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Results for “longitudinal data”

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PubMed2006

Comparison of variance estimation approaches in a two-state Markov model for longitudinal data with misclassification.

We examine the behaviour of the variance-covariance parameter estimates in an alternating binary Markov model with misclassification. Transition probabilities specify the state transitions for a process that is not directly observable. The state of an observable process, which may not correctly classify the state of the unobservable process, is obtained at discrete time points. Misclassification probabilities capture the two types of classification errors. Variance components of the estimated transition parameters are calculated with three estimation procedures: observed information, jackknife, and bootstrap techniques. Simulation studies are used to compare variance estimates and reveal the effect of misclassification on transition parameter estimation. The three approaches generally provide similar variance estimates for large samples and moderate misclassification. In these situations, the resampling methods are reasonable alternatives when programming partial derivatives is not appealing. With smaller chains or higher misclassification probabilities, the bootstrap method appears to be the best choice.

Analysis of Variance↗

PubMed1992

Deterioration on the Blessed test in Alzheimer's disease: longitudinal data and their implications for clinical trials and identification of subtypes.

One hundred eleven patients with probable Alzheimer's disease (AD) were given the Blessed test (BT) of information, memory, and concentration (scored 0-33) at 6-month intervals over periods of 6-96 months. For each patient, the change in the total BT score between pairs of visits at 6- and 12-month intervals was measured. Mean deterioration scores over 6 and 12 months were 2.2 (SD = 3.2) and 4.1 (SD = 4.1) points, respectively. There was no significant correlation between degree of dementia on the BT and the rate of deterioration. Gender, age of onset, and family history had no significant effect on the rate of deterioration. The implications of the results for treatment trials and investigations of clinical heterogeneity are discussed.

Adult↗

PubMed2004

Adaptation to life after surgical removal of the bladder-an application of graphical Markov models for analysing longitudinal data.

Graphical Markov models have been developed particularly for the analysis of observational data. They allow the control of various background variables when analysing theoretically relevant associations. This paper demonstrates the application and some advantages of graphical Markov models in comparison to conventional statistical analyses. The aim of the study was to identify patients at risk for developing decreased health-related quality of life (QoL) after cystectomy and to explore the influence of coping on QoL in this situation. Therefore, the method was applied to analyse the data of a prospective study, in which 81 patients with bladder cancer were interviewed pre-operatively and in a 1-year follow-up. QoL was assessed both times, and two basic coping strategies (active and depressive) were measured preoperatively. The explanatory variables of theoretical interest were active and depressive coping strategies. As a result of the analysis, relevant proportions of variance in the development of QoL could be explained by the suggested model (60 per cent in mental component, 40 per cent in physical component of QoL). Active coping was positively related to QoL, depressive coping negatively. These effects were linear in the physical component of QoL, moderated by working status and the type of urinary diversion in the mental component of QoL.

Adaptation, Psychological↗

PubMedDate not supplied

Growth of Wrocław children aged 0-2 years born in 1964-65 and in 1973-75: longitudinal data.

One hundred boys and 100 girls born in Wrocław, Poland in 1964-65 and the same number of children born in 1973-75 were measured every month during the first year of life and every three months during the second. The characters investigated were body length and weight, head circumference and Rohrer's index. Generally, it seems that during the decade considered body dimensions in girls have shown slight secular increases while in boys these dimensions have remained stable or have decreased. Consequently, sex differences have decreased. Values of Rohrer's index indicate that children born in the 1970s are slimmer than those born in the 1960s. This particularly concerns girls. It seems that the explanation of these changes should be sought in the lack of improvement of the socio-living conditions and the increase of harmful environmental influences, to which boys may react quicker. With girls, the secular changes may persist for some time, since their reaction to environmental stimuli is slower.

Anthropometry↗

PubMed1996

Toward an understanding of NSAID-related adverse events: the contribution of longitudinal data.

