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PubMed2000

Case study of attempts to enact self service tobacco display ordinances: a tale of three communities.

OBJECTIVE: To examine self service tobacco displays (SSTDs) and youth retail tobacco access by comparing longitudinal illegal tobacco sales rates in three communities in Santa Barbara County, California, that considered or implemented ordinances banning SSTDs. A confirmatory survey was also conducted to substantiate the longitudinal data. DESIGN: A longitudinal case study design was utilised. Five undercover tobacco buys were conducted between 1994 and 1997 (n = 332). In addition, one confirmatory survey was conducted in a geographically separated area, which had no ordinances banning SSTDs (n = 57). RESULTS: Decreases in youth buy rates were reported in all three communities. Most notably, the first city to enact a SSTD ban, Carpinteria, achieved a 0% sales rate, which was maintained throughout the study period. In contrast, Santa Barbara and Goleta experienced considerable drops in their illegal sales rates, but neither community obtained results as dramatic as those found in Carpinteria. The confirmatory survey showed that 32.1% of stores with SSTDs sold cigarettes to minors; this compares to a sales rate of 3.4% in stores without SSTDs (chi(2) (1) = 8.11, p = 0.004). CONCLUSIONS: Efforts to enact self service bans are likely to meet with retail and tobacco industry opposition, as was the case in this study's three communities. The process of community debate, resultant publicity surrounding the issue, and enactment of SSTD ordinances may serve to not only increase merchant awareness of youth tobacco laws and their penalties but also may contribute to reduced youth cigarette sales rates. Implications and limitations of the findings are discussed.

Adolescent↗
PubMed2000

Closing the knowledge-behavior gap in health promotion: the mediating role of self-efficacy.

Three cross-sectional data waves spanning 10 years (N = 2,055; 2,026; and 2,068) and 2 longitudinal data waves spanning 4 years (N = 1,384 and 1,151) from the Stanford Five-City Project (see Farquhar, Fortmann, Maccoby, & Haskell, 1985, for a full description of the project) were analyzed to determine whether diet self-efficacy mediated the relation between diet knowledge and behavior. In the cross-sectional data waves, knowledge-behavior correlations were greater among those with high (compared to low) self-efficacy. In the longitudinal data waves, knowledge-behavior correlations increased among those who increased their self-efficacy and decreased among those who decreased their self-efficacy. Recommendations are made for public health campaigns designed to improve individuals' health behaviors.

Adolescent↗
PubMed2002

Parameter estimation in longitudinal studies with outcome-dependent follow-up.

In many observational studies, individuals are measured repeatedly over time, although not necessarily at a set of prespecified occasions. Instead, individuals may be measured at irregular intervals, with those having a history of poorer health outcomes being measured with somewhat greater frequency and regularity; i.e., those individuals with poorer health outcomes may have more frequent follow-up measurements and the intervals between their repeated measurements may be shorter. In this article, we consider estimation of regression parameters in models for longitudinal data where the follow-up times are not fixed by design but can depend on previous outcomes. In particular, we focus on general linear models for longitudinal data where the repeated measures are assumed to have a multivariate Gaussian distribution. We consider assumptions regarding the follow-up time process that result in the likelihood function separating into two components: one for the follow-up time process, the other for the outcome process. The practical implication of this separation is that the former process can be ignored when making likelihood-based inferences about the latter; i.e., maximum likelihood (ML) estimation of the regression parameters relating the mean of the longitudinal outcomes to covariates does not require that a model for the distribution of follow-up times be specified. As a result, standard statistical software, e.g., SAS PROC MIXED (Littell et al., 1996, SAS System for Mixed Models), can be used to analyze the data. However, we also demonstrate that misspecification of the model for the covariance among the repeated measures will, in general, result in regression parameter estimates that are biased. Furthermore, results of a simulation study indicate that the potential bias due to misspecification of the covariance can be quite considerable in this setting. Finally, we illustrate these results using data from a longitudinal observational study (Lipshultz et al., 1995, New England Journal of Medicine 332, 1738-1743) that explored the cardiotoxic effects of doxorubicin chemotherapy for the treatment of acute lymphoblastic leukemia in children.

