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PubMed1993

Changes in condom use by gay men.

Cross sectional and longitudinal data on condom use among homosexually active men is presented. Data pertain to two waves of interviewing (1987/8 and 1991) from Project SIGMA, a large longitudinal study of male homosexual behaviour in the light of HIV. Aggregate changes across the time-period indicate an increase in condom use for both insertive and receptive anal intercourse, particularly with casual partners. Condom use is still much more prevalent with casual rather than regular partners. Longitudinal analysis show considerable changes at the individual level, with almost a third of men changing their practices. Half of those decreased their risk behaviours, whilst the other half increased them. Less than 1% used condoms for fellatio in the year preceding the 1991 interview, but 8.3% had used other barriers during sex, primarily for hygiene and fun reasons, rather than as disease prophylaxis. Some implications are drawn for condom promotion and HIV prevention.

Adolescent↗

PubMed1997

Peak expiratory flow from maximum expiratory flow volume curves in a community population: cross-sectional and longitudinal analyses.

The data from a longitudinal population study in Tucson, Arizona, were used to describe the development and decline with age of the peak expiratory flows (PEF) from maximum expiratory flow-volume (MEFV) curves derived using a computer-linked pneumotachometer. Subjects had performed at least one technically acceptable MEFV test in 9 of the first 11 surveys (1972-1989). There were 2,724 subjects with adequate MEFV curves, and thus PEF, in the first survey, but only 1315 in the 11th survey. The subjects were stratified based on responses to questionnaires into nonsmoking healthy subjects and others. The PEF were analysed cross-sectionally and longitudinally using data from the 6th-11th surveys (1979-1989). For longitudinal analysis, the reference population had 397 males with 1,153 observations, and 534 females with 1,700 observations. The resulting equations were compared, evaluating differences between the longitudinal and cross-sectional equations, and between reference and nonreference longitudinal populations. The results show that there were effort-dependent effects in absolute values of PEF, even after editing. Nevertheless, as with most MEFV measures in reference populations, PEF had an early increase in the rate of development, followed by a plateau phase, followed by a constant rate of decline. The ages at which changes in growth rates of PEF occurred differed by gender. The longitudinal data in adults showed a less steep decline with age compared to the cross-sectional data, as found previously for the other MEFV variables. Males in the nonreference group did not reach the same maximum level and had a steeper decline throughout adult life than did males in the reference group; females were similar. Asthmatics of both genders had slightly greater declines compared to the other nonreference subjects.

Adolescent↗

PubMed2003

Trends in the mortality burden associated with diabetes mellitus: a population-based study in Rochester, Minn, 1970-1994.

BACKGROUND: The prevalence of diabetes mellitus (DM) has increased markedly in recent decades, but trends in the mortality burden associated with DM are unclear. Therefore, we analyzed population-based longitudinal data to address this issue. METHODS: The community-based medical records of all Rochester residents 45 years and older who died between January 1, 1970, and December 31, 1994, were reviewed to identify those who met the standardized criteria for DM before death. Trends over successive quinquenniums were assessed for the proportion of all deaths in the community of persons with prevalent DM, for mortality rates for persons with and without DM, and for the distribution of causes of death among decedents with and without DM. RESULTS: Of 10 152 total deaths in 1970-1994, 1384 (13.6%) met the criteria for prevalent DM. Between 1970-1974 and 1990-1994, the proportion of decedents with DM increased by 48.2%. Mortality rates for persons with and without DM declined by 13.8% and 21.4%, respectively. This disparity in mortality trends was most apparent for older women and younger men. There were temporal declines in the proportion of all persons dying of cardiovascular disease, but temporal declines in persons dying of cerebrovascular disease were found only in decedents without DM. CONCLUSIONS: The mortality burden associated with DM increased significantly between 1970 and 1994, probably due to increases in DM incidence and smaller declines in mortality for persons with DM relative to those without DM. In the absence of improved DM prevention and treatment, the steady declines in mortality observed for the general population since the 1960s will likely begin to slow or even reverse.