The ARAMIS (Arthritis, Rheumatism and Ageing Medical Information System) databanks have been used to objectify and quantify drug toxicity. The relative risk of a gastrointestinal (GI)-provoked hospitalization was more than five times greater in patients taking non-steroidal anti-inflammatory drugs (NSAIDs) than in non-NSAID-treated patients, with an excess hospitalization rate of 1.3% per annum. Additionally, there was an excess GI-related death rate of around 3% in rheumatoid arthritis (RA) patients compared with the normal population. Age, previous NSAID-related GI events, prednisone use, higher doses and greater disability predicted high-risk patients. A toxicity index showed clear differences between NSAIDs, with aspirin, salsalate and ibuprofen emerging as the least toxic, and meclofenamate and indomethacin as the most toxic. Disease modifying anti-rheumatic drugs (DMARDs) were, surprisingly, found to have similar toxicity scores to the NSAIDs. This supports the contemporary practice of employing DMARDs earlier and more aggressively in the course of RA.

Aged↗

PubMed2001

Institutionalization in the elderly: the role of chronic diseases and dementia. Cross-sectional and longitudinal data from a population-based study.

A population-based study of 1810 persons, aged 75+, was investigated to evaluate the role of dementia and other chronic diseases as determinants of institutionalization in the elderly. The study population was examined at baseline and after a 3-year interval. After adjustment for sociodemographic characteristics, functional dependence, dementia, cerebrovascular disease and hip fracture were associated with living in an institution at baseline. Additionally, functional dependence, hip fracture and dementia were also associated with moving to an institution during the 3-year follow-up. In a similar analysis, including only nondemented subjects, the Mini-Mental State Examination emerged as one of the strongest determinants. The population attributable risk percentage of institutionalization during the 3-year follow-up due to dementia was 61%. This study confirms that dementia and cognitive impairment are the main contributors to institutionalization in the elderly, independently of their sociodemographic status, social network, or functional status.

Age Distribution↗

PubMed2004

Genetic and environmental influences on pubertal development: longitudinal data from Finnish twins at ages 11 and 14.

To study sources of individual differences in pubertal development, the authors fit a sex-limitation common factor model to data reported, at ages 11 and 14 years, by 1,891 twin pairs on items that comprise the Pubertal Development Scale (PDS; A. C. Petersen, L. Crockett, M. Richards, & A. Boxer, 1988). The model divides variation into a general pubertal factor and item-specific variation and, in addition, decomposes it into constituent sources. In both boys and girls, genetic influences made the largest contribution to variance common to PDS items. Genetic and nonshared environmental factors accounted for variation specific to PDS items in boys, whereas for girls, common environmental influences were added for growth spurt and menarcheal status. For both common and item-specific variation, genetic effects were partially sex specific. Subsidiary analyses found accelerated maturation in both boys and girls who at age 14 were reared in father-absent homes.

Adolescent↗

PubMed2002

Small-sample inference for incomplete longitudinal data with truncation and censoring in tumor xenograft models.

In cancer drug development, demonstrating activity in xenograft models, where mice are grafted with human cancer cells, is an important step in bringing a promising compound to humans. A key outcome variable is the tumor volume measured in a given period of time for groups of mice given different doses of a single or combination anticancer regimen. However, a mouse may die before the end of a study or may be sacrificed when its tumor volume quadruples, and its tumor may be suppressed for some time and then grow back. Thus, incomplete repeated measurements arise. The incompleteness or missingness is also caused by drastic tumor shrinkage (<0.01 cm3) or random truncation. Because of the small sample sizes in these models, asymptotic inferences are usually not appropriate. We propose two parametric test procedures based on the EM algorithm and the Bayesian method to compare treatment effects among different groups while accounting for informative censoring. A real xenograft study on a new antitumor agent, temozolomide, combined with irinotecan is analyzed using the proposed methods.

Algorithms↗

PubMed2004

Gait slowing as a predictor of incident dementia: 6-year longitudinal data from the Sydney Older Persons Study.