Adolescent↗
PubMedDate not supplied

The genetic contribution to pubertal growth and development studied by longitudinal growth data on twins.

Forty-eight pairs of MZ and like-sex DZ twins of Panjabi parentage were studied longitudinally for such pubertal changes as growth of genitalia, pubic, axillary and facial hair, change of voice and ejaculation of semen in boys, and growth of pubic and axillary hair, breast development and onset of menarche in girls, besides growth in height and weight. Mean intra-pair age differences are small and intra-pair correlations for age at different secondary sexual developments are higher in MZ twins than in DZ twins in both sexes. Mean intra-pair differences and intra-pair correlations for the time taken to pass from first stage to the final stage of development also present a similar picture. Intra-pair height and weight differences and differences in their growth velocities also indicate that MZ twins are more concordant than DZ twins throughout the adolescent growth period. These findings indicate a strong genetic component in regulating the pubertal changes as well as in the growth of height and weight in the two sexes. The role of environmental factors in at least some of the pubertal changes is also indicated.

Adolescent↗
PubMed1999

Models for forecasting chronic disease processes in adult and elderly populations: effects of stochasticity.

BACKGROUND: Forecasting the population health burden of chronic diseases requires models consistent with the relation, over time and in an uncertain environment, of risk factors and diseases at the individual level. There is now sufficient longitudinal data, and scientific understanding, of some chronic diseases to construct detailed process-models to better predict their population health burden and more realistically describe the effects of interventions. A crucial clement in constructing models is the way in which stochastic influences are described, e.g. are they allowed to interact over time with deterministic model features? METHODS: A review of statistical and forecasting models aimed to establish what ancillary data and scientific insights are necessary to describe multivariate stochastic health processes and their response to interventions. For circulatory diseases and cancer there exists sufficient longitudinal data and biological insight to construct stochastic multivariate process models. For other diseases, biological knowledge is less complete and there are fewer data sets where multiple risk factors are assessed longitudinally. Forecasting models for those diseases will then rely more heavily on theoretical assumptions about disease behaviour.

Chronic Disease↗
PubMed1999

Analysis of infant growth curves using multivariate adaptive splines.

In this paper, we study the effect of cocaine use by a pregnant woman on the growth of her infant after birth. Using a data set from a retrospective study, we found that cocaine use was a marginally significant contributor to the infant growth as measured by bodyweight. From a statistical point of view, the data represent a common, though complex, structure that has received little attention in the statistical literature. To analyze these data, we adopt and further enhance an approach developed recently called MASAL (multivariate adaptive splines for the analysis of longitudinal data). In addition to the fitting of growth curves, we demonstrate particularly how to explore and estimate the underlying covariance structures for the longitudinal data that were collected from a rather irregular schedule.

Biometry↗
PubMed2006

Methodological approach for assessing the cost-effectiveness of treatments using longitudinal observational data: the SOHO study.

OBJECTIVES: The objective of this study was to develop a method to allocate treatment effects when patients switch medication frequently in longitudinal observational studies and apply the approach to assess the cost-effectiveness of treatments in the Schizophrenia Outpatient Health Outcomes (SOHO) study. METHODS: Data were collected on patients at entry to the SOHO study at 3, 6, and 12 months. The 12-month follow-up period was considered as three epochs: 0-3 months, 3-6 months, and 6-12 months. Patients who switched treatment at 3 months had their new treatment considered as a new baseline observation, as these two 3-month observations provide two sets of information on the cost-effectiveness of a drug in the first 3 months after initiation. Multivariate regression analysis was used to adjust for baseline covariates. The model allowed for flexible functional forms, and the cost data were modeled using an exponential mean function. Bootstrapping assessed the uncertainty of the estimated parameters and incremental cost-effectiveness analysis decision rule. RESULTS AND CONCLUSIONS: We show the feasibility of the epoch analysis approach using data from the SOHO study comparing two antipsychotics. Estimates for the incremental cost and effectiveness per epoch over the full 12-month period are presented. Using the estimates of 200 bootstrap samples, we demonstrate how one drug is cost-effective compared with another.

