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PubMed2006

Attrition in longitudinal studies: who do you lose?

OBJECTIVE: To describe the risk factors for various types of attrition in three age cohorts of women in a longitudinal study and to discuss strategies to minimise attrition. METHODS: Analysis of survey data from the Australian Longitudinal Study on Women's Health, collected by mailed questionnaire. In 1996, the study recruited and surveyed a national random sample of 'younger' (18-23 years, n = 14,247), 'mid-age' (45-50 years, n = 13,716), and 'older' women (70-75 years, n = 12,432), and began a staggered cycle of mailed follow-up questionnaires: 1998 (mid-age), 1999 (older), 2000 (younger) and so on. Demographic, health and social risk factors for attrition were examined using multivariate analysis. RESULTS: Attrition at survey 2 was highest among younger women (32%), mainly because of participants not being contactable (21%), and lower among the older (16%) and mid-age women (10%). At survey 1, the survey 2 non-respondents were more likely to report having less education, being born in a non-English-speaking country and being a current smoker, in all cohorts, and had poorer health (mid-age and older cohort) and more difficulty managing on their income (younger and mid-age). CONCLUSION: Although the magnitude of different types of attrition was found to differ by age, there were several risk factors for attrition that remained consistent. These findings are important to inform future studies on ways to lessen or prevent systematic loss of participants. IMPLICATIONS: Recruitment and follow-up methods in longitudinal studies should be tailored to maximise retention of participants at higher risk of dropout.

Adolescent↗
PubMed2005

Assessing quality of diabetes care by measuring longitudinal changes in hemoglobin A1c in the Veterans Health Administration.

CONTEXT: A1c levels are widely used to assess quality of diabetes care provided by health care systems. Currently, cross-sectional measures are commonly used for such assessments. OBJECTIVE: To study within-patient longitudinal changes in A1c levels at Veterans Health Administration (VHA) facilities as an alternative to cross-sectional measures of quality of diabetes care. DESIGN: Longitudinal study using institutional data on individual patient A1c level over time (October 1, 1998-September 30, 2000) with time variant and invariant covariates. SETTING: One hundred and twenty-five VHA facilities nationwide, October 1, 1998-September 30, 2000. PATIENTS: Diabetic veteran users with A1c measurement performed using National Glycosylated Hemoglobin Standardization Project certified A1c lab assay methods. EXPOSURES: Characteristics unlikely to reflect quality of care, but known to influence A1c levels, demographics, and baseline illness severity. MAIN OUTCOME MEASURE: Monthly change in A1c for average patient cared for at each facility. RESULTS: The preponderance of facilities showed monthly declines in within-patient A1c over the study period (mean change of -0.0148 A1c units per month, range -0.074 to 0.042). Individual facilities varied in their monthly change, with 105 facilities showing monthly declines (70 significant at .05 level) and 20 showing monthly increases (5 significant at .05 level). Case-mix adjustment resulted in modest changes (mean change of -0.0131 case-mix adjusted A1c units per month, range -0.079 to 0.043). Facilities were ranked from worst to best, with attached 90 percent confidence intervals. Among the bottom 10 ranked facilities, four remained within the bottom decile with 90 percent confidence. CONCLUSIONS: There is substantial variation in facility-level longitudinal changes in A1c levels. We propose that evaluation of change in A1c levels over time can be used as a new measure to reflect quality of care provided to populations of individuals with chronic disease.

Aged↗
PubMed2006

Health literacy, antiretroviral adherence, and HIV-RNA suppression: a longitudinal perspective.