Aged↗

PubMed2006

A copula model for repeated measurements with non-ignorable non-monotone missing outcome.

A normal copula-based selection model is proposed for continuous longitudinal data with a non-ignorable non-monotone missing-data process. The normal copula is used to combine the distribution of the outcome of interest and that of the missing-data indicators given the covariates. Parameters in the model are estimated by a pseudo-likelihood method. We first use the GEE with a logistic link to estimate the parameters associated with the marginal distribution of the missing-data indicator given the covariates, assuming that covariates are always observed. Then we estimate other parameters by inserting the estimates from the first step into the full likelihood function. A simulation study is conducted to assess the robustness of the assumed model under different missing-data processes. The proposed method is then applied to one example from a community cohort study to demonstrate its capability to reduce bias.

Aged↗

PubMed1993

PC program extending the two-stage polynomial growth curve model to allow missing data.

A stand-alone, menu-driven PC program, written in GAUSS386i, extending the analysis of one-sample longitudinal data sets satisfying the two-stage polynomial growth curve model (Ten Have et al., Am J Hum Biol, 3 (1991) 269-279) to allow missing data is described, illustrated and made available to interested readers. The method and the program are illustrated using data previously analyzed by the authors (Schneiderman and Kowalski, Am J Phys Anthropol, 67 (1985) 323-333) but with several randomly chosen data points discarded and treated as missing.

Animals↗

PubMed1989

Career satisfaction in adolescent medicine. A survey of physicians trained over a 20-year period.

National data are available on the career undertakings of those trained in adolescent medicine, but longitudinal data on actual career and job satisfaction is lacking. Forty-five physicians trained in adolescent medicine from 1965 to 1985 at a large urban teaching hospital were surveyed using the Jewitt/Greenberg Career Satisfaction Questionnaire. Thirty two (71%) responded. Twenty-one (66%) were primarily in practice, eight (25%) were in academic medicine, and three (9%) were involved in administration. Five (16%) had careers in adolescent and/or young adult health care. Thirty-one (97%) claimed to at least "like" their career, and 29 (91%) felt "satisfied." Only three (9%) desired to change their career, but 11 others (34%) stated they would if they could have an equal opportunity in a new career. Four individuals (13%) would not have chosen medicine if given another chance, and 12 (30%) would not have chosen pediatrics. Greatest satisfaction was derived from patient care activities (62%), the actual work site and job (50%), and finances (40%). Dissatisfaction resulted from too little money (34%), inadequate time (25%), administrative problems (22%), and patient-related problems (22%). A large majority (72%) desired to be acknowledged as specialists. This review of graduates from a single program provides a unique perspective on the ultimate careers of trainees. A similar review of other programs may help facilitate teaching and correct programatic deficiencies. This review also suggests that careful thought should be given to a way of properly acknowledging, as specialists, those trained in adolescent medicine.

Adolescent Medicine↗

PubMed2006

Career education: an application of latent growth curve modelling to career information-seeking behaviour of school pupils.

BACKGROUND: This study applied the theory of planned behaviour (TPB) in an attempt to predict longitudinal growth of career exploratory behaviour in school pupils. The importance of information for making considered career decisions is indicated in theories of career development and choice, career education programmes, and concepts of career maturity. AIMS: The study aimed to initially model individual and group levels of career exploratory behaviour and then to identify psychological variables that predicted such behaviour. SAMPLE: Longitudinal data from a sample of 325 adolescents (mean age 16.4 years, SD = 0.77, 45% were male) was collected at three points in time. METHOD: A latent growth curve model was specified to account for initial status and subsequent linear growth of career exploratory behaviour. Variables representing the TPB were included in the model to explain the variation in the intercept and slope factors. RESULTS: The latent growth curve model was found to be an acceptable description of the data, and indicated that there was significant individual variability in terms of the intercept and slope factors. Behavioural intention was found to be a significant predictor of the intercept factor, but not of the slope factor. CONCLUSIONS: It was concluded that the TPB remains a useful theoretical framework from which to explain career information-seeking behaviour.

