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PubMed1992

A longitudinal analysis of factors related to survival in old age.

Data from a longitudinal study of the elderly in rural North Wales are used in an exploratory study of the relationships between very broadly defined social circumstances and longevity. A statistical modeling approach is adopted and has some nonroutine features necessitated by missing data on dates of death. A variety of demographic, socioeconomic, social network, quality-of-life, dependence, and health variables are found, individually, to be related to survival. Multivariate analysis demonstrated that many of these relationships are spurious and, in particular, there is no prima facie evidence that survival is affected by social networks or quality-of-life factors. However, socioeconomic factors emerge as important for the old elderly.

Aged↗
PubMed1989

Temporal trends of human immunodeficiency virus type 1 (HIV-1) infection among inmates entering a statewide prison system, 1985-1987.

Acquired immune deficiency syndrome (AIDS) became the leading cause of death among Maryland State prisoners in 1985. To identify the prevalence, risk factors, and temporal trends for infection with the human immunodeficiency virus type 1 (HIV-1) in the statewide prison system, excess sera were obtained from incoming male inmates during specified periods between April and June 1985, 1986, and 1987. Correctional medical personnel also provided demographic variables of age, race, offense category, sentence, jurisidiction, and an indicator of intravenous drug use. Once rendered anonymous, specimens were assayed for antibody to HIV-1, using ELISA and Western blot techniques. For data from April to June 1985, 1986, and 1987, the crude prevalence of anti-HIV-1 was 7.1, 7.7, and 7.0%, respectively. Although one-third of incoming inmates were identified as intravenous drug users (IVDUs), the drug use variable was missing for 70% of the 1985 sample, and 40% of the 1986 sample. Several strategies were used to examined temporal trends in the context of missing data. Univariate analyses suggested no substantial change over time for either HIV-1 seroprevalence or risk of infection among IVDUs.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

The Manton-Woodbury model for longitudinal data with dropouts.

Often in longitudinal studies one is not able to obtain a complete set of measurements of the variable recorded over time for each person in the study. This could be caused by some of the persons dying (or leaving the study for some other reasons) while the study is going on. If there is any concern that such missing data (which have been termed dropouts) and the variables measured over time affect each other, a model for the joint distribution is needed. For a review of several such models see Hogan and Laird (in this volume). A model of the same kind was proposed by Woodbury and Manton and developed further later on. In this model it is possible to describe the evolution of the distribution of the variable measured over time when exposed to mortality selection. In contrast to other models, this allows for an explicit description of the interaction between the variable measured over time and the time to dropout. We describe the model and propose some generalizations. The theory is illustrated by some Monte Carlo simulations.

Adult↗
PubMed1996

Effect of maternal age and parity on the risk of uteroplacental bleeding disorders in pregnancy.

OBJECTIVE: To examine the risk of placental abruption, placenta previa, and uterine bleeding of unknown etiology in relation to advanced maternal age and parity in a large, population-based study. METHODS: Data for this study were derived from the Nova Scotia Atlee perinatal provincial data base, Canada, an ongoing project on human reproduction. Women who delivered between 1980 and 1993 (n = 123,941) in the province of Nova Scotia were included in the study, with the exception of pregnancies resulting in multiple births (n = 2859) and those missing data on maternal age or parity (n = 14). Multivariable logistic regression models based on the method of generalized estimating equations were used to generate odds ratios after adjustment for multiple confounders. RESULTS: The frequency of abruption was increased slightly among younger women (relative risk [RR] 1.3, 95% confidence interval [CI] 1.0-1.7), compared with women ages 25-29 years, but there was no increase with advancing maternal age. In contrast, the risk of placenta previa increased dramatically with advancing maternal age, with women older than 40 years having a nearly ninefold greater risk than women under the age of 20, after adjustment for potential confounders, including parity. Uterine bleeding of unknown etiology was not associated with advanced maternal age, except for a slight increase among women over 40 (RR 1.3, 95% CI 1.0-1.6). The risk of placenta previa and placental abruption was increased with higher parity among younger women only, but uterine bleeding of unknown etiology was more weakly associated with higher parity. In addition, an analysis of the joint effects of age and parity on placental abruption indicated a strong parity effect for women under 30 years, whereas the risk of placenta previa increased with increasing parity up to age 35 years. Uterine bleeding of unknown etiology also indicated a parity effect that was restricted to women under 25 years. CONCLUSION: Multiparity is associated with the risk of placenta previa and, to a lesser extent, placental abruption, but not with other uterine bleeding. Increasing maternal age is associated independently with the risk of placenta previa, but not with either of the other two conditions. Finally, the increased risks of uteroplacental bleeding disorders with advanced parity among the younger women (ie, 20-25 years, parity 3+) may reflect effects of close pregnancy spacing, or confounding by unmeasured factors that characterize women who have many pregnancies at a relatively young age. Overall, the findings suggest that the three uteroplacental bleeding disorders do not share a common etiology in relation to maternal age and parity, and that placenta previa is linked to aging of the uterus and the effects of repeated pregnancies.