BACKGROUND: Low health literacy has been associated with worse adherence to antiretroviral therapy (ART) and higher HIV-RNA levels, but these relationships have not been evaluated in longitudinal analyses. METHODS: We evaluated literacy using the Rapid Estimate of Adult Literacy in Medicine (REALM) (< or = 6th grade, 7th to 8th grade, > or = 9th grade) in the HIV-Alcohol Longitudinal Cohort study of HIV-infected persons with a history of alcohol problems, conducted from 1997 to 2001. We tested HIV-RNA levels and administered a standardized questionnaire regarding demographics, substance use, receipt of ART, and adherence with ART, every 6 months for up to 7 occasions. Among the 235 subjects on ART, we investigated the relationship between literacy and 2 outcomes: 100% 3-day self-reported adherence and HIV-RNA suppression (<500 copies). RESULTS: Subjects' literacy levels were the following: 14% < or = 6th grade, 29% 7th to 8th grade, and 57% > or = 9th grade. In 66% of the observations (478/725), subjects reported 100% 3-day adherence with ART. Of the 685 HIV-RNA assays from these subjects, 62% had <500 copies. In unadjusted analyses, subjects with the lowest literacy level (< or = 6th grade) had a higher odds of adherence (odds ratio [OR] 2.23, 95% confidence interval 1.15 to 4.30) and HIV-RNA suppression (OR 2.01, 95% confidence interval 1.03 to 3.90) compared with those with > or = 9th grade literacy. This trend persisted but was no longer statistically significant in adjusted models of adherence (AOR 1.93, 95% confidence interval 0.86 to 4.31) and HIV-RNA suppression (AOR 1.70, 95% confidence interval 0.79 to 3.65). CONCLUSION: Contrary to our hypothesis, low literacy was not associated with a lower odds of adherence or virologic suppression in this longitudinal analysis of HIV-infected patients with a history of alcohol problems. Indeed, trends in these data suggest the possibility that low literacy may be associated with a higher odds of adherence and virologic suppression. These counterintuitive findings underscore the need to pursue a fuller understanding of the mechanisms by which literacy affects health outcomes.

Adult↗
PubMed2006

Impact of health literacy on longitudinal asthma outcomes.

BACKGROUND: The impact of health literacy on longitudinal asthma outcomes is not known. OBJECTIVES: To measure the association between health literacy and asthma outcomes and to assess how health literacy affects outcomes through covariates. DESIGN: Longitudinal cohort. PATIENTS: One hundred and seventy-five adult asthma patients. MEASUREMENTS: Independent variables measured at enrollment included demographic and asthma characteristics, depressive symptoms, self-efficacy, and asthma knowledge. Health literacy was measured with the Test of Functional Health Literacy in Adults. Outcomes were Asthma Quality of Life Questionnaire and SF-36 scores and emergency department utilization for asthma measured every 3 to 6 months for 2 years. The effects of health literacy on outcomes and interactions between health literacy and covariates were measured with multivariable models. RESULTS: The mean age of study participants was 42 years, and 83% were women. Less health literacy was associated with worse quality of life, worse physical function, and more emergency department utilization for asthma over 2 years (P< or = .05 for all comparisons). In multivariable analysis, health literacy did not remain statistically significant with any of the outcomes. Although the magnitude of its effect on emergency department utilization remained relatively intact, its effects on quality of life and functional status became attenuated with the sequential addition of covariates, particularly asthma knowledge. CONCLUSIONS: Less health literacy was associated with poor longitudinal asthma outcomes. This relationship was both direct and indirect through effects on other independent variables, particularly patients' knowledge of asthma and self-management. Efforts to improve asthma outcomes should focus on improving literacy skills that are required to learn, understand, and implement effective self-management.

Adult↗
PubMed2004

The longitudinal occurrence and impact of comorbid chronic pain and chronic depression over two years in continuing care retirement community residents.

