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PubMed2006

Characterizing the course of low back pain: a latent class analysis.

Understanding the course of back pain is important for clinicians and researchers, but analyses of longitudinal data from multiple time points are lacking. A prospective cohort study of consecutive back pain consulters from five general practices in the United Kingdom was carried out between 2001 and 2003 to identify groups defined by their pain pathways. Patients were sent monthly questionnaires for a year. Longitudinal latent class analysis was performed by using pain intensity scores for 342 consulters. Analysis yielded four clusters representing different pathways of back pain. Cluster 1 ("persistent mild"; n = 122) patients had stable, low levels of pain. Patients in cluster 2 ("recovering"; n = 104) started with mild pain, progressing quickly to no pain. Cluster 3 ("severe chronic"; n = 71) patients had permanently high pain. For patients in cluster 4 ("fluctuating"; n = 45), pain varied between mild and high levels. Distinctive patterns for each cluster were maintained throughout follow-up. Clusters showed statistically significant differences in disability, psychological status, and work absence (p < 0.001). This is the first time, to the authors' knowledge, that latent class analysis has been applied to longitudinal data on back pain patients. Identification of four distinct groups of patients improves understanding of the course of back pain and may provide a basis of classification for intervention.

Adult↗
PubMed2001

Longitudinal predictors of behavioural adjustment in pre-adolescent children.

OBJECTIVES: Longitudinal data from infancy onwards, from the Australian Temperament Project, a prospective study of the temperament and development of a large and representative sample of Victorian children, were examined to identify predictors of psychological disorder at 11-12 years of age. METHOD: Those children scoring in the at-risk range for psychological disorder according to parents, teachers and self-reports using the Child Behaviour Questionnaire were selected at 11-12 years of age for in-depth assessment and comparison with a group of children with no history of adjustment problems. Analyses of group differences using longitudinal data gathered from infancy to 12 years focused on parent and teacher reports on child temperament and behaviour, and various facets of home and school adjustment. RESULTS: The strongest predictors of adjustment at 12 years were previous behaviour problems, along with some specific temperament factors involving self-regulation capacities and mother's overall rating of child difficulty. Results based on parallel teacher data including peer adjustment, and social and academic competence measures were consistent with parent data. CONCLUSIONS: Our research confirms the persistence of early appearing behaviour problems in a community sample and the longitudinal influence of temperament factors in childhood. The study supports the need for a focus on early intervention and prevention strategies in the child mental health field.

Adolescent↗
PubMed2004

Early television exposure and subsequent attentional problems in children.

OBJECTIVE: Cross-sectional research has suggested that television viewing may be associated with decreased attention spans in children. However, longitudinal data of early television exposure and subsequent attentional problems have been lacking. The objective of this study was to test the hypothesis that early television exposure (at ages 1 and 3) is associated with attentional problems at age 7. METHODS: We used the National Longitudinal Survey of Youth, a representative longitudinal data set. Our main outcome was the hyperactivity subscale of the Behavioral Problems Index determined on all participants at age 7. Children who were > or = 1.2 standard deviations above the mean were classified as having attentional problems. Our main predictor was hours of television watched daily at ages 1 and 3 years. RESULTS: Data were available for 1278 children at age 1 and 1345 children at age 3. Ten percent of children had attentional problems at age 7. In a logistic regression model, hours of television viewed per day at both ages 1 and 3 was associated with attentional problems at age 7 (1.09 [1.03-1.15] and 1.09 [1.02-1.16]), respectively. CONCLUSIONS: Early television exposure is associated with attentional problems at age 7. Efforts to limit television viewing in early childhood may be warranted, and additional research is needed.

Analysis of Variance↗
PubMed2003

Does early physical activity predict body fat change throughout childhood?

BACKGROUND: Declining levels of physical activity in the population at large may be responsible in part for the rising rates of childhood obesity. Studies to date, however, have not consistently demonstrated such a protective effect. We used longitudinal data from the Framingham Children's Study (FCS) to address this important question. METHODS: We used 8 years of activity monitoring (Caltrac electronic motion sensors) and repeated anthropometry measures for 103 children to examine the effect of activity on body fat change from preschool to early adolescence. Longitudinal data analysis methods were employed to account for the use of repeated measures on these children. RESULTS: Children in the highest tertile of average daily activity from ages 4 to 11 years had consistently smaller gains in BMI, triceps, and sum of five skinfolds throughout childhood. By early adolescence (age 11), the sum of five skinfolds was 95.1, 94.5, and 74.1 for the low, middle, and high tertiles of activity, respectively (P for trend = 0.045). This protective effect of activity was evident for both girls and boys. CONCLUSION: This longitudinal study adds strong support for the hypothesis that higher levels of physical activity during childhood lead to the acquisition of less body fat by the time of early adolescence.