Abruptio Placentae↗
PubMed1993

Multi method approach to the assessment of data quality in the Finnish Medical Birth Registry.

OBJECTIVE: To assess comprehensively the validity of the data in the Finnish Medical Birth Registry (MBR) by the combined use of several controls and internal analysis of the data. DESIGN: The MBR data were individually linked to a medical record sample (n = 775) and to all perinatal death certificates in 1987. The data were also compared with annual hospital statistics. The distributions of birth weights and gestational ages were examined. SUBJECTS: All stillborn and liveborn babies registered in the MBR in 1987 (n = 59,370). SETTING: The nationwide MBR data were compared with medical records from one third of the Finnish hospitals, with statistics for all hospitals, and with nationwide cause of death registry data. MEASUREMENTS AND MAIN RESULTS: With regard to most variables, the data quality was good or satisfactory (agreement with medical records 95% or more). Allowing for minor deviations in variables with continuous scales improved the agreement rates further. Explanations could be deduced for items with poor agreement values. For most variables, the amount of missing data was less than 1%. With the exception of caesarean sections, medical procedures were registered in only 30 to 72% of the cases, and the proportion varied strongly between the hospitals. Common diagnoses (32 to 86%) and primary causes of death (59 to 78%) were also poorly recorded. CONCLUSIONS: Combined use of several control materials and internal analyses was successful in investigating the whole data content. The data in the MBR were generally valid but diagnoses and most data on medical procedures were not of sufficiently good quality.

Birth Certificates↗
PubMed1997

Exploring the effects of age of alcohol use initiation and psychosocial risk factors on subsequent alcohol misuse.

OBJECTIVE: This study examines whether the age of initiation of alcohol use mediates the effects of other variables that predict alcohol misuse among adolescents and also whether the age of initiation of alcohol use accounts for known gender differences in the severity of alcohol misuse. METHOD: Data were taken from an ethnically diverse sample of 808 (412 male) students who were recruited in grade 5 at age 10-11 and followed prospectively on an annual basis for the next 7 years to age 17-18. State-of-the-art missing data methodology was used to address nonresponse due to noninitiation of alcohol use. Structural equation modeling was used to examine hypotheses for the prediction of alcohol misuse. RESULTS: A younger age of alcohol initiation was strongly related to a higher level of alcohol misuse at age 17-18 and fully mediated the effects of parent drinking, proactive parenting, school bonding, peer alcohol initiation and ethnicity, all measured at age 10-11, and perceived harmfulness of alcohol use, measured at age 10-11 and age 11-12. However, age of alcohol initiation did not fully account for gender differences in the level of alcohol misuse at age 17-18. To further examine the role of gender, interactions between gender and school bonding, and gender and friend's alcohol initiation, were evaluated. However, neither of the interaction terms had direct effects on either age of initiation or level of alcohol-related problems. CONCLUSIONS: Most measured risk factors for alcohol misuse were mediated through age of alcohol initiation. Only gender differences in alcohol misuse at age 17-18 were not mediated by age of alcohol initiation. Variables associated with these differences require further study. The results of this study indicate the importance of prevention strategies to delay the age of initiation of alcohol use.

