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Objectives: Identify characteristics distinguishing people who do and do not continue to participate in a longitudinal study and determine whether the longitudinal changes for people who continue are representative of the changes that would have occurred had longitudinal data been available from all of the initial participants., Method: Moderately large samples of returning (N = 2,082) and nonreturning (N = 1,698) participants across a wide age range (i.e., 18-97 years of age) performed a battery of cognitive tests and completed personality and mood questionnaires. Differences between the groups were examined with multiple regression analyses with age, returner status, and their interaction as predictors., Results: Compared with participants who did not return, returning participants at the initial occasion had higher levels of each cognitive ability and of certain personality characteristics (e.g., agreeableness and openness), but many of the differences were only apparent among adults older than 50 years of age. Importantly, there was no evidence that the longitudinal change for nonreturning participants would have been different from that among the participants who did return., Discussion: The phenomenon of selective attrition is more complex than often assumed, and it may not necessarily limit the generalizability of longitudinal comparisons., (© The Author 2013. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The East Asian site in the INTERGROWTH-21(st) Project was Shunyi County, Beijing, China, which is an affluent suburb of north Beijing delivering approximately 7000 women annually. The Newborn Cross-Sectional Study (NCSS) sample was drawn from two hospitals, covering >85% of births in the county. The Fetal Growth Longitudinal Study sample (FGLS) was recruited from the antenatal clinic of Shunyi Maternal & Child Health Hospital, the larger of the two institutions. Special activities to promote the study in this population included: (1) the distribution of health education materials about the importance of antenatal care and (2) the organisation of seminars by the study team to brief key stakeholders at the two hospitals about the goals of the research. One of the major challenges at this site in the early stages of the study was a reluctance to have an early ultrasound dating scan (<14(+0) weeks of gestation). This challenge was overcome after a thorough evaluation of the literature regarding the benefits of an early ultrasound scan for dating purposes, as a result of which there was a formal change in hospital policy., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

Meticulous standardisation and ongoing monitoring of adherence to measurement protocols during data collection are essential to ensure consistency and to minimise systematic error in multicentre studies. Strict ultrasound fetal biometric measurement protocols are used in the INTERGROWTH-21(st) Project so that data of the highest quality from different centres can be compared and potentially pooled. A central Ultrasound Quality Unit (USQU) has been set up to oversee this process. After initial training and standardisation, the USQU monitors the performