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PubMed1999

Adjusting estimates of alveolar bone loss for missing observations: developing and testing a general model.

The occurrence of missing teeth is a vexing and growing problem in epidemiological studies of dental disease. The number of units of measurement (i.e., teeth/tooth sites) varies between persons and may affect summary statistics in descriptive studies as well as in analytical studies. The purpose of the present study was to develop a general model to adjust summary statistics for missing teeth. The proposed method was applied to alveolar bone loss in current smokers, former smokers, and non-smokers, from 45 to 64 years of age (n = 812). Alveolar bone loss was measured on bitewing radiographs. The adjustment method was based on the assumption that the probability of losing a tooth was an increasing function of alveolar bone loss. The main finding of the present study was that mean alveolar bone loss increased after adjustment for the number of missing teeth. This increase was larger for current smokers than for non-smokers, indicating that the effects of smoking were slightly underestimated when missing sites were ignored. Further research is required for the model to be applied to other data, estimating different types of dental disease with various degrees of disease prevalence and various numbers of missing teeth, and for validating the adjustment method by means of longitudinal data.

Age Factors↗

PubMed2001

The relationship between disease activity, joint destruction, and functional capacity over the course of rheumatoid arthritis.

OBJECTIVE: To investigate the relationship between functional capacity, disease activity, and joint destruction over the course of rheumatoid arthritis (RA). METHODS: The followup data on 378 patients with early RA (duration <1 year), included in an open, prospective study since 1985 at the Department of Rheumatology of the University Medical Center Nijmegen, were used. Functional capacity, disease activity, and joint destruction were assessed using the Health Assessment Questionnaire disability index (HAQ DI), the Disease Activity Score (DAS), and a modification of the sharp radiographic damage score, respectively. Multiple linear regression was used to model the data collected at 0, 3, 6, and 9 years after study start, to investigate which variables influenced functional capacity during the disease course. A general linear mixed model for longitudinal data, which included the variables identified as significant in the multiple linear regression models and several interaction terms between the variables, was run. RESULTS: On average, the functional capacity of the patients, as measured by the HAQ DI, worsened over the course of the disease after an initial improvement. After an initial reduction in the extent of disease activity, the mean DAS remained more or less stable over the course of the disease. The mean modified sharp joint damage score worsened over the course of the disease, with a slower progression rate later in the disease. In the multiple linear regression at 0, 3, and 6 years after study start, disease activity was found to be an important factor influencing functional capacity, and at 6 and 9 years, joint damage had an important effect on functional capacity. Furthermore, at 6 and 9 years, there was an interaction effect of joint destruction with disease activity. In the general linear mixed model, disease activity, joint damage, and an interaction effect of disease activity and joint damage were the main factors explaining functional capacity. CONCLUSION: The effect of disease activity and joint destruction on functional capacity changes over the course of the disease. In early RA, functional capacity is most associated with disease activity, and in late disease, with joint damage.

Adult↗

PubMed1994

Inter-country application of standard epidemiology tools in oral health.

If there is a single project which could demonstrate the intensive use of the WHO standard oral epidemiology methods which have been discussed and demonstrated in papers published elsewhere, it is the series of collaborative studies of oral health care systems referred to in brief as ICS-I and II. These consist of multi-country studies from which to assess the relative merits of different delivery systems based on interlinked clinical and sociological data for the consumer and sociological data for the provider. In both the ICS-I and II, each participating country team followed the same protocol and every effort was made to retain, for ICS-II, not only the same research strategy, but also as much of the methodology as possible. ICS-I covered the years 1973 to 1983: ICS-II began in 1988 and is due to end in 1995. A detailed description of the sampling, survey and analysis approaches is given in the first part of this article and highlights of the inter-country clinical data in the second part. Although ICS-I was hampered in its objective to compare relative strengths of delivery systems, or elements thereof, by the lack of comparative longitudinal data, its results had tremendous impact both for participating countries and others which could learn from the study findings. That impact was evident in the most practical form of wholesale changes in various systems and approaches and in application of study findings in constructing new systems. ICS-II data are intriguing both in the new examples they present and in comparisons over time, as well as in the improved methods developed as a result of lessons learned in ICS-I. The full report will be available in 1995.