Adipose Tissue↗
PubMedDate not supplied

Focal nodular hyperplasia: natural course observed with CT and MRI.

PURPOSE: The purpose of this work was to assess the natural course of biopsy-proven focal nodular hyperplasia (FNH). METHOD: Eighteen biopsy-proven FNHs in 14 patients (12 women and 2 men) who were followed for at least 6 months with CT and/or MRI were included in the study. The volume of the lesions was calculated twice by two observers using the summation of areas method. Intra- and interobserver variability was assessed by intraclass correlation coefficients. Longitudinal data analysis was performed with generalized estimating equations. RESULTS: The volume of FNH was stable in 6 cases, decreased in 10 cases, and increased in 2 cases. Intra- and interobserver variability in size measurements was 5-10%. Intraclass correlation coefficients were >0.992. Longitudinal data analysis showed that there was a general trend of lesion regression. CONCLUSION: Long-term follow-up and objective measurements performed in patients with biopsy-proven lesions show that the natural course of FNH is variable. In particular, lesion regression is not rare.

Adolescent↗
PubMed1993

Do falls predict institutionalization in older persons? An analysis of data from the Longitudinal Study of Aging.

Data from the Longitudinal Study of Aging (LSOA) were analyzed to estimate the subsequent risk of institutionalization associated with a report of one or more falls, and to determine if the association is affected by controlling for demographic traits, chronic conditions, and disabilities present at baseline. Risk was estimated at two time points, 2 years and 4 years after baseline interview. A report of multiple falls at baseline was associated with an increased risk of institutionalization at both 2 years (odds ratio [OR] 3.1; 1.9-5.3) and 4 years (OR 2.6; 1.6-4.4) of follow-up. The risk was decreased but remained significant in a model controlling for age, sex, marital status, and selected chronic conditions associated with both report of falls and institutionalization. However, multiple falls were not significantly associated with institutionalization when measures of disability (number of difficulties with activities of daily living) were added to the model. These analyses suggest that multiple falls should be regarded as an important sentinel event to alert caregivers to the presence of underlying disease and disability that may require intervention.

Accidental Falls↗
PubMed2005

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↗
PubMed1985

Implementation of Rao's one-sample polynomial growth curve model using SAS.

Longitudinal data are frequently treated with the classic analysis of variance and regression models. However, these models assume independence of observations. Hoel (1964) demonstrated that the use of least-squares methods on intercorrelated serial observations results in the rejection of the null hypothesis much too frequently. Although appropriate models for analyzing longitudinal data have been available for quite some time, they have remained inaccessible due to cumbersome matrix manipulations. We implement Rao's (1959) one-sample polynomial growth curve model using the programming capability and matrix language of SAS, which involves testing the goodness-of-fit and calculation of confidence bands for polynomial growth curves fit to data at equally spaced time points. Confidence intervals for the parameters themselves are also computed. The method and program (presented in the Appendix) are illustrated with examples involving mandibular ramus height in 12 young male rhesus monkeys. The data set, which spans a 4 year period (yearly observations), is fit adequately by a quadratic equation. The data spanning a 2 year period (half-year observations) are fit adequately by the linear equation. These examples illustrate the considerable widening of confidence bands that occurs when polynomial equations having more terms than are needed to meet the goodness-of-fit requirement are considered.

Analysis of Variance↗
PubMed2004

The Dialysis Outcomes and Practice Patterns Study (DOPPS): design, data elements, and methodology.

The Dialysis Outcomes and Practice Patterns Study (DOPPS) is a prospective, observational study designed to elucidate aspects of hemodialysis practice that are associated with the best outcomes for hemodialysis patients. In DOPPS I, 308 hemodialysis units from 7 countries participated, including 145 facilities from the United States (1996-2001), 62 facilities from Japan (1999-2001), and 101 facilities from France, Germany, Italy, Spain, and the United Kingdom (all 1998-2000). DOPPS II (2002-2004) has included 320 hemodialysis units and more than 12,400 hemodialysis patients from the 7 DOPPS I countries as well as Australia, Belgium, Canada, New Zealand, and Sweden. Dialysis units are chosen via a stratified random selection procedure to provide proportional sampling by region and type of facility within each country. In DOPPS I and II, longitudinal data have been collected from both a prevalent (cross-sectional) patient sample and an incident patient sample. Data have also been collected on numerous facility practice patterns. Most DOPPS analyses incorporate both facility- and patient-level data in regression-based analyses to investigate predictors of survival, hospitalization, quality of life, vascular access type, and other outcomes. DOPPS longitudinal data also help identify trends in subject characteristics, practice indicators, medication use, and outcomes. The DOPPS remains a unique source of data on hemodialysis patients and facilities. It continues to refine its methods of data collection and analysis with the goal of improving hemodialysis practice and end-stage renal disease patient lives worldwide.