Current definitions for the preclinical phase of dementia focus predominantly on cognitive measures, with particular emphasis on memory and the prediction of Alzheimer's disease. Incorporation of non-cognitive, clinical markers into preclinical definitions may improve their predictive power. The Sydney Older Persons Study examined 6-year outcomes of 630 community-dwelling participants aged 75 or over at recruitment. At baseline, participants were defined as demented, cognitively intact or having a syndrome possibly representing the preclinical phase of Alzheimer's disease, vascular dementia, an extrapyramidal dementia or various combinations of the three. Those with cognitive impairment in combination with gait and motor slowing were the most likely to dement over the 6-year period (OR 5.6; 95% CI 2.5-12.6). This group was also the most likely to die (OR 3.3; 95% CI 1.6-6.9). White matter indices on MRI scanning were not consistently correlated with gait abnormalities. Simple measures of gait may provide useful clinical tools, assisting in the prediction of dementia. However, the underlying nature of these deficits is not yet known.

Aged↗

PubMed1992

A parametric family of correlation structures for the analysis of longitudinal data.

In epidemiological settings, we are often faced with numerous short time series, and a parsimonious parametrization of the correlation structure is desired in order to optimize the efficiency of the estimation procedure. We propose a damped exponential correlation structure for modeling multivariate Gaussian outcomes. The correlation between two observations separated by s units of time is modeled as gamma s theta, where gamma is the correlation between elements separated by one s-unit, and theta is a damping parameter. For (theta = 0), (theta = 1), and theta----infinity), the correlation structures of compound symmetry, first-order autoregressive, and first-order moving average processes are obtained. Although the AR(2) dependency structure, and the combination of random effects and AR(1) errors are not special cases of the proposed parametric family, these structures can be well approximated within the family for short time series. Maximum likelihood methods for parameter estimation and interpretations of intermediate models (0 less than theta less than 1) are discussed in the context of modeling pulmonary function in an adult population in The Netherlands and T-cell subsets in homosexual men infected with human immunodeficiency virus Type I.

Adult↗

PubMed2006

Sexual behaviour in Russia: who exhibits a higher risk? Evidence from longitudinal data.

The object of the paper is to assess the social and economic determinants of 'risky' sexual behaviour in Russia. We used secondary data from a nationally representative survey of 6168 persons between the ages of 14 and 49 years conducted in 2001 and 2003. Sexual risk is defined as having had unprotected (without a condom) penetrative sexual intercourse with two or more partners in the 12 months preceding the survey. The analysis uses a multivariate random effects model. There was a significant reduction in sexually risky behaviour between 2001 and 2003. Men and those employed exhibited significantly greater risk as did those between the ages of 25 and 44 years. Those who considered themselves economically secure also were significantly more likely to have had risky sexual contacts in the year before the survey. Those with only a basic education were significantly less likely to exhibit such behaviour. Those at highest risk in Russia of contracting sexually transmitted diseases (STDs) including HIV are not in marginal or socially excluded groups but instead are part of the core economically active population.

Adolescent↗

PubMed1997

Assessing the effects of interventions using longitudinal data with samples subject to selection.

Consider an uncontrolled study in which subjects are selected to start a new intervention because one or more previous measurements of a variable are within a particular range. Our aim is to use the repeated values obtained prior and subsequent to the start of the intervention to assess the effects of its introduction. However, because selection is based on the same variable as is being used to assess efficacy, regression to the mean will confound the interpretation of the results. In this paper, we present a likelihood-based method for evaluating the effects of the intervention using the repeated measurements while adjusting for the effects of the selection. The method uses a linear model to describe each subject's pattern of responses before and after the start of the new intervention. Additionally, it assumes that the effect of starting the new intervention on an individual's intercept and slope is the same for all subjects. However, no distributional assumption is made about the pattern of the linear model across subjects, thus making it particularly appropriate for phase I/II studies when patient histories on those not selected for the study are not available.

Acquired Immunodeficiency Syndrome↗

PubMed1998

Using longitudinal data to define the perimenopause by menstrual cycle characteristics.