Adolescent↗
PubMed1995

Emergency medical transport of the elderly: a population-based study.

Patterns of utilization of emergency medical services transport (EMS) by the elderly are poorly understood. We determined population-based rates of EMS utilization by the elderly and characterized utilization patterns by age, gender, race, and reason for transport. This observational, population-based study was conducted in Forsyth County, NC, a semi-urban county served by one convalescent ambulance service and one EMS service. Using data on all 1990 EMS transports and the 1990 U.S. census data, age-, gender-, and race-specific transport rates for persons aged 60 or older were calculated. Reasons for transport and frequency of repeat users were established. After exclusion of transports because of an address outside the county, a nonhospital destination, a scheduled transport, or missing data, 4,688 transports (78% of total) remained for analysis. The overall rate of transport was 104/1,000 county residents. Transport rates increased for successively older five-year age groups, demonstrating a 5.7-fold stepwise increase from ages 60-65 to 85+ (51/1,000 to 291/1,000). There was no difference in mean age between patients who were frequent EMS users (more than three transports during the year) (n = 66) and other elderly transportees. Reasons for transport differed little between those 60 to 84 years of age and those 85 years of age and older with the exception of chest pain, cardiac arrest, and seizures, all of which were significantly more prevalent in the younger age group.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMedDate not supplied

Familial aggregation in the presence of temporal trends.

Models for assessing temporal trends in familial aggregation are described for both cross-sectional and longitudinal family data. Simultaneous linear structural equations on latent variables are used to model the dependence among family members. The coefficients of the equations are assumed to be parametric functions of time, so that quite complex temporal trends in familial aggregations can be accommodated. Variable family sizes and missing data values pose no problem as the parameters of the models are estimated via maximum likelihood techniques. One of the models is applied to systolic blood pressure data in 542 Japanese-American nuclear families. The results indicate limited evidence for temporal variation in the genetic expression, but that there is substantial temporal variation in environmental influences, which appear to peak at middle age.

Age Factors↗
PubMed2026

Suggestive genome-wide associations with inflammatory biomarkers in an admixed population, including a missense variant in the OR6K6 olfactory receptor gene associated with MCP-1.

BACKGROUND: Chronic low-grade inflammation drives cardiometabolic diseases and has a strong genetic basis. Most genome-wide association studies (GWAS) have focused on European populations, limiting knowledge of the genetic influences on inflammation in admixed populations such as those in Brazil. METHODS: This study is part of the cross-sectional ISA Capital Health Survey. It uses data from the 2015 ISA Nutrition cohort, which measured biochemical, genetic, anthropometric, and lifestyle factors in a probabilistic sample of São Paulo residents. Genomic DNA was extracted from 841 individuals. Genotyping was performed using the Axiom 2.0 Precision Medicine Research Array. After quality control and missing data exclusion, 244,338 SNPs from 638 individuals remained for GWAS-based association analysis with eight inflammatory biomarkers. Models were adjusted for sex, age, age2, overweight, and the first two principal components of ancestry. RESULTS: Most participants were male (53%) and not overweight (55%). The median age was 49, and 38% were older adults. In the genome-wide analysis of TNF-α, IL-10, IL-1β, monocyte chemoattractant protein-1 (MCP-1), and adiponectin, 12 SNPs were significantly associated, most of which were intronic. Notably, one signal mapped to the missense variant rs16841009 in the olfactory receptor gene OR6K6. This variant was associated with MCP-1, suggesting a possible involvement in inflammatory responses. CONCLUSIONS: We identified new SNPs linked to inflammatory biomarkers in a highly admixed Brazilian population, including a missense variant in an olfactory receptor gene linked to MCP-1. This association may be biologically important for inflammation and could affect the risk of cardiometabolic diseases.

Humans↗
PubMed1991

An indicator of adverse pregnancy outcome in France: not receiving maternity benefits.