Adolescent↗

PubMed1995

Impact of prior and current alcohol use on use of services by patients with depression and chronic medical illnesses.

OBJECTIVE: Alcohol use often co-occurs with other major chronic conditions, but its effect on health care utilization in this context is not understood. This study examines the impact of alcohol consumption on health care use by patients with chronic medical conditions or depression, or both. DATA SOURCES/STUDY SETTING: Data came from the Medical Outcomes Study, an observational study of patients from the offices of general medical providers and mental health specialists in three U.S. cities. STUDY DESIGN: Longitudinal data spanning four years for outpatient general medical visits and outpatient mental health visits were analyzed using a two-part model to assess the impact of alcohol use disorder, problem drinking, and current and past alcohol consumption on health care use by patients, controlling for patient demographics and health status. DATA COLLECTION/EXTRACTION METHODS: Data were collected from 2,546 adult patients with hypertension, diabetes, heart disease (congestive heart failure or myocardial infarction), and/or current major depression or subthreshold depression using periodic, self-report surveys detailing health care utilization and health status information. PRINCIPAL FINDINGS: Current alcohol consumption increases outpatient doctor visits, and problems related to current drinking decrease outpatient mental health visits. CONCLUSIONS: Patterns of alcohol consumption have an impact on both mental health and overall health care use by patients with chronic medical conditions or depression.

Adult↗

PubMed2004

Joint modeling of longitudinal and survival data via a common frailty.

We develop a joint model for the analysis of longitudinal and survival data in the presence of data clustering. We use a mixed effects model for the repeated measures that incorporates both subject- and cluster-level random effects, with subjects nested within clusters. A Cox frailty model is used for the survival model in order to accommodate the clustering. We then link the two responses via the common cluster-level random effects, or frailties. This model allows us to simultaneously evaluate the effect of covariates on the two types of responses, while accounting for both the relationship between the responses and data clustering. The model was motivated by a study of end-stage renal disease patients undergoing hemodialysis, where we wished to evaluate the effect of iron treatment on both the patients' hemoglobin levels and survival times, with the patients clustered by enrollment site.

Algorithms↗

PubMed1998

Longitudinal genetic analysis of menstrual flow, pain, and limitation in a sample of Australian twins.

Genetically informative longitudinal data about menstrual disorders allow us to address the extent to which the same genetic risk mechanisms are operating throughout the reproductive life cycle. We investigate the relative contributions of genes and environment to individual differences in menstrual symptomatology reported at two waves, 8 years apart, of a longitudinal Australian twin study. Twins were questioned in 1980-1982 and 1988-1990 about levels of menstrual pain, flow, and perceived limitation by menses. Longitudinal genetic analysis was based on 728 pairs (466 MZ and 262 DZ) who were regularly menstruating at both survey waves. A bivariate Cholesky model was fitted to the two-wave data separately for flow, pain, and limitation variables. The baseline model comprised common genetic and environmental factors influencing responses at both waves and specific effects influencing only the second-wave response. We also included age as a covariate in the model. Proportions of the longitudinally stable variance in menstrual flow, pain, and limitation attributable to genetic and individual environmental effects were calculated for the best-fitting models. Genetic factors accounted for 39% of the longitudinally stable variation in menstrual flow, 55% for pain, and 77% for limitation. The remaining stable variance was due to individual environmental factors (61, 45, and 23%, respectively). Therefore the stable variance over the 8-year interval was largely environmentally influenced for menstrual flow, was approximately equally determined by genetic and by nonshared environmental influences in the case of pain, and was due almost entirely to genetic influences for limitation by periods. We demonstrate for the first time that the same genetic influences are operative throughout the reproductive life span.

Adolescent↗

PubMed2004

The quality of girls' diets declines and tracks across middle childhood.