OBJECTIVE: To describe the longitudinal course of depressive symptoms and pain experienced by continuing care retirement community (CCRC) residents and to investigate the impact of comorbid chronic activity-limiting pain and chronic high depressive symptoms on physical functioning and health service use. METHODS: This longitudinal study of 169 CCRC residents involved five assessments (baseline and four in-person interviews at 6-month intervals). The Geriatric Depression Scale (GDS), questions drawn from the McGill Pain Questionnaire, and self-report data on physical functioning and health care use were assessed. Individuals reporting activity-limiting pain and those with GDS scores > or =11 at three or more assessments were considered to have chronic pain or chronic depression, respectively. The analysis sample included 169 CCRC residents. Multivariate logistic regression was used to test hypotheses. RESULTS: Pain and depressive symptoms were characterized by longitudinal stability. Of the sample, 37% met the criteria for chronic activity-limiting pain, 21% met the criteria for chronic high depressive symptoms, and 13% were comorbid. Adjusting for age and health conditions, those with chronic activity-limiting pain were five times more likely than those in the lowest pain group to persistently be in the worst two quartiles of physical functioning, as were those with even one GDS score >5. The odds of poor physical functioning were 11.2 times greater in those with comorbid chronic pain and depression. Comparable greater odds were seen in this sample for frequency of medical care visits (adjusted odds ratio AOR]=12.4) and consistently high use of all medical services (AOR=3.5). CONCLUSIONS: Pain and depressive symptoms were both common and appeared remarkably stable over time. Depressive symptoms contributed significantly to the prediction of impairment associated with pain, and identification and treatment of such symptoms, even minor symptoms, could reduce pain-related impairment and health care costs in the elderly.

Activities of Daily Living↗
PubMed2005

Prognostic factors for the surgery for mesial temporal lobe epilepsy: longitudinal analysis.

PURPOSE: Determining long-term prognostic factors of surgery for mesial temporal lobe epilepsy (MTLE) is important for identifying ideal candidates and predicting the prognosis for individual patients. We tried to identify the prognostic factors of anterior temporal lobectomy (ATL) for MTLE with longitudinal multivariate analysis. METHODS: Two hundred twenty-seven patients with MTLE were included in this study. The primary outcome variable was patient status 1-5 years after surgery: seizure free, or not. Clinical characteristics and recent diagnostic modalities were considered as prognostic factors. Univariate and standard multiple logistic-regression analysis for outcome at 1 and 5 years after surgery and the generalized estimation equation (GEE) model for longitudinal multiple logistic regression of the 5-year follow-up period were used. RESULTS: The seizure-free rate at 1 year was 81.1% and decreased to 75.2% at 5 years after surgery. By the univariate or standard multiple logistic-regression analysis, age at surgery or hippocampal sclerosis on magnetic resonance imaging (MRI) ipsilateral to surgery was significant for the postsurgical outcome. However, the longitudinal analysis by the GEE model revealed that younger age at surgery [odds ratio (OR), 0.59; 95% confidence interval (CI), 0.43-0.81], absence of secondarily generalized tonic-clonic seizure (2 degrees GTCS; OR, 0.45; 95% CI, 0.26-0.79), and hippocampal sclerosis on MRI (OR, 2.44; 95% CI, 1.11-5.26) were significant predictors of a good surgical outcome. CONCLUSIONS: Age at surgery, presence of 2 degrees GTCS, and hippocampal sclerosis on MRI are independent prognostic factors for ATL in MTLE. These findings suggest that MTLE is a progressive disorder, and surgical outcome is better when early ATL is performed.

Adolescent↗
PubMed2006

Longitudinal brain magnetic resonance imaging study of the alcohol-preferring rat. Part I: adult brain growth.

BACKGROUND: The alcohol-preferring (P) rat, a Wistar strain selectively bred to consume large amounts of alcohol voluntarily, has been used as an animal model of human alcoholism for 3 decades. Heretofore, knowledge about brain morphology has been confined to postmortem examination. Quantitative neuroimaging procedures make it feasible to examine the potential longitudinal effects of alcohol exposure in vivo, while controlling modifying factors, such as age, nutrition, and exercise. To date, few imaging studies have considered what morphological changes occur with age in the rodent brain, and none has systematically applied quantitative neuroimaging approaches to measure volume changes in regional brain structures over extended periods in the adult rat. METHODS: We used structural magnetic resonance imaging (MRI) in a longitudinal design to examine 2 cohorts of adult P rats, never exposed to alcohol: Cohort A included 8 rats, 7 of which survived the entire study (578 days) and 4 MRI sessions; Cohort B included 9 rats, all of which survived the study (452 days) and 5 MRI sessions. RESULTS: Growth in whole-brain volume reached maximal levels by about 450 days of age, whereas body weight continued its gain without asymptote. Growth was not uniform across the brain structures measured. Over the initial 12 months of the study, the corpus callosum area expanded 36%, cerebellum 17%, and hippocampus 10%, whereas ventricle size was unchanged. Factors affecting growth rate estimates included litter effects, MR image signal-to-noise ratio, and measurement error. CONCLUSION: Unlike longitudinal human reports of regional volume declines in aging brain tissue, several brain structures in adult rats continued growing, and some growth patterns were litter-dependent. Determining normal regional growth patterns of brain and of the substantial variance exerted by litter differences, even in selectively bred rats, is essential for establishing baselines against which normal and aberrant dynamic changes can be detected in animal models of aging and disease.