STUDY OBJECTIVE: The aim was to compare the social characteristics, the pregnancy outcome, and the antenatal care of women in France who did not receive maternity benefits to women who did. These benefits (860 FF, approx 86 pounds per month) are given to every pregnant woman, starting in the second trimester. Payments are made on the condition that at least three antenatal visits are made, the first being before the end of the first trimester. DESIGN: The study involved a random sample of women who were interviewed after delivery during their stay in hospital. Data on pregnancy outcome were collected from medical records. SETTING: The study was carried out in four public maternity units in different regions of France. PARTICIPANTS: 1692 women were included in the analysis (86.8% of the selected sample). Of 257 exclusions, 40 had multiple pregnancies, 189 had missing data, and 28 did not answer the question concerning maternity benefits. MEASUREMENTS AND MAIN RESULTS: 4.3% of the women did not receive any maternity benefits. These women lived in poorer social conditions than the women who received the benefits. They had a higher preterm delivery rate, after controlling for risk factors in a logistic regression. Women without maternity benefits were characterised by a lower level of care, yet the majority began their antenatal care during the first trimester or had more than six visits. CONCLUSIONS: Not receiving maternity benefits during pregnancy is an index of an underprivileged situation and a risk factor for pregnancy outcome.

Age Factors↗
PubMed1989

A cautionary note on the use of autoregressive models in analysis of longitudinal data.

Rosner et al. presented a simple, easily implemented modelling method for retaining time order relationships in analyses of longitudinal data when successive measures are correlated. Evaluation of time order is particularly useful in epidemiologic studies concerned with exposure to potentially toxic substances and subsequent outcome, but may also have use in more traditional growth studies that relate intake to subsequent development. The analysis allows for unequally spaced measures and missing data. The estimation method permits varying numbers of observations per subject and, with measures equally spaced, one can fit the model with use of ordinary least squares regression software. We report on a potential false association that can result when both exposure and outcome are related to time. We illustrate this problem with a small scale simulation and example. We also note a more serious problem with Rosner's approach in interpreting parameters. Although the model may be useful for prediction, parameters depend on the autocorrelation and are not readily interpretable. We recommend alternative modelling strategies be used when autocorrelation of errors is suspected.

Age Factors↗
PubMed1991

Running average analysis of clinical trial ambulatory blood pressure data.

A method is presented for analyzing ambulatory blood pressure monitoring (ABPM) time series data obtained from well-controlled clinical trials. The method uses running averages based on fixed time-of-day intervals (rather than a fixed number of neighboring measurements). These "interval running averages" effectively estimate average blood pressure during the specified time intervals, adjusting for unequal spacing between measurements, embedded missing data, varying measurement times-of-day, and doses of study medication taken during ABP monitoring. Blood pressure changes from baseline may be computed using the interval running averages in order to separate treatment effects from patients' normal daily blood pressure cycles. To ensure valid estimation of treatment effects over time, study medication dosing times should be rigorously controlled in the trial design and conduct. Interval running average curves may be presented graphically, and from them summary statistics may be computed for purposes of statistical analysis. By allowing for the inherent complications of ABP data collection, the effect of antihypertensive treatment in well-controlled clinical trials can be discerned.

Ambulatory Care↗
PubMed1993

Size and power of two-sample tests of repeated measures data.

One method of using repeated measures data to compare treatment groups in a clinical trial is to summarize each subject's outcomes with a single summary statistic, and then perform a distribution-free comparison based on the resulting statistics. We examine extensions of this approach and conditions under which they retain proper size in the presence of missing data. The asymptotic relative efficiencies of several summary statistic tests are calculated to show which perform best in a variety of situations. The techniques are illustrated using data from an AIDS clinical trial.

Analysis of Variance↗
PubMed1995

Method for cohort and nested case-control studies: the prevalence, timing and effectiveness of obstetric ultrasound, Victoria 1991-1992.