BACKGROUND: Food group intakes by US children are below recommendations and micronutrient inadequacies have been reported. There are few longitudinal data that focus on developmental changes in food and nutrient intake from early to middle childhood. We examined changes in nutrient and food group intakes over time and the tracking of intakes across middle childhood in a longitudinal sample of girls. METHODS: Three multiple-pass 24-hour diet recalls were conducted in a sample of 181 non-Hispanic White girls at ages 5, 7, and 9 years. Food and nutrient data were averaged across 3 days. Analyses of time effects were conducted using repeated measures analysis of variance and tracking of intakes was assessed via rank analysis. RESULTS: We found significant decreases in nutrient densities (intakes per 1000 kcal) of vitamins C and D, calcium, phosphorus, magnesium and zinc at age 9. Girls maintained their relative quartile positions for these micronutrients from ages 5-9. Analysis of food group data showed similar trends. At age 9, significantly fewer girls were meeting the recommendations for dairy, fruit and vegetable servings than at age 5 and girls also tended to remain in their respective quartiles over time, especially for fruit and dairy intakes. CONCLUSIONS: These results highlight the importance of developing healthy eating practices during early childhood when caretakers have considerable control over children's food intake.

Journal Article↗

PubMed2002

Marginally specified generalized linear mixed models: a robust approach.

Longitudinal data modeling is complicated by the necessity to deal appropriately with the correlation between observations made on the same individual. Building on an earlier nonrobust version proposed by Heagerty (1999, Biometrics 55, 688-698), our robust marginally specified generalized linear mixed model (ROBMS-GLMM) provides an effective method for dealing with such data. This model is one of the first to allow both population-averaged and individual-specific inference. As well, it adopts the flexibility and interpretability of generalized linear mixed models for introducing dependence but builds a regression structure for the marginal mean, allowing valid application with time-dependent (exogenous) and time-independent covariates. These new estimators are obtained as solutions of a robustified likelihood equation involving Huber's least favorable distribution and a collection of weights. Huber's least favorable distribution produces estimates that are resistant to certain deviations from the random effects distributional assumptions. Innovative weighting strategies enable the ROBMS-GLMM to perform well when faced with outlying observations both in the response and covariates. We illustrate the methodology with an analysis of a prospective longitudinal study of laryngoscopic endotracheal intubation, a skill that numerous health-care professionals are expected to acquire. The principal goal of our research is to achieve robust inference in longitudinal analyses.

Biometry↗

PubMed1989

[Computer survey of the rehabilitation data and social conditions of children with motor disabilities in Györ-Sopron and Baranya Counties].

To investigate the occurrence of motor disability a pilot study was carried out in the total children's population of Györ-Sopron county and in 57% of the children of Baranya county by computer-based questionnaires. The data of the 492 motor handicapped children were analysed by 55 computer programs. These programs are constructed for the analysis of the somatic and mental health, schooling, rehabilitation possibilities, social background, care of these children and their further needs for specialists and institutions. This procedure is suitable for national and longitudinal data collection and for the complex registration of the status of these children.

Adolescent↗

PubMed1979

Aspects of phonological acquisition during articulation training.

Acquisition of correct /s/ over time was studied in five misarticulating children and compared to data reported for younger children during normal phonological development. Changes in production of /s/ as the children were learning to produce /s/ were examined in untrained syllables session by session. These longitudinal data were explored for patterns reported to occur in normal acquisition. It was found that the misarticulating children typically shifted their responses from correct to incorrect during the acquisition period; this may be attributed to competing rules operating during the early stages of acquisition similar to the rules proposed to be operating during morphological acquisition. The children varied in the time required to acquire correct production which is comparable to the variability reported in normal acquisition. Individual learning strategies were noted in the children's productions of consonant clusters which correspond to the proposed stages of development in normal phonological acquisition.

Articulation Disorders↗

PubMed2006

A corrected pseudo-score approach for additive hazards model with longitudinal covariates measured with error.

In medical studies, it is often of interest to characterize the relationship between a time-to-event and covariates, not only time-independent but also time-dependent. Time-dependent covariates are generally measured intermittently and with error. Recent interests focus on the proportional hazards framework, with longitudinal data jointly modeled through a mixed effects model. However, approaches under this framework depend on the normality assumption of the error, and might encounter intractable numerical difficulties in practice. This motivates us to consider an alternative framework, that is, the additive hazards model, about which little research has been done when time-dependent covariates are measured with error. We propose a simple corrected pseudo-score approach for the regression parameters with no assumptions on the distribution of the random effects and the error beyond those for the variance structure of the latter. The estimator has an explicit form and is shown to be consistent and asymptotically normal. We illustrate the method via simulations and by application to data from an HIV clinical trial.

