis (RV) is characterised pathologically by migration of leucocytes across the blood-retinal barrier leading to oedema and photoreceptor cell dysfunction. Chemokines are a family of small molecules involved in leucocyte migration. In this study, levels of chemokines were measured in serum from patients with RV and correlated with disease activity and drug treatment. Serum samples (n= 100; 25 active, 75 inactive) were obtained from 50 patients with RV, and levels of the chemokines MIP-1alpha, macrophage inflammatory protein-1beta (MIP-1beta) and monocyte chemoattractant protein-1 (MCP-1) were measured by ELISA. For longitudinal analysis levels of the same chemokines were measured in six consecutive serum samples from 10 of the above patients. Chemokine levels were correlated with disease activity and current drug treatment for each sample. Sera from 20 healthy individuals were used as control samples. Serum levels of MIP-1beta were significantly raised in patients with RV, whether active or not, compared to healthy controls (P= 0.04). Levels of MIP-1beta and MCP-1 correlated with disease activity in some patients and with prednisolone levels in patients on this treatment alone. MIP-1alpha levels were not detectable in all samples but were present in significantly more samples from patients with active or inactive RV compared with healthy controls. Serum levels of the chemokines MIP-1beta and MIP-1alpha, but not MCP-1 were raised in patients with retinal vasculitis. Longitudinal analysis suggested that MIP-1beta and MCP-1 levels were controlled by drug treatment, particularly prednisolone. These data demonstrate that chemokines are involved in the pathogenesis of RV and may act as novel therapeutic targets.

Chemokine CCL2↗
PubMed2006

Association of anti-mullerian hormone levels with obesity in late reproductive-age women.

OBJECTIVE: To describe anti-mullerian hormone (AMH) levels in healthy late reproductive age women and test the hypothesis that AMH levels are lower in obese compared to non-obese women. DESIGN: Cross-sectional study of AMH levels. Longitudinal analysis of a subgroup with 10 AMH measures over 8 years to support the cross-sectional results. SETTING: A population-based cohort of healthy late reproductive-age women. PARTICIPANTS: Selected from the cohort to provide comparisons of body mass index (BMI), menopausal status, age and race (n = 122). INTERVENTIONS: AMH levels were determined from blood samples collected in the parent study. MAIN OUTCOME MEASURE: Serum levels of AMH. RESULTS: AMH levels were 65% lower in obese women compared to non-obese women (0.016 ng/mL and 0.046 ng/mL, respectively). The geometric mean ratio was 0.35; 95% CI 0.13, 0.92, P=.034. AMH levels were significantly lower in the menopausal transition compared to premenopausal women and were significantly lower in all age groups > or =40 years compared to the 35-39 year-old women. BMI remained significantly associated with AMH levels in multivariable models that included adjustments for menopausal status, age, race and cycle day. In the longitudinal analysis of a subgroup, obese women had significantly lower mean AMH levels over the 8-year interval compared to the non-obese women (0.459 ng/mL; CI 0.28, 0.75 and 0.566 ng/mL; CI 0.34, 0.94, respectively; P=.016), corroborating the cross-sectional study results. CONCLUSIONS: Obese women have lower AMH levels compared to non-obese women in the late reproductive years. The findings offer further evidence of the complex relationships between obesity and reproductive hormone levels in women.

Age Factors↗
PubMed2006

Patterns of mean-level change in personality traits across the life course: a meta-analysis of longitudinal studies.

The present study used meta-analytic techniques (number of samples = 92) to determine the patterns of mean-level change in personality traits across the life course. Results showed that people increase in measures of social dominance (a facet of extraversion), conscientiousness, and emotional stability, especially in young adulthood (age 20 to 40). In contrast, people increase on measures of social vitality (a 2nd facet of extraversion) and openness in adolescence but then decrease in both of these domains in old age. Agreeableness changed only in old age. Of the 6 trait categories, 4 demonstrated significant change in middle and old age. Gender and attrition had minimal effects on change, whereas longer studies and studies based on younger cohorts showed greater change.

Follow-Up Studies↗
PubMedDate not supplied

Effects of age and gender but not prenatal cocaine on random ratio and delayed spatial alternation responding in rats.