The study was designed to assess the effectiveness of obstetric ultrasound in the diagnosis of congenital malformations and to establish its prevalence of use and timing. Statewide data were collected in 138 of the 141 obstetric hospitals in Victoria over a 12-month period during 1991-1992. Within the final cohort of 55,226 mothers providing responses, a nested case-control study group was formed. This group comprised 719 cases (infants born with one or more malformations potentially diagnosable at 16-20 weeks) and 703 controls (non-malformed infants). The cases for the group were extracted from the Victorian Congenital Malformations Register; controls were randomly selected from the Victorian Perinatal Data Collection Unit's database. Of the 1422 in the study group, 1328 medical records were validated in 100 hospitals. The design, method, procedure, sample and outcome are described for the cohort and nested case-control studies. At the conclusion of the study it was established that major variations between the cohort and missing data were confined to mothers less likely to have had a spontaneous vaginal delivery or to those with poor perinatal outcome. There was no significant selective loss of cases or controls in the nested case-control study group.

Case-Control Studies↗
PubMed1994

A new approach to the analysis of analgesic drug trials, illustrated with bromfenac data.

A clinical trial of an analgesic agent compares pain relief scores (ordered categorical responses) over time among groups of patients, each subject to a painful procedure and given various doses of active agent (including zero, i.e., placebo) on demand. Patients may elect to remedicate with an active agent if their pain relief is insufficient, so the sample of patients at any given time is biased toward those with better relief. Standard analyses usually (1) fill in the missing data but make no correction for so doing and (2) treat the ordered categorical variable as continuous. Both of these create problems in interpretation and inference, but the former is more serious than the latter. An alternative analysis has been recently proposed that deals with these problems. This article presents that method for a nonstatistical audience and illustrates its use on some data from the analgesic bromfenac.

Analgesics↗
PubMed1996

An application of hierarchical linear models to longitudinal studies.

Nursing researchers are increasingly interested in studying changes in patients' outcomes, such as physiologic and psychological status, across time. The most frequently used approaches, univariate repeated measures, multivariate repeated measures, and pre- and posttest differences, have restrictive assumptions and unrealistic data requirements. Therefore, a more flexible approach is needed. Hierarchical linear models (HLM) can be used to solve these problems. The advantages of HLM are (a) it describes each individual's growth trajectory and its relationship with initial status, (b) it is not restricted by unrealistic assumptions, (c) if solves the commonly observed problems of missing data, (d) it does not require fixed time intervals, and (e) it provides more precise estimation.

Analysis of Variance↗
PubMed1996

A computer program for regression analysis of ordered categorical repeated measurements.

RMORD is an easy-to-use FORTRAN program for the analysis of clustered ordinal data using the method of Stram, Wei, and Ware. This method constitutes an extension of the proportional-odds model to the situation in which groups of responses are correlated. At each measurement occasion, a proportional-odds regression model is fit to the data by maximizing the occasion-specific likelihood function. The joint asymptotic distribution of the occasion-specific regression parameter estimators is obtained along with a consistent estimator of their asymptotic covariance matrix. RMORD may be used when ordinal measurements are obtained at a common set of observation times for multiple subjects or clusters. Both missing data and covariates which vary within clusters can be accommodated. The program can be run on microcomputers, workstations, and mainframe computers. Two examples illustrating the usage and features of RMORD are provided.

Age Distribution↗
PubMed1996

Intention-to-treat analyses for incomplete repeated measures data.

In a randomized longitudinal clinical trial designed to evaluate two or more rival treatments, an intent-to-treat analysis requires inclusion of all randomized patients, regardless of whether they remain on protocol for the duration of the study. We propose a piecewise linear random effects model for analyzing longitudinal data where the multivariate outcome can depend upon time spent on treatment. The model assumes that data are available on a random sample of subjects after treatment is terminated, and allows either a pragmatic or explanatory analysis (as defined by Schwartz and Lellouch, 1967, Journal of Chronic Diseases 20, 637-648). Full maximum likelihood estimation of the model parameters is carried out using widely available statistical software for repeated measures with missing data and for nonparametric survival curve estimation. Data from a national, multicenter pediatric AIDS clinical trial are analyzed to illustrate implementation and interpretation of the model.

Acquired Immunodeficiency Syndrome↗