Antipsychotic Agents↗
PubMed1983

Linked cross-sectional study for evaluating the effect on the microfilarial load of the onchocerciasis control programme.

When analysing incomplete longitudinal data (ie data which includes complete longitudinal results plus cross-sectional results plus partially longitudinal results) one can increase the sensitivity of the data by taking the correlation structure of the data into account. For the described data on onchocerciasis, the adapted method of Rao and Rao, called the Linked Cross-Sectional method, which estimates the mean microfilarial load for each passage and hence the differences between passages, taking into account the correlation between the same individuals measured at different times is such a method that reduces significantly the standard deviations of the mean responses and hence increases their sensitivity. The method takes into account the missing data nature of the results. It can be simply generalized to any number of passages.

Cross-Sectional Studies↗
PubMed1990

Somatosensory evoked potentials and adaptation to extrauterine life: a longitudinal study.

In order to compare longitudinal data with existing cross sectional extrauterine life data on somatosensory evoked potentials (SEPs), two groups of appropriate for gestational age optimal premature infants were studied. Group A consisted of 8 infants born between 34 and 36 weeks gestational age (GA). In this group, SEPs were recorded within 24 hours after delivery and then every 48-72 hours until discharge. Group B consisted of 7 infants born between 29 and 33 weeks GA. In these infants, SEPs were recorded at weekly intervals from the second week onwards. In group A, a marked decreased in the N1 latency was seen during the first week of life. Six infants had initial values above the normal range. During the second week of life this decrease paralleled the cross sectional data. In group B all the infants had a N1 latency within the normal range and the longitudinal data paralleled the cross sectional data. These findings must be taken into consideration when SEPs are used to assess the neurological integrity of the newborn during the first week of life.

Adaptation, Physiological↗
PubMed2000

Untreated periodontal disease in Indonesian adolescents. Longitudinal clinical data and prospective clinical and microbiological risk assessment.

BACKGROUND, AIMS: In order to investigate the r le of various putative clinical and microbiological risk markers, a longitudinal study was initiated in a young population deprived of regular dental care. In 1987 all inhabitants in the age range 15-25 years living in a village with approximately 2,000 inhabitants at a tea estate on Western Java, Indonesia, were examined clinically and microbiologically. In total, 167 subjects of the original group of 255 adolescents were re-examined in 1994. The material presented in this paper describes the clinical periodontal condition at baseline (1987) and at follow-up (1994), 7 years later. Furthermore, the relationship between progression of the disease and baseline clinical and microbiological data was assessed. METHODS: Plaque index (PI), bleeding on probing (BOP), pocket depth (PD), and attachment loss (AL) were scored at the approximal surfaces of the vestibular aspects of all teeth. The number of approximal surfaces of the Ramfjord teeth showing subgingival calculus was recorded. At baseline, the dorsum of the tongue, the buccal gingiva in the upper jaw, the saliva and the deepest bleeding pocket without clinical loss of attachment were sampled for microbiological examination with phase contrast microscopy and indirect immunofluorescence. RESULTS: Mean values at baseline and at follow-up were PI: 1.01 and 1.15, BOP: 0.80 and 1.16, PD 3.26 mm and 3.32 mm, AL: 0.33 mm and 0.73 mm, respectively. All parameters except PD showed a statistically significant increase over the 7-year period. The prevalence of the studied bacteria irrespective of the sample site was: A. actinomycetemcomitans 53%, P. gingivalis 88%, P. intermedia 100%, spirochetes 89% and motile micro-organisms 100%. At the full mouth level, logistic regression showed significant odds ratios for progressive disease with age (1.15), subgingival calculus (1.20) and subgingival presence of A. actinomycetemcomitans (4.61). Presence of any of the selected micro-organisms on the mucous membranes was not related with progressive disease. In order to study local factors to explain local disease activity, each subject was characterized using the sampled pocket, which was the deepest bleeding pocket without LA at baseline, as a single response site per patient. In this constrained design, the main statistical factors associated with progressive disease were presence of motile micro-organisms and the plaque score. CONCLUSIONS: This study identified 3 main risk markers for disease progression at the full mouth level: age, amount of subgingival calculus and subgingival presence of A. actinomycetemcomitans.