This investigation employed a longitudinal analysis of rat operant behavior under two different schedules of reinforcement following prenatal exposure to cocaine. Offspring were derived from four maternal exposure groups: 50 mg/kg cocaine, their pair-fed controls, 25 mg/kg cocaine, and freely fed controls. Cocaine was administered via gavage from gestation day 6-20. A maternal fostering procedure was used. Pairs of male and female littermates were assigned to a 7-, 14-, or 21-month cohort and at the appropriate age were trained to respond on one lever in a two-lever operant chamber. Reinforcement was delivered with a series of random ratio (RR) schedules where the RR value was increased across sessions. After RR training, animals were examined with a delayed spatial alternation (DSA) procedure in the same chambers. Male offspring responded at higher rates than females during high-probability RR schedules, whereas advancing age was associated with lower response rates during low-probability RR schedules in both males and females. Prenatal cocaine exposure exerted only limited effects on RR responding during transition and did not affect DSA behavior. The results of this longitudinal analysis suggest that prenatal cocaine does not exert global or far-reaching learning deficits in prenatally exposed rats.

Aging↗
PubMed1992

Stepping through the drug use sequence: longitudinal scalogram analysis of initiation and regular use.

Using a new technique for tracing the sequence of use over time, this study examined the pattern of drug involvement among 4,145 West Coast adolescents over the 4-year span from Grades 7-10. During the period covered, the mid- to late 1980s, we found no evidence that cocaine has become a gateway drug. However, the data provided some support for treating cocaine initiation as a separate stage that precedes the onset of hard drugs other than pills. The analysis also showed that increased involvement with legal drugs constitutes an important step in the transition to hard drug use for most adolescents. Weekly alcohol use followed marijuana use and preceded use of all other illicit drugs for Hispanic, White, and Black youth. However, it followed use of hard drugs for Asians. Weekly smoking formed a distinct stage between initial use of pills and other hard drugs for non-Hispanic Whites. The results underscore the importance of prevention efforts aimed at curbing the transition to regular use of alcohol and cigarettes, as well as their initial use.

Adolescent↗
PubMed2005

Longitudinal cephalometric analysis after maxillary distraction osteogenesis.

The aim of this study was to analyze the long-term dentoskeletal changes in patients who received distraction osteogenesis of the maxilla. Seventeen patients aged 12 to 31 years underwent rigid external distraction osteogenesis for treatment of maxillary hypoplasia. Cephalograms were evaluated retrospectively regarding linear and angular measurements. Follow-up times ranged from 1 to 5 years. In two patients, there was no consolidation of the Le Fort I segment to the midface. After the 0- to 12-month period, the maxilla had a stable position in all patients. Nevertheless, there was further decrease of SNA and ANB and an increase of the facial concavity thereafter. Ongoing growth of the facial skeleton must be considered when distraction osteogenesis is chosen for the advancement of the maxilla in adolescents.

Adolescent↗
PubMed2001

Use of longitudinal data analysis in the determination of a global score for total hip replacement indication in osteoarthritis patients.

BACKGROUND: A composite index would help in medical practice for considering total hip replacement (THR) in hip osteoarthritis. In association with other parameters, such as age or general status, this index could serve to objectively determine the time to THR surgery, and might be used as an outcome measure in therapeutic trials. The objective of this study was to propose such an index, taking into account symptomatic, structural and therapeutic variables, and impact on lifestyle. METHODS: A curve-fitting procedure and a marginal model were used to highlight the average change in the variables over time. A discrete Cox model, with time-dependent covariates. was then performed to study the association between the variables and hip surgery, leading to the construction of a composite index. RESULTS: The smoothing and fitting analysis suggested takes into account not only the variables, but also the changes in their values during the preceding year, when studying the association between variables and hip surgery. Five covariates were retained in the Cox model, among them only one concerns the changes during the preceding year, showing that the values of the covariates are more important that their changes during the preceding year for THR indication. The coefficients of the model were transformed into new coefficients, so that their sum provided a severity score with individual values 0-100. DISCUSSION: Based on the values of reliable variables recorded during the four last visits, this score can be regarded as a valid index able to objectively help with THR indications. This score might also be used as an outcome measure in therapeutic trials.

Aged↗
PubMed1988

Longitudinal radiographic analysis of carious lesion progression.

Information on the rate at which carious lesions progress through the enamel of human teeth in an adult population was obtained from dental radiographs taken at 3-yr intervals, over a 10-yr period on 602 men. Clinical measures of calculus deposition, plaque accumulation, gingival inflammation, tooth mobility, periodontal pocket depth, and gingival recession were studied to find predictors that might be of value to the clinician for determining how frequently radiographs should be taken. We estimate that 50% of the enamel lesions on mesial and distal surfaces, if left untreated, would not progress into the dentin until 73 months had elapsed after the lesion was initiated. Significant differences in the progression rate were associated with the arch and tooth type. Patient age, number of decayed or filled surfaces, degree of gingival inflammation, amount of recession, and plaque accumulation were positively associated with more rapid caries progression, while greater numbers of teeth present were predictive of slower disease progression.

Adult↗