Aging↗
PubMed1997

Noncognitive disturbances in Alzheimer's disease: frequency, longitudinal course, and relationship to cognitive symptoms.

OBJECTIVE: To investigate the frequency and longitudinal course of symptoms of depression, agitation, and psychosis in a longitudinally studied sample of patients with Alzheimer's disease (AD). DESIGN: Longitudinal study of AD patients with follow-up assessments at 6-month intervals for an average of more than 3 years. SETTING: Alzheimer's Disease Research Center of the Mount Sinai Medical Center and the Bronx VA Medical Center, New York. PARTICIPANTS: A total of 153 AD patients. MEASUREMENTS: Blessed Test of Information, Memory and Concentration (BIMC) and the Alzheimer's Disease Assessment Scale cognitive (ADAS-Cog) and noncognitive (ADAS-NC) subscales. RESULTS: At entry into the study, more than 90% of patients had a behavioral disturbance that was rated as mild or worse on one of the 10 ADAS noncognitive items; and 40% had at least one rating that was moderate or severe. Correlational analyses indicated that, with the exception of the two mood-related items, noncognitive symptoms on the ADAS were not highly correlated with one another. Only one of the noncognitive items, concentration, was strongly correlated with the severity of cognitive impairment. On average, patients showed progressively worse cognitive functioning over time as measured both by the ADAS-Cog and the BIMC. The mean severity of noncognitive symptoms did not change during the course of a 5-year follow up. The severity of behavioral disturbance at any one evaluation was negatively correlated with change in behavior during the next 6 months and was not correlated with cognitive decline. CONCLUSION: Mild behavioral disturbances are common, whereas moderate to severe behavioral symptoms are less frequent in this population of AD patients. Disturbances in mood and manifestations of agitation and psychotic symptoms are not closely related to one another and show little progressive worsening over time. Rather, they tend to be episodic such that increasing severity at one time is usually followed by improvement later. Concentration problems are a manifestation of cognitive dysfunction rather than behavioral disturbance in AD. Implications of these results for treatment of noncognitive disturbances in AD are discussed.

Activities of Daily Living↗
PubMed1997

Longitudinal weight changes, length of survival, and energy requirements of long-term care residents with dementia.

OBJECTIVE: We hypothesized that institutionalized patients with dementia, who frequently have feeding problems and require supervised and assisted feeding, would lose more weight during their residency than nondemented, independently functioning residents and have compromised survival. To test this hypothesis, we examined the survival and longitudinal changes in weight of two cohorts of institutionalized residents with dementia and compared these cohorts with a cohort of nondemented residents. We also measured the resting energy expenditures of a subset of the subjects with dementia as an indicator of their energy needs. DESIGN: A longitudinal cohort study with retrospective baseline chart review and subsequent follow-up of monthly weights and mortality over 4 years. SETTING: A 725-bed long-term care institution with specified levels of care. SUBJECTS: Two cohorts of residents with dementia, one consisting of subjects who required total care throughout their institutional stay (n = 31) and another group who did not initially require total care (n = 48); these were compared with a cohort with normal mentation who were functionally independent in their daily activities (n = 26). The total number of subjects was 105. MEASUREMENTS: Demographics, medical problems, and medications by chart review; functional and mental status evaluations; longitudinal monthly weights and mortality for the 48-month study period; and resting energy expenditures by indirect calorimetry. MAIN RESULTS: Residents with dementia had lower weights on admission and throughout their stay than nondemented, independently functioning residents, and they were more likely to have a weight loss of 10 lbs or more at some point during the 4-year study period. However, their mean weights did not change during the study period. The mean survival from admission of those demented residents who died was more than 3 years. Resting energy expenditures of women residents with advanced dementia were 12% lower than predicted from the Harris Benedict equations. CONCLUSION: Dementia is not necessarily associated with unremitting weight loss during institutionalization despite the frequent occurrence of feeding difficulties and temporary weight loss. This may be caused partly by the lower than expected resting energy expenditures and, hence, energy needs of affected residents as their dementia progresses. Demented residents weighed significantly less than nondemented, independently functioning residents throughout their institutional stay. Nevertheless, nursing staff are able to maintain weight and survival for extended periods even in very impaired residents.