Adolescent↗
PubMed2004

Epidemiological theory, decision theory and mental health services research.

BACKGROUND: Mathematical models describing the epidemiology of major depression are potentially useful for epidemiological analyses, as decision support tools and in economic analyses. The objective of this project was to develop a Markov model based on epidemiological theory that may be useful for decision analysis and health services research. METHODS: Longitudinal data from a Canadian national survey, the National Population Health Survey (NPHS), were used. The NPHS has collected longitudinal data on a cohort of 17,262 subjects since 1994. The analysis employed a Markov tunnel in order to model the dependence of recovery probabilities on episode duration. RESULTS: Episode incidence ranged between 6.2 % per year in women under 35 to 0.26 % in men over the age of 65.A greater proportion of subjects over 35 years old reported episodes lasting more than 26 weeks. The probability of recovery declined with increasing episode duration, independently of sex. Under steady-state assumptions, a Markov model integrating these parameters predicted a point prevalence of approximately 2% in women and 1% in men under the age of 55. In older age groups, the predicted point prevalence declined in both sexes. CONCLUSIONS: These models support the hypothesis that sex differences in major depression prevalence are due primarily to differences in incidence rather than episode length. These results also indicate that there is no meaningful "central tendency" describing the distribution of episode length in major depression episode. Estimates of mean episode duration represent an intermixing of frequent brief episodes with infrequent protracted episodes. This finding may have important policy implications.

Adolescent↗
PubMed1986

Age related changes in visual acuity.

Longitudinal visual acuity assessments of men, and cross-sectional assessments of men and women in the Baltimore Longitudinal Study of Aging are presented. The longitudinal data relate presenting far, uncorrected far, presenting near and uncorrected near visual acuities to age. The cross-sectional data relate presenting far acuity to age. The prevalence of cataract, glaucoma and retinal pathologies are reported for the longitudinal sample at the time of their last vision test. The effect of visual pathologies in general, and cataract in particular, upon presenting far visual acuity was examined. The longitudinal data are consistent with cross-sectional data from previously published reports. Older persons who were free from specific visual pathologies exhibited an age-related decline in presenting far acuity as did those with documented visual pathologies. Despite the demonstrated loss in acuity with age, the majority of persons maintain at least fair acuity (20/40 or better) into their 80's.

Adult↗
PubMed1994

Utility of the force of infection model for assessing changes in the dynamics of bancroftian filarial infections.

Force of infection is measured in terms of the number of effective contacts that have been introduced into the population by infective vectors. The utility of such a measure in describing the dynamics of bancroftian filarial infection was tested. Force of infection (beta) incorporating the durations of patent period and pre-patent period was estimated for different age classes (assuming that it is constant in that particular age class) and it was found that the predicted post-control prevalences were close to the observed figures. Utility of Remme's model in areas with different transmission levels is discussed. It was examined whether the empirical function generally used in helminth infections to describe the functional relationship between beta and age could be used for lymphatic filariasis. The relationship between the two was not adequately described by the function. Force of infection, when compared with rate of acquisition calculated using longitudinal data, showed that this measure could be used as a crude estimate of rate of acquisition in places which do not have longitudinal data sets.

Adolescent↗
PubMed1998

Predictors of early retirement and rehabilitation for use in a screening to detect workers in need of rehabilitation.