OBJECTIVES: To determine which aspects of menstrual change best predict time to postmenopause. METHODS: A total of 250 Australian-born women aged 45-55 years were divided into five menstrual status categories: Group I reported no change in menstrual flow or frequency; Group II reported change in flow; Group III reported change in frequency; Group IV reported change in both frequency and flow; and Group V reported between 3 and 11 months of amenorrhea. Menstrual status groups were compared on baseline data for age, hormone levels, hot flushes and self-rated menopausal status. The proportion of women moving to postmenopause in subsequent years was compared using 4 years of follow-up data. RESULTS: Women in Group V were older, had lower estradiol and inhibin levels, higher follicle stimulating hormone levels, and were more likely to report hot flushes, and to self-rate themselves as having started the menopausal transition, compared with the women who had menstruated in the last 3 months (Groups I-IV). Groups I and II were similar in age and hormonal status, as were Groups III and IV. The proportion of women who had moved to postmenopausal status in the 4 years after baseline were 12%, 14%, 58%, 53% and 94% for Groups I-V, respectively. CONCLUSIONS: Amenorrhea is the best predictor of future menopause followed by changes in menstrual frequency. Change in flow only was not predictive of future menopause. A two-stage classification scheme is suggested for defining the perimenopause. 'Early perimenopause' is defined as the self-reporting of changes in menstrual frequency over the last year, and 'late perimenopause' is defined as the self-report of 3-11 months of amenorrhea.

Amenorrhea↗

PubMed2004

Does breastfeeding protect against pediatric overweight? Analysis of longitudinal data from the Centers for Disease Control and Prevention Pediatric Nutrition Surveillance System.

OBJECTIVE: To examine whether increasing duration of breastfeeding is associated with a lower risk of overweight in a low-income population of 4-year-olds in the United States. METHODS: Visit data were linked to determine prospectively the duration of breastfeeding (up to 2 years of age) and weight status at 4 years of age. Overweight among 4-year-old children was defined as a body mass index (BMI)-for-age at or above the 95th percentile based on the 2000 Centers for Disease Control and Prevention growth charts. Logistic regression was performed, controlling for gender, race/ethnicity, and birth weight. In a subset of states, links to maternal pregnancy records also permitted regression analysis controlling for mother's age, education, prepregnancy BMI, weight gain during pregnancy, and postpartum smoking. Data from the Pediatric Nutrition Surveillance System, which extracts breastfeeding, height, and weight data from child visits to public health programs, were analyzed. In 7 states, data were linked to Pregnancy Nutrition Surveillance System data. A total of 177 304 children up to 60 months of age were included in our final pediatric-only analysis, and 12 587 were included in the pregnancy-pediatric linked analysis. RESULTS: The duration of breastfeeding showed a dose-response, protective relationship with the risk of overweight only among non-Hispanic whites; no significant association was found among non-Hispanic blacks or Hispanics. Among non-Hispanic whites, the adjusted odds ratio of overweight by breastfeeding for 6 to 12 months versus never breastfeeding was 0.70 (95% confidence interval: 0.50-0.99) and for >12 months versus never was 0.49 (95% confidence interval: 0.25-0.95). Breastfeeding for any duration was also protective against underweight (BMI-for-age below the 5th percentile). CONCLUSION: Prolonged breastfeeding is associated with a reduced risk of overweight among non-Hispanic white children. Breastfeeding longer than 6 months provides health benefits to children well beyond the period of breastfeeding.

Adult↗

PubMed1992

The natural history of multiple sclerosis: a regional study with some longitudinal data.

A regional survey of multiple sclerosis (MS) patients in Wellington, New Zealand in 1983 identified 245 patients, giving a prevalence (all categories included) of 72 per 100,000. Retrospective review of the history and medical records identified a poorer prognosis for disability where there was progressive onset of symptoms, secondary progression after a remitting phase, older age of onset (40 years or more), or a motor syndrome involving the limbs at presentation. In 1983 follow up data were obtained on 96 patients who were seen during a previous survey in 1968. For those with definite or probable MS, progression to severe disability (Kurtzke disability status scale (DSS) 6-9) or death (DSS 10) was seen in 26/34 with moderate disability (DSS 3-5) in 1968 and in only 5/29 with mild disability (DSS 0-2). When the analysis is confined to those with symptoms for at least five years in 1968, severe disability or death from MS occurred in 22/30 with moderate and 4/19 with mild disability (chi 2 = 10.8, p = 0.001). It is concluded that the patient's established disability level after five years of illness is a useful, but not infallible, prognostic indicator. From the follow up of the 1968 patients, the probability of MS-related mortality for a given disease duration was calculated. Using this survival distribution to adjust the disability ratings in the 1983 population, it was found that the proportion with mild disability decreased steadily with increasing disease duration, reaching 14% when the disease duration was more than 25 years.