Adolescent↗

PubMed2003

Methods to analyse cost data of patients who withdraw in a clinical trial setting.

BACKGROUND: Missing data resulting from premature study withdrawal are a common problem in the analysis of longitudinal data in clinical trials. To date, this subject has received little attention in the context of economic evaluations and with regard to the analysis of cost data. OBJECTIVES: To (i) demonstrate the impact of patients who drop out during the study on the outcomes of an economic evaluation, and (ii) to compare the mean and variation in costs after applying five different methods to deal with incomplete data: multiple imputation, complete cases analysis, linear extrapolation, predicted mean and hot decking. STUDY DESIGN: The study was performed using cost data collected in two randomised clinical trials comparing patients with chronic obstructive pulmonary disease receiving either tiotropium bromide or ipratropium bromide. The overall dropout rate was 17%, with the daily costs of the dropouts approximately 4 times higher than the costs of the completers. METHODS: Multiple imputation is a principled method that deals with missing observations by replacing each missing observation with a set of multiple plausible values. The variance between the resulting multiple datasets is combined with the variance between the datasets to take account of the extra uncertainty that results from missing data. The outcomes after multiple imputation were compared with the results of four naive methods to deal with missing observations: complete cases analysis, linear extrapolation, predicted mean and hot decking. All costs were expressed in 2001 euros. RESULTS: In the tiotropium bromide group, mean (standard error) costs varied from Euro 955 (137) after complete cases analysis to Euro 1298 (198) after linear extrapolation. The corresponding estimates in the ipratropium bromide group were Euro 970 (125) and Euro 1561 (244), respectively. The difference in costs between treatment groups varied from -Euro 15 (95% CI: -379 to 349) after complete cases analysis to -Euro 402 (95% CI: -883 to 79) after predicted mean, in favour of the tiotropium bromide group. The difference in costs according to the other methods varied from -Euro 263 (95% CI: -878 to 353) after linear extrapolation to -Euro 265 (95% CI: -709 to 180) after multiple imputation to -Euro 359 (95% CI: -771 to 54) after hot decking. CONCLUSION: This study showed that the method of dealing with the data of the dropouts had a large impact on the outcomes of an economic evaluation. Information about the rate of patient withdrawal and the way data of dropouts are treated is of vital importance in assessing the results of economic evaluations and should always be reported. Multiple imputation is a principled method that can be used to deal with the data of these patients.

Bronchodilator Agents↗

PubMed2006

Surprising lack of sex differences in normal cognitive aging in twins.

Sex differences in the etiology of normal cognitive functioning in aging remain largely unexplored. We conducted an investigation of genetic and environmental contributions to sex differences in level of cognitive performance and rate of decline in the Swedish Adoption/Twin Study of Aging (SATSA) (Finkel & Pedersen, 2004) data set. Behavioral genetic parameterizations of a latent growth curve model were fit to longitudinal data on 11 cognitive measures. Seven hundred and ninety-eight non-demented individuals had cognitive data across four waves of measurement covering 13 years. Participants ranged in age from 44 to 88 at first testing wave; 60% were female. Results indicated sex differences in mean performance for five cognitive measures and in rates of decline for Information and Card Rotations. Only Synonyms demonstrated sex differences in genetic and environmental contributions to mean performance: heritability was higher in men than women. Despite differential longevity and susceptibility to disease, there are no consistent indications that men and women show different patterns of cognitive aging.

Adult↗

PubMed2000

Prevalence of undiagnosed diabetes in three American Indian populations. A comparison of the 1997 American Diabetes Association diagnostic criteria and the 1985 World Health Organization diagnostic criteria: the Strong Heart Study.