In the German pension insurance sector a screening is being suggested to ensure the participation in rehabilitation measures of workers at risk of health-related early retirement. Screening presupposes empirical indicators of rehabilitation needs. A study is presented that determined predictors of early retirement and rehabilitation from longitudinal data for use in a screening for the selection of workers likely to be in need of rehabilitation. We gathered longitudinal data by conducting a second survey with a cohort for which the first survey had delivered clinical findings, lab. values, medical diagnoses and self reports regarding morbidity, medication, health-related behavior, family- and occupational-related strains, and sociodemographic information (first survey T0: 1975/76, n = 3.968; second survey T1: 1992/93, n = 28.463). The survey of T1 also comprised inquiries of the pension insurance institutions concerning the retirement and rehabilitation status for pension-insured study subjects (n = 1.794). Based on these subjects, using multi- and bivariate regression analysis, we determined those T0 variables which were significantly related to the events of early retirement (98 cases/357 controls), rehabilitation (127 cases/200 controls) and early retirement or rehabilitation (185 cases/270 controls) in the period T0-T1. The significant T0 variables were subsequently used for the definition of a selection index which measured rehabilitation need by a simple sum score (number of significant T0 variables present). We tested the discriminative power of this index for a subsample of the cohort (cases who retired early or underwent rehabilitation and controls). The index classified 68% of the cases correctly. The sensitivity reached 57% and the specificity 76%. In connection with this result, the long prognostic time interval (up to 17 years) has to be considered. In the case of screening the preselection of workers via the index would occur at the same time as the medical assessment of the actual need for rehabilitation. An earlier study showed that this would raise sensitivity and specificity of an index based on predictors of early retirement substantially.

Adult↗
PubMed1993

The relationship between age, gender and cognitive performance in the very old: the effect of selective survival.

OBJECTIVE: To determine the prevalence of cognitive disability as a function of advanced age and gender in elderly nursing home and community-dwelling populations. Since cognitive dysfunction is associated with increased mortality, we hypothesized that selective survival results in a decreased prevalence of cognitive disability in the oldest old. DESIGN: Cohort study. An analysis of 6-month longitudinal data obtained from a national probability sample of older persons in 260 nursing homes (n = 1951) and 2-year-longitudinal data obtained from a sample of community-dwelling older persons (n = 2947). MEASURES: In the nursing home sample, the primary outcome measure was cognitive performance score. In the community sample, cognitive performance was determined using the results of three orientation questions and assessment of decision-making ability. Cognitive performance and subsequent survival, controlling for various disease states and demographic factors, were examined in three age cohorts of men and women (ages 65-79, 80-89, 90-99). RESULTS: In the nursing home sample, the cognitive performance of very old men (> or = 90 years) was better than that of younger men (aged 80-89 years, P < 0.05) and very old women (age > or = 90 years, P = 0.001). Among 80-89-year-olds with poor cognitive performance, the 6-month mortality rate was higher in men than in women (38% vs 19%, P = 0.001). However, the mortality rates of men and women with good cognitive performance were not statistically different in any age group. Proportional-hazards regression analysis demonstrated that poor cognitive performance remained a powerful predictor of death among men aged 80-89 years with a relative risk of 2.7 (95% Cl, 1.19-3.17; P = 0.0006) after controlling for covariates. Results from the community sample lent support to our findings: within each age group, mortality rates for men and women with intact cognitive performance were not statistically different. However, in the two older age groups, the mortality rates of subjects with impaired cognitive performance were significantly greater for men than for women (P < 0.01 for both age groups). CONCLUSIONS: Decreased cognitive performance is significantly associated with mortality among elderly men. Survival by men who have relatively intact cognitive function results in a population of oldest men, those aged 90-99 years, with cognitive performance scores better than younger men or similarly-aged women. The same selective survival phenomenon was not observed among women. Thus, there may be less cognitive disability among very old men than previously expected.

Age Factors↗