Activities of Daily Living↗
PubMed1997

Predictors of perceived health in hospitalized older persons: a cross-sectional and longitudinal study.

OBJECTIVES: To identify the predictors of perceived health and predictors of changes in perceived health in frail hospitalized older persons during the year after hospitalization. DESIGN: Both cross-sectional and longitudinal multivariate analysis of data from a cohort followed for 1 year. SETTING: Six hospital in a group practice model health maintenance organization (HMO) in Southern California. PARTICIPANTS: A total of 1889 persons aged 65 or older who met at least one of 13 inclusionary criteria for a randomized trial of Comprehensive Geriatric Assessment consultation at admission and completed three Functional and Health Status Questionnaires (FHSQ) during a 12-month period. MEASUREMENTS: Functional and health status measures included basic and intermediate activities of daily living (BADL and IADI) and social activities (SA) scales from the Functional Status Questionnaire as well as the mental health index (MHI) and current health perception (CHP), scales from the Medical Outcomes Study short from. Subject's severity of disease was measured by the Resource Demand Scale (RD Scale). RESULTS: In the cross-sectional analyses, MHI score, IADL score, RD Scale, history of falls during the 3 months before hospitalization, and female gender were significant predictors of perceived health in all models for each time point, BADL score, age, presence of incontinence, and ethnicity were significant in the model for baseline only, and SA score was significant in models for 3 months and 12 months only. In the longitudinal analyses, the baseline CHP score and the changes in MHI, IADL, and BADL score predicted CHP change from 0 to 3 months and from 3 to 12 months. CONCLUSIONS: Functional and psychosocial health indicators are the most important and most consistent predictors of perceived health. Our study showed that several predictors of perceived health in cross-sectional analysis did not predict changes in perceived health over a 1-year period. Hence, to fully understand the medical and social contributors to perceived health, a comprehensive approach using both cross-sectional and longitudinal analyses is necessary.

Activities of Daily Living↗
PubMed2004

Self-reported alcohol consumption and falls in older adults: cross-sectional and longitudinal analyses of the cardiovascular health study.

OBJECTIVES: To assess the cross-sectional and longitudinal associations between alcohol consumption and risk of falls in older adults. DESIGN: Cross-sectional and longitudinal analyses. SETTING: Four U.S. communities. PARTICIPANTS: A total of 5,841 older adults enrolled in the Cardiovascular Health Study, an ongoing, population-based, prospective cohort study, participated. MEASUREMENTS: Self-reported alcohol consumption at baseline, self-reported frequent falls at baseline, and the 4-year risk of falls of participants who denied frequent falls at baseline. RESULTS: Cross-sectional analysis indicated an apparent inverse association between alcohol consumption and risk of frequent falls (adjusted odds ratio in consumers of 14 or more drinks per week=0.41; 95% confidence interval (CI)=0.14-1.17; P for trend=.06), but longitudinal analysis indicated a similar 4-year risk of falls in abstainers and light to moderate drinkers but a 25% higher risk in consumers of 14 or more drinks per week (95% CI=3-52%; P for trend=.07). Similar results were found in analyses stratified by age, sex, race, and physical activity. CONCLUSION: Consumption of 14 or more drinks per week is associated with an increased risk of subsequent falls in older adults. Cross-sectional studies may fail to identify this risk of heavier drinking, perhaps because older adults at risk for falls decrease their alcohol use over time or because heavier drinkers at risk for falls tend not to enroll in cohort studies. However, because this study relied upon annual reporting of falls, further prospective studies should be conducted to confirm these findings.

Accidental Falls↗
PubMed2005

Partly conditional survival models for longitudinal data.

It is common in longitudinal studies to collect information on the time until a key clinical event, such as death, and to measure markers of patient health at multiple follow-up times. One approach to the joint analysis of survival and repeated measures data adopts a time-varying covariate regression model for the event time hazard. Using this standard approach, the instantaneous risk of death at time t is specified as a possibly semi-parametric function of covariate information that has accrued through time t. In this manuscript, we decouple the time scale for modeling the hazard from the time scale for accrual of available longitudinal covariate information. Specifically, we propose a class of models that condition on the covariate information through time s and then specifies the conditional hazard for times t, where t > s. Our approach parallels the "partly conditional" models proposed by Pepe and Couper (1997, Journal of the American Statistical Association 92, 991-998) for pure repeated measures applications. Estimation is based on the use of estimating equations applied to clusters of data formed through the creation of derived survival times that measure the time from measurement of covariates to the end of follow-up. Patient follow-up may be terminated either by the occurrence of the event or by censoring. The proposed methods allow a flexible characterization of the association between a longitudinal covariate process and a survival time, and facilitate the direct prediction of survival probabilities in the time-varying covariate setting.

Acquired Immunodeficiency Syndrome↗
PubMed2005

Time-varying functional regression for predicting remaining lifetime distributions from longitudinal trajectories.

A recurring objective in longitudinal studies on aging and longevity has been the investigation of the relationship between age-at-death and current values of a longitudinal covariate trajectory that quantifies reproductive or other behavioral activity. We propose a novel technique for predicting age-at-death distributions for situations where an entire covariate history is included in the predictor. The predictor trajectories up to current time are represented by time-varying functional principal component scores, which are continuously updated as time progresses and are considered to be time-varying predictor variables that are entered into a class of time-varying functional regression models that we propose. We demonstrate for biodemographic data how these methods can be applied to obtain predictions for age-at-death and estimates of remaining lifetime distributions, including estimates of quantiles and of prediction intervals for remaining lifetime. Estimates and predictions are obtained for individual subjects, based on their observed behavioral trajectories, and include a dimension-reduction step that is implemented by projecting on a single index. The proposed techniques are illustrated with data on longitudinal daily egg-laying for female medflies, predicting remaining lifetime and age-at-death distributions from individual event histories observed up to current time.

Animals↗
PubMed2006

Joint models for multivariate longitudinal and multivariate survival data.

Joint modeling of longitudinal and survival data is becoming increasingly essential in most cancer and AIDS clinical trials. We propose a likelihood approach to extend both longitudinal and survival components to be multidimensional. A multivariate mixed effects model is presented to explicitly capture two different sources of dependence among longitudinal measures over time as well as dependence between different variables. For the survival component of the joint model, we introduce a shared frailty, which is assumed to have a positive stable distribution, to induce correlation between failure times. The proposed marginal univariate survival model, which accommodates both zero and nonzero cure fractions for the time to event, is then applied to each marginal survival function. The proposed multivariate survival model has a proportional hazards structure for the population hazard, conditionally as well as marginally, when the baseline covariates are specified through a specific mechanism. In addition, the model is capable of dealing with survival functions with different cure rate structures. The methodology is specifically applied to the International Breast Cancer Study Group (IBCSG) trial to investigate the relationship between quality of life, disease-free survival, and overall survival.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Quadratic inference functions for varying-coefficient models with longitudinal data.

Nonparametric smoothing methods are used to model longitudinal data, but the challenge remains to incorporate correlation into nonparametric estimation procedures. In this article, we propose an efficient estimation procedure for varying-coefficient models for longitudinal data. The proposed procedure can easily take into account correlation within subjects and deal directly with both continuous and discrete response longitudinal data under the framework of generalized linear models. The proposed approach yields a more efficient estimator than the generalized estimation equation approach when the working correlation is misspecified. For varying-coefficient models, it is often of interest to test whether coefficient functions are time varying or time invariant. We propose a unified and efficient nonparametric hypothesis testing procedure, and further demonstrate that the resulting test statistics have an asymptotic chi-squared distribution. In addition, the goodness-of-fit test is applied to test whether the model assumption is satisfied. The corresponding test is also useful for choosing basis functions and the number of knots for regression spline models in conjunction with the model selection criterion. We evaluate the finite sample performance of the proposed procedures with Monte Carlo simulation studies. The proposed methodology is illustrated by the analysis of an acquired immune deficiency syndrome (AIDS) data set.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Joint modeling of survival and longitudinal data: likelihood approach revisited.

The maximum likelihood approach to jointly model the survival time and its longitudinal covariates has been successful to model both processes in longitudinal studies. Random effects in the longitudinal process are often used to model the survival times through a proportional hazards model, and this invokes an EM algorithm to search for the maximum likelihood estimates (MLEs). Several intriguing issues are examined here, including the robustness of the MLEs against departure from the normal random effects assumption, and difficulties with the profile likelihood approach to provide reliable estimates for the standard error of the MLEs. We provide insights into the robustness property and suggest to overcome the difficulty of reliable estimates for the standard errors by using bootstrap procedures. Numerical studies and data analysis illustrate our points.

Algorithms↗
PubMed1986

Design and analysis considerations for a longitudinal study of periodontal disease.

Perception and concern for the health changes in our aging population led the Veterans Administration to initiate an interdisciplinary and longitudinal investigation of the aging process, the Veterans Administration Normative Aging Study, in 1963. A cohort of the 2,280 healthy men of this study self-selected to enroll in the dental longitudinal study, an investigation of oral health in these healthy males. In 1968, 1,221 men between the ages of 25 and 75 began with a baseline cycle of 5 general series of examinations, including an interim health history and survey of dietary habits; masticatory performance and taste thresholds; salivary analyses; oral cytologic and radiographic survey and comprehensive clinical data on caries and periodontal status. Design considerations for the Dental Longitudinal Study included prospective planning of specific oral variables to be recorded, and provision of collection techniques to allow for additional analyses based on a wide menu of retrospective data. The volunteer cohort was screened to obtain men who met stringent general health criteria, who represented wide socioeconomic ranges and would likely remain geographically stable. Importantly, enrollment in the parent study was without regard for dental status or oral health. Administrative design considerations included orderly transfer for exam data to machine-readable format by use of optical scan forms designed to register specific oral variables, with security preserved for the primary source records and rapid record retrieval. Additional data collection requiring manual coding was designed to transfer spreadsheets of clinical impressions and diagnoses to computer retrieval protocols. Provisions for recording of exceptional circumstances, i.e., salient oral pathology, were recognized and the optical scan forms modified to index and retrieve such cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Periodontal conditions of adult regular dental care attendants. A 12-year longitudinal study.

The purpose of the present study was to examine longitudinal alterations in the periodontal conditions of regular dental care attendants. 225 randomly selected patients (age 18-65 years) at 12 community dental clinics in the county of Värmland, Sweden, were subjected to a baseline clinical and radiographic examination in 1978 and to a re-examination in 1990. During the study period, all participants received preventive and therapeutic measures according to decisions made by the dentist on duty in the clinics. The examinations involved assessments of number of remaining teeth, plaque, gingivitis, probing pocket depth, loss of probing attachment and periodontal bone height. The results showed that during the 12 years of monitoring, an average of 0.4 teeth were lost. The % of tooth sites with gingivitis was lower in 1990 (4%) than in 1978 (15%), but no major changes were found for the mean probing pocket depth. The mean probing attachment loss during the 12 years amounted to 0.5 mm. The tooth site analysis revealed that buccal sites had experienced more loss of attachment than lingual and approximal surfaces. Whereas no differences were observed between age groups with respect to longitudinal loss of attachment at lingual and approximal tooth sites, the youngest age group demonstrated more pronounced loss at buccal surfaces than older subjects. The radiographic assessments of the alveolar bone height revealed a mean longitudinal loss amounting to 0.2-0.4 mm in the various age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