Humans↗
PubMed1979

Perinatal mortality by birth order within cohorts based on sibship size.

Cross-sectional surveys of perinatal mortality show a U-shaped curve when plotted against parity, implying that fourth and subsequent babies are at increased risk. Our study of a large, population-based longitudinal data set shows that this result is an artefact and that perinatal mortality falls with increasing parity. Within cohorts of mothers based on attained sibship size the perinatal mortality decreases with increasing parity and increases with sibship size. These associations, which are not noticeably affected by maternal age, ssem in part to operate through an association between parity, sibship size, and birth weight. This analysis shows the importance of using longitudinal data in analysing such relations.

Birth Order↗
PubMed1990

Aging bone loss from the femur, spine, radius, and total skeleton.

In order to establish a comprehensive model for involutional bone loss, the following measurements were made of healthy white women: total body calcium by neutron activation analysis, bone density of the distal radius by single-photon absorptiometry, and dual-photon absorptiometry of the lumbar spine and femur (neck, Ward's triangle, and intertrochanteric areas). Longitudinal measurements were made for each of these skeletal sites except the femur. Evidence for a curvilinear component to the pattern of bone loss with aging was found for total body calcium and bone density of the radius, but not for the other measurements on analysis of cross-sectional data. Longitudinal studies confirmed that substantial bone loss begins only after menopause for the radius, whereas there is substantial premenopausal loss of bone from the lumbar spine. Prevention of vertebral osteoporosis requires maximizing bone mass before menopause. If longitudinal data confirm the model of linear rates of bone loss for the femur, there will be important implications for prevention of hip fractures.

Adult↗
PubMed2001

Variations in the measurement of resting energy expenditure in children with cystic fibrosis.

OBJECTIVE: To investigate in children with cystic fibrosis (CF) and children without CF: (1) the test-retest reproducibility of a 20 min resting energy expenditure (REE) measurement; and (2) the long-term reproducibility of REE measurements in children with CF using longitudinal data. DESIGN: Cross-sectional study and longitudinal cohort. SETTING: A tertiary referral paediatric hospital. SUBJECTS: A total of 31 (11 male, 20 female) children (aged 12.8+/-3.6 y) with CF and 32 (14 male, 18 female) healthy children without CF (aged 12.2+/-2.3 y) were enrolled in the short-term reproducibility study. Long-term REE measurement reproducibility was assessed in another 14 children (5 male, 9 female) with CF, comparing their initial REE measurement with a subsequent measurement 1-2 y later. METHODS: All children had measurements of height, weight, skinfold thickness and indirect calorimetry. RESULTS: There was no statistically significant difference in REE between repeated measurements in children with CF (mean+/-s.d., 6240+/-1280 and 6220+/-1315 kJ/24 h) and in the children without CF (6040+/-956 and 6015+/-943 kJ/24 h). For the children with CF, the intraclass correlation coefficient was 0.99 and for children without CF the intraclass correlation coefficient was 0.97. The measurement errors were 119 and 177 kJ, respectively. Approximately 80% of the variation in REE in the CF group and 70% in the group without CF was explained by fat-free mass (FFM). Analysis of the longitudinal CF data show there was no difference in REE between a child's first measurement (5140+/-1140 kJ) and their subsequent measurement (5460+/-1190 kJ), after adjustment for changes in body size between the measurements. CONCLUSION: This study has demonstrated that a short-term 20 min REE measurement is reproducible and therefore valid in children with CF and children without CF. These results also indicate that in children with CF, long-term REE measurements are reproducible.

Adolescent↗
PubMed1991

Estimation of spermarche from longitudinal spermaturia data.

A number of studies have dealt with determination of the age at onset of sperm emission (spermarche), based on observations of first occurrence of spermatozoa in urine. A major problem in this connection is the intermittent occurrence of sperm-negative urine samples after the achievement of spermarche. We have here considered an empirical Bayes approach for handling the probability of a sperm-positive urine sample after spermarche. The investigation was inspired by a concrete longitudinal study concerning 40 Scottish boys, which is used for illustration throughout. In this study, the urine was tested for spermatozoa from well before spermarche and every 3 months thereafter for at most 7 years. Some of the boys left the study earlier and techniques for handling such censoring were also developed.

Adolescent↗
PubMed1997

The association of modernization with dyslipidaemia and changes in lipid levels in the Polynesian population of Western Samoa.