OBJECTIVE: In 1997, the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus of the American Diabetes Association (ADA) recommended three new sets of criteria for the diagnosis of diabetes that were different from those established by the World Health Organization (WHO) in 1985. One of these three methods was based on a fasting plasma glucose value only. This article compares ADA criteria with WHO criteria by applying them to three subgroups of American Indians in the Strong Heart Study who had no known diabetes. RESEARCH DESIGN AND METHODS: The Strong Heart Study is a prospective epidemiological study of vascular disease in three American Indian populations aged 45-74 years. During the baseline examination from 1988 to 1991, participants without diagnosed diabetes underwent a fasting glucose test and a 2-h oral glucose tolerance test. These values were used to compare the ADA and WHO diagnostic criteria. RESULTS: By using fasting and 2-h glucose values, prevalence rates of undiagnosed diabetes were 15.9% according to WHO criteria and 14.4% according to ADA criteria. The overall agreement rate was 65%, and the weighted kappa statistic was 0.474, which indicates moderate agreement. The age-specific analysis showed that, among participants between 45 and 54 years of age, the prevalence rates of undiagnosed diabetes were 13.4% according to WHO criteria and 12.7% according to ADA criteria. Among those aged 55-74 years, the rates were 18.7% according to WHO criteria and 16.3% according to ADA criteria. Thus, the difference in the prevalence rates when using WHO and ADA criteria, although generally small in this population, was three times higher in the older group (2.4%) than the difference in the younger group (0.7%). CONCLUSIONS: The Strong Heart Study found that prevalence rates of undiagnosed diabetes determined by ADA criteria and WHO criteria were similar in its American Indian population. The data suggest that the difference between the two criteria may increase as age increases. Longitudinal data will be needed to evaluate further the utility of the two criteria.

Aged↗

PubMed1992

Adequacy of peritoneal dialysis: a review of quantitative and qualitative approaches.

This paper reviews the qualitative and quantitative approaches to assessing the adequacy of peritoneal dialysis. The quantitative measures reviewed include the KT/V urea index, the dialysis index, the weekly creatinine clearance, and the creatinine efficiency number. Studies that support as well as refute these measures are reviewed briefly. Many of these studies are retrospective analyses of longitudinal data in small numbers of patients or prospective cross-sectional studies. A prospective, longitudinal study involving large numbers of patients is required to resolve some of the controversies regarding the adequacy of peritoneal dialysis.

Creatinine↗

PubMed1990

Studies on malaria transmission in Orissa state: Part I. Development of a methodology for systematic studies.

Standardized collections of Anopheles were conducted by three Entomology Field Investigation Units (FIU's) working in three distinctively different areas of Orissa State. The FIU's conducted identical routine weekly work schedules in each of 12 mesoendemic or hyperendemic study villages every month. In addition, monthly house-to-house fever case surveys were conducted in each study village and biannual malariometric surveys were carried out with the timing being shifted, so that eventually all seasons were included. Such complete, extensive and meticulous entomological and epidemiological data have not been obtained earlier from this area. In fact, until the present longitudinal data became available, it was necessary to rely upon information which was gathered some 40 years ago, when environmental conditions were substantially different. The ensuing article describes the methodology that was employed to establish these systematic studies.

Animals↗

PubMed1997

Verb use in specific language impairment.

The aim of the present study was to use longitudinal data to provide a detailed profile of early word combinations by children with SLI. Three children with SLI were videotaped during mother-child interactions in the home over a 2-year period. The data obtained were compared to MLU-matched samples of normal language-learning children from Wells' (1981) longitudinal database, which provided a control for the linguistic measures used in this study. A range of analyses were carried out on controlled data samples in order to determine how the children with SLI's early utterances compared with those of MLU-matched normal language peers. The measures were specifically designed to assess the children's use of verbs and verb morphology because recent research has suggested that verbs may play a central role in the acquisition process, and children with SLI may have particular problems with verbs. We found that children with SLI used verbs less frequently, nouns more frequently, and were more input-dependent than their MLU-matched peers. The children with SLI used verb bare stems incorrectly more often than their MLU-matched counterparts. However, further analyses showed that this high frequency of incorrect bare stems may be at least partly due to the fact that children with SLI have particular difficulties using auxiliaries. Furthermore, the proportion of verb use that consisted of General All Purpose (GAP) verbs for children with SLI was similar to that of the MLU-matched children. The above findings were compared with those from other relevant studies of lexical diversity in children with SLI, and the potential implications of these data for theories of SLI language development were discussed, particularly with reference to Marchman and Bates' (1994) "critical mass" hypothesis.