Adolescent↗

PubMed2004

Transition models to assess risk factors for new and persistent trypanosome infections in cattle-analysis of longitudinal data from the Ghibe Valley, southwest Ethiopia.

The objective of this study was to apply transition models to distinguish between factors associated with both incident and persistent trypanosome infections. Data collected from 1561 cattle were analyzed from a long-term study involving 8 herds in which both trypanosome infections (a total of 56,931 cattle sampling-months) and tsetse (Glossina spp.) challenge were monitored monthly from March 1986 to March 1998. Both pour-on and insecticide-target tsetse control programs and mass treatment with diminazene aceturate before tsetse control were associated with significant decreases in both incidence and persistence of trypanosome infection relative to noncontrol periods, as were seasonal and sex effects. The magnitudes of the effects were, however, often different for new and persistent infections. For persistence of infection, there were 2 trends. In general, the duration of infection increased during the study, despite the regular treatment with diminazene aceturate. The transition model had 2 major benefits. The first was to identify an increasing duration of infections with time, taking into account other factors associated with increasing infection risk. The second was to highlight different patterns in the effects of certain factors on new and persistent trypanosome infections.

Age Factors↗

PubMed1993

Metabolic predictors of obesity: cross-sectional versus longitudinal data.

In prospective studies in Pima Indians, four metabolic parameters, which are known to have a familial component, have been found to predict weight gain. These are: (i) low relative resting metabolic rate (RMR, relative to the average predicted rate for body size), (ii) low level of spontaneous physical activity (SPA), (iii) high 24 h respiratory quotient (RQ) and (iv) high insulin sensitivity (IS). Cross-sectional studies show that all four parameters correlate with body size: RMR vs. fat-free mass (FFM), r = 0.87, P < 0.0001; energy cost of SPA vs. weight, r = 0.69, P < 0.001; RQ vs. body fat, r = -0.23, P < 0.05; IS vs. weight, r = -0.38, P < 0.001. When these parameters are adjusted for differences in body size, then the initial value predicts the rate of change in body weight over the subsequent years: RMR (adjusted for FFM, fat mass, age and sex), r = -0.39, P < 0.001; SPA, r = -0.35, P < 0.005 (males); RQ (adjusted for fat mass), r = 0.24, P < 0.01; IS (adjusted for weight), r = 0.34, P < 0.0001. After gaining weight, the original deviation from the value predicted on the basis of the population (e.g. low relative RMR, high RQ and high IS) tends to diminish, suggesting a progressively decreasing physiological drive for further body weight gain. Thus, the high RMR, high energy cost of SPA, low RQ and low IS seen in obesity may act to limit additional weight gain.

Basal Metabolism↗

PubMedDate not supplied

Temporal relations between unexplained fatigue and depression: longitudinal data from an international study in primary care.

OBJECTIVE: Unexplained fatigue syndromes, such as chronic fatigue syndrome and neurasthenia, are strongly associated with depression, but the temporal nature of this association is not clear. METHODS: The authors examined this issue by using data from the World Health Organization collaborative study of psychological problems in general health care. Three thousand two hundred one subjects from 15 primary care centers in 14 countries were followed up for 12 months. The Composite International Diagnostic Interview was the main instrument used. Odds ratios and their 95% confidence intervals (CI) were calculated using logistic regression models adjusted for sociodemographic variables, physical morbidity and intercenter variability. RESULTS: Cases of depression were found to have an increased risk of developing a new episode of unexplained fatigue at follow-up with an adjusted odds ratio of 4.15 (95% CI = 2.64-6.54). Similarly, cases of unexplained fatigue were found to have an increased risk of developing a new episode of depression at follow-up with an adjusted odds ratio of 2.76 (95% CI = 1.32-5.78). Further adjustment for subthreshold symptoms at baseline weakened the reported associations, especially between fatigue and development of a new episode of depression, but these remained significant. CONCLUSIONS: The findings support the view that unexplained fatigue and depression might act as independent risk factors for each other.

Adult↗