Acquired Immunodeficiency Syndrome↗

PubMed2006

Developmental trajectories of adolescent popularity: a growth curve modelling analysis.

Growth curve modelling was used to examine developmental trajectories of sociometric and perceived popularity across eight years in adolescence, and the effects of gender, overt aggression, and relational aggression on these trajectories. Participants were 303 initially popular students (167 girls, 136 boys) for whom sociometric data were available in Grades 5-12. The popularity and aggression constructs were stable but non-overlapping developmental dimensions. Growth curve models were run with SAS MIXED in the framework of the multilevel model for change [Singer, J. D., & Willett, J. B. (2003). Applied longitudinal data analysis. Oxford, UK: Oxford University Press]. Sociometric popularity showed a linear change trajectory; perceived popularity showed nonlinear change. Overt aggression predicted low sociometric popularity but an increase in perceived popularity in the second half of the study. Relational aggression predicted a decrease in sociometric popularity, especially for girls, and continued high-perceived popularity for both genders. The effect of relational aggression on perceived popularity was the strongest around the transition from middle to high school. The importance of growth curve models for understanding adolescent social development was discussed, as well as specific issues and challenges of growth curve analyses with sociometric data.

Adolescent↗

PubMed2006

'Stickiness' and 'inflow' as proxy measures of the relative attractiveness of various sub-sectors of nursing employment.

Workplaces vary in their ability to recruit and retain workers. We introduce two new concepts which can be used as proxy measures of the relative attractiveness of a particular setting, where setting can be defined narrowly (e.g., a particular organization) or broadly (e.g., a sub-sector). "Stickiness" is defined as the transition probability that an employee stays in a given setting; "inflow" as the proportion of new employees. Using a longitudinal dataset of all nurses registered with the College of Nurses of Ontario, Canada 1993-2003, employment site was used to define consistent sectors and sub-sectors. Each nurse was assigned to one sector/sub-sector per year. Stickiness and inflow values were calculated for each sub-sector, and the trends across time were analyzed. Results show that despite shrinkage in the hospital sub-sectors, hospitals remained highly sticky. The expanding sub-sectors, in general, appear relatively unattractive to nurses; they couple medium/low stickiness with high inflow. Considerable variability across sub-sectors was evident. Stickiness and inflow were found to be useful as proxy measures of the relative attractiveness of the various sub-sectors of nursing employment over time. The concepts may be used for other workforces for which linked longitudinal data are available.

Employment↗

PubMed2003

Association between physical activity and mental disorders among adults in the United States.

BACKGROUND: The objective of this study was to determine the association between regular physical activity and mental disorders among adults in the United States. METHODS: Multiple logistic regression analyses were used to compare the prevalence of mental disorders among those who did and did not report regular physical activity using data from the National Comorbidity Survey (n = 8098), a nationally representative sample of adults ages 15-54 in the United States. CONCLUSIONS: Slightly over one-half of adults reported regular physical activity (60.3%). Regular physical activity was associated with a significantly decreased prevalence of current major depression and anxiety disorders, but was not significantly associated with other affective, substance use, or psychotic disorders. The association between regular physical activity and lower prevalence of current major depression (OR = 0.75 (0.6,0.94)), panic attacks (OR = 0.73 (0.56, 0.96)), social phobia (OR = 0.65 (0.53, 0.8)), specific phobia (OR = 0.78 (0.63, 0.97)), and agoraphobia (OR = 0.64 (0.43, 0.94)) persisted after adjusting for differences in sociodemographic characteristics, self-reported physical disorders, and comorbid mental disorders. Self-reported frequency of physical activity also showed a dose-response relation with current mental disorders. DISCUSSION: These data document a negative association between regular physical activity and depressive and anxiety disorders among adults in the U.S. population. Future research that investigates the mechanism of this association using longitudinal data to examine the link between physical activity and incident and recurrent mental disorders across the lifespan is needed.

Adolescent↗

PubMed1992

Air pollution and school absenteeism among children in Mexico City.