BACKGROUND: Obesity and non-insulin-dependent diabetes mellitus (NIDDM) have increased in prevalence in Polynesian Western Samoans over the 13-year period 1978-1991, as the population undergoes an 'epidemiological transition'. METHODS: We therefore investigated changes in the frequency of dyslipidaemia over the same period in adults aged 25-74 years, and examined factors associated with dyslipidaemia in cross-sectional and longitudinal data. Subjects were drawn from three geographically defined locations representing different degrees of modernization. RESULTS: The age-standardized prevalence of dyslipidaemia increased in each location between 1978 (n = 1197) and 1991 (n = 1748) with the prevalence of hypercholesterolaemia (> or = 5.5 mmol/l) increasing from 18% to 36% (P < 0.001), and that of hypertriglyceridaemia (> or = 2.0 mmol/l) increasing from 9% to 15% (P < 0.001) in the capital city, Apia. In 1991 the highest serum concentrations of total, high density lipoprotein (HDL) and calculated low density lipoprotein (LDL) cholesterol were found in Poutasi (intermediate level of modernization), and the highest triglyceride levels in urbanized Apia. Higher levels of body mass index (BMI), waist-hip ratio (WHR), glucose intolerance, fasting insulin concentration, physical inactivity, educational level, and occupational status were all associated with adverse lipid levels in univariate data. Obesity (BMI in women, WHR in men) and survey location were the most important correlates of abnormal lipid levels in logistic regression models. Fasting insulin was also independently associated with high triglyceride levels in men, while in women the increasing levels of fasting insulin were associated with adverse levels of total, LDL and HDL cholesterol, and triglycerides. In longitudinal data (n = 311), lower baseline levels of cholesterol and triglycerides were associated with greater increases in either parameter at follow-up. Elevated fasting insulin and female gender also predicted increasing cholesterol concentrations, and urban residence predicted an increase in triglyceride levels. CONCLUSIONS: Current levels of dyslipidaemia in Western Samoa are similar to those observed in developed Western populations, and are increasing rapidly. These findings, considered along with the high prevalence of other cardiovascular disease risk factors in Samoans, including smoking, obesity and NIDDM, suggest that cardiovascular disease will be a major health concern in the future.

Adult↗
PubMed1978

Prediction of the mesiodistal widths of maxillary permanent canines and premolars.

Multiple regression equations for prediction of the mesiodistal widths of the maxillary canines and premolars were developed for the right and left sides of the arches of males and females. The equations were developed from longitudinal data taken from ninety-two Caucasian children (forty-six boys and forty-six girls) who participated in the Iowa Growth Study. The multiple regression equations, when compared with three currently used methods of prediction, were the best predictors. The newly developed equations and other prediction methods currently in use were tested on longitudinal data taken from a sample of forty-three Caucasian orthodontic patients (sixteen males and twenty-seven females). Again, the multiple regression equations had the best performance.

Adolescent↗
PubMed1998

Slicing the pie. Correlating HbA--values with average blood glucose values in a pie chart form.

OBJECTIVE: The purpose of this study was to define the correlation between HbA1c values and the percentage of home blood glucose (HBG) measurements within given ranges in a pie chart in three age-groups of subjects with type 1 diabetes. RESEARCH DESIGN AND METHODS: HbA1c values were compared with HBG measurements in subjects who did at least three blood glucose tests per day over 30 days in three age groups: 5-11, 12-16, and 17-35 years. The blood glucose values were arbitrarily divided into three groups, defined as the percentage of HBG measurements within, above, and below target range. Each range was then compared with the corresponding HbA1c value. Longitudinal data were also collected for 279 of the subjects after a mean of 139 days. RESULTS: A strong correlation (P = 0.001) was found between HbA1c values and the average blood glucose, and also with the percentage of HBG measurements within, above, and below target range in each of the three age-groups (P < 0.001). Analyses of longitudinal data showed a strong correlation of the changes in HbA1c values to the changes in blood glucose values. CONCLUSIONS: These data showed that a pie-shaped graph of the HBG data can be useful as a clinical parameter in helping patients and families attain desired HbA1c values.

Adolescent↗
PubMedDate not supplied

A longitudinal analysis of predictors of quitting smoking among participants in a self-help intervention trial.

Predictors of 7-day abstinence from smoking were identified among participants in a randomized self-help smoking-cessation intervention trial conducted from 1985 to 1988 in Seattle, WA. Subjects were adult smokers belonging to a health maintenance organization who responded to an offer of free quitting assistance. Self-reported smoking status was assessed at 8, 16, and 24 months following enrollment. Predictors of abstinence were identified by longitudinal data analysis using Generalized Estimating Equations (GEEs), a modeling approach which handles repeated-measures data and accommodates time-dependent as well as time-independent covariates. Seventeen items emerged as significant (p < .05) predictors, with odds ratios ranging from 1.3 to 2.1. While much of the previous work in smoking-cessation research has focused on demographic and smoking history variables, results of this study indicate that emphasis should also be placed on psychosocial/motivational factors and quitting activities as important predictors of abstinence. Longitudinal data analysis represents a powerful technique for handling correlated (repeated measures) data, which may prove very useful for future studies of smoking cessation as well as other dynamic processes.

Adult↗