Child Language↗

PubMed1985

Alcohol versus exercise for coronary protection.

Both alcohol and exercise have been said to protect against coronary heart disease. The epidemiologic data suggest exercise, per se, does, but alcohol, per se, does not protect against coronary heart disease. Recent longitudinal data suggest teetotalers, especially those who have never smoked, have the lowest coronary heart disease mortality of all. Other cross-sectional and longitudinal studies that suggest light drinkers have the lowest coronary heart disease mortality may be biased because: (1) the teetotalers include some ex-drinkers who may have quit drinking because of coronary heart disease; and (2) the light drinkers include some who drink very rarely, and/or drink very small amounts, and/or have a lower risk of coronary heart disease independent of alcohol because they are more health-conscious in general. The metabolic data also suggest exercise, but not alcohol, protects against coronary heart disease. Exercise increases the level of high-density lipoprotein 2, which correlates well with coronary heart disease risk; alcohol in moderation seems to increase the level of high-density lipoprotein 3, which correlates poorly with coronary heart disease risk and may merely reflect hepatic enzyme induction. Exercise and alcohol influence blood pressure, body weight, and glucose tolerance in opposite directions; in each instance, the influence of exercise is beneficial, that of alcohol detrimental, to the prevention of coronary heart disease. There seems to be no reason to use alcohol for coronary protection.

Alcohol Drinking↗

PubMed2000

Euro-Growth references on increments in length, weight, and head and arm circumferences during the first 3 years of life. Euro-Growth Study Group.

BACKGROUND: Reliable assessment of growth performance of infants and young children requires reference data increments. Available increment references are based on data fitted to mathematical models, a process that diminishes variation in increment values. METHODS: Fully longitudinal data from the multicenter Euro-Growth Study (21 study sites: n = 2145 children) were used to develop sex-specific percentiles for increments in length, weight, and head and mid-upper arm circumferences for selected intervals during the first 36 months of life. Increments (per unit of time) were calculated for 2-, 3- and 6-month intervals from birth to 12 months of age and for 6-month intervals from 12 to 36 months of age. Weight increments were also calculated for 1-month intervals from birth to 6 months of age. The influence of sex, mid-parental height, and study site was determined using analysis of covariance. Comparison with other references was accomplished using percentile values. RESULTS: Mean and standard deviation values as well as selected percentiles (P; P3, P5, P10, P25, P50, P75, P90, P95, and P97) of increments are presented. Length increments of boys were higher than those of girls until 5 months of age but tended to be lower thereafter. Weight increments of boys were higher until 9 months of age. Sex, mid-parental height, and study site explained only between 2% and 13% of the variances of increments. Mean increments were comparable but P10 and P90 substantially differed from published data. CONCLUSIONS: The new Euro-Growth references for increments in length, weight, and head and mid-upper arm circumferences provide tools for health workers that should be useful in screening for adequacy of growth during the first 3 years of life.

Age Factors↗

PubMed2005

Memory performance in polyvalent MDMA (ecstasy) users who continue or discontinue MDMA use.