To determine the acute effects of ozone exposure, the authors conducted a short follow-up study of respiratory illness in a population of 111 preschool children frequently exposed to ozone levels that regularly exceed 0.120 parts per million (ppm). The children attended a private kindergarten in the southwestern part of Mexico City. Parents completed a questionnaire on demographic data, medical history, and potential sources of indoor air pollution. To determine the relation of ozone and respiratory-related school absenteeism, the authors used a logistic regression model for longitudinal data. During the 3-month follow-up, 50% of the children had at least one respiratory-related absenteeism period, and 11.7% had two or more. Children exposed for 2 consecutive days to high ozone levels (> or = 0.13 ppm) had a 20% increment in the risk of respiratory illness. For children exposed for 2 consecutive days to a high ozone level and the previous day to low temperature (< or = 5.1 degrees C), the risk reached 40% (odds ratio = 1.44, 95% confidence interval 1.37-1.52). This study suggests that ozone exposure might be positively associated with the risk of respiratory illness in children and that it may have an interactive effect with low temperature exposure.

Absenteeism↗

PubMed2003

Statistical approaches to assessing the effects of neutralizing antibodies: IFNbeta-1b in the pivotal trial of relapsing-remitting multiple sclerosis.

Carefully conducted large-scale clinical trials have provided strong evidence that type I interferons favorably influence clinical and MRI outcomes in patients with multiple sclerosis. Some patients develop neutralizing antibodies (NAbs) to these treatments, reflecting an immune system response. The clinical significance of these NAbs has been uncertain because titers vary widely, and even highly elevated NAb titers decrease to undetectable levels in some patients. Whether NAbs decrease the efficacy of these treatments is a critically important scientific question. We argue that a longitudinal data analysis is the most appropriate approach to address this question.

Antibodies↗

PubMed1996

[Adult stature prediction in boys according to the Khamis-Roche method and proposed regression equations].

The purpose of the present study was to compare the prediction error of boys' adult stature depending on the Khamis-Roche method and regression equations proposed by the present author. The study is based on longitudinal data gathered in Kraków in between 1976-1988 and in 1994 (138 healthy boys aged 6-24 years). The predicted value from 7 to 16 years was compared with the body height measured during the last examination which was considered to provide adult stature. The equations proposed by the author were based on multiple regression analysis assessing the strength of the linear relationship between attained final height and other potentially, predictive measures of adult stature. The equations, which take into consideration current height, body weight at a given age, midparent's stature and, additionally, sexual maturity from 13 years, had the greatest predictive value. In the Khamis-Roche method, a tendency to underestimate the predicted adult height of Polish boys appeared. Median absolute error was from 2.2 to 1.4 cm at the age of 7 to 16 and was smaller for most age groups in the equations proposed by me. The proposed equations may be used in the prediction of adult stature of healthy boys, since they are based on the most current data, which is of importance in secular trends and interpopulation differentiation.

Adolescent↗

PubMed2005

Patient-initiated switching between private and public inpatient hospitalisation in Western Australia 1980 - 2001: an analysis using linked data.

BACKGROUND: The aim of the study was to identify any distinct behavioural patterns in switching between public and privately insured payment classifications between successive episodes of inpatient care within Western Australia between 1980 and 2001 using a novel 'couplet' method of analysing longitudinal data. METHODS: The WA Data Linkage System was used to extract all hospital morbidity records from 1980 to 2001. For each individual, episodes of hospitalisation were paired into couplets, which were classified according to the sequential combination of public and privately insured episodes. Behavioural patterns were analysed using the mean intra-couplet interval and proportion of discordant couplets in each year. RESULTS: Discordant couplets were consistently associated with the longest intra-couplet intervals (ratio to the average annual mean interval being 1.35), while the shortest intra-couplet intervals were associated with public concordant couplets (0.5). Overall, privately insured patients were more likely to switch payment classification at their next admission compared with public patients (the average rate of loss across all age groups being 0.55% and 2.16% respectively). The rate of loss from the privately insured payment classification was inversely associated with time between episodes (2.49% for intervals of 0 to 13 years and 0.83% for intervals of 14 to 21 years). In all age groups, the average rate of loss from the privately insured payment classification was greater between 1981 and 1990 compared with that between 1991 and 2001 (3.45% and 3.10% per year respectively). CONCLUSION: A small but statistically significant reduction in rate of switching away from PHI over the latter period of observation indicated that health care policies encouraging uptake of PHI implemented in the 1990s by the federal government had some of their intended impact on behaviour.

Journal Article↗