BACKGROUND: The popular dance drug ecstasy (3,4-methylenedioxymethamphetamine=MDMA) is a serotonergic neurotoxin in animal studies. Several cross-sectional investigations reported low memory and learning performance in ecstasy users, particularly in those reporting heavy patterns of drug use. Since, serotonin has a recognized role in memory processes, these findings were mostly interpreted as evidence for ecstasy-related neurotoxicity in humans. However, studies with user populations and controls suffer from many inherent methodological problems. Moreover, longitudinal data on memory performance after continued or discontinued ecstasy use are scarce. METHODS: In the present longitudinal study, we examined memory performance in 38 MDMA users over the course of 18 months. RESULTS: Subjects who stopped MDMA use after the baseline examination (n=17) did not improve, and subjects who continued MDMA use (n=21) did not deteriorate in terms of test performance. CONCLUSIONS: Our data do not support, but they also do not rule out memory decline following use of the serotonergic neurotoxin MDMA. In light of the popularity of ecstasy among young people, further investigations are needed. In our view, research strategies should now move to prospective designs in order to shed more light on the course of possible adverse cognitive effects of ecstasy use.

Adult↗

PubMed2003

Estimating correlation by using a general linear mixed model: evaluation of the relationship between the concentration of HIV-1 RNA in blood and semen.

Estimating the correlation coefficient between two outcome variables is one of the most important aspects of epidemiological and clinical research. A simple Pearson's correlation coefficient method is usually employed when there are complete independent data points for both outcome variables. However, researchers often deal with correlated observations in a longitudinal setting with missing values where a simple Pearson's correlation coefficient method cannot be used. General linear mixed models (GLMM) techniques were used to estimate correlation coefficients in a longitudinal data set with missing values. A random regression mixed model with unstructured covariance matrix was employed to estimate correlation coefficients between concentrations of HIV-1 RNA in blood and seminal plasma. The effects of CD4 count and antiretroviral therapy were also examined. We used data sets from three different centres (650 samples from 238 patients) where blood and seminal plasma HIV-1 RNA concentrations were collected from patients; 137 samples from 90 different patients without antiviral therapy and 513 samples from 148 patients receiving therapy were considered for analysis. We found no significant correlation between blood and semen HIV-1 RNA concentration in the absence of antiviral therapy. However, a moderate correlation between blood and semen HIV-1 RNA was observed among subjects with lower CD4 counts receiving therapy. Our findings confirm and extend the idea that the concentrations of HIV-1 in semen often differ from the HIV-1 concentration in blood. Antiretroviral therapy administered to subjects with low CD4 counts result in sufficient concomitant reduction of HIV-1 in blood and semen so as to improve the correlation between these compartments. These results have important implications for studies related to the sexual transmission of HIV, and development of HIV prevention strategies.

Anti-HIV Agents↗

PubMed2003

Rationale, design, and methods of the systematic treatment enhancement program for bipolar disorder (STEP-BD).

The Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) was conceived in response to a National Institute of Mental Health initiative seeking a public health intervention model that could generate externally valid answers to treatment effectiveness questions related to bipolar disorder. STEP-BD, like all effectiveness research, faces many design challenges, including how to do the following: recruit a representative sample of patients for studies of readily available treatments; implement a common intervention strategy across diverse settings; determine outcomes for patients in multiple phases of illness; make provisions for testing as yet undetermined new treatments; integrate adjunctive psychosocial interventions; and avoid biases due to subject drop-out and last-observation-carried-forward data analyses. To meet these challenges, STEP-BD uses a hybrid design to collect longitudinal data as patients make transitions between naturalistic studies and randomized clinical trials. Bipolar patients of every subtype with age >/= 15 years are accessioned into a study registry. All patients receive a systematic assessment battery at entry and are treated by a psychiatrist (trained to deliver care and measure outcomes in patients with bipolar disorder) using a series of model practice procedures consistent with expert recommendations. At every follow-up visit, the treating psychiatrist completes a standardized assessment and assigns an operationalized clinical status based on DSM-IV criteria. Patients have independent evaluations at regular intervals throughout the study and remain under the care of the same treating psychiatrist while making transitions between randomized care studies and the standard care treatment pathways. This article reviews the methodology used for the selection and certification of the clinical treatment centers, training study personnel, the general approach to clinical management, and the sequential treatment strategies offered in the STEP-BD standard and randomized care pathways for bipolar depression and relapse prevention.

Bipolar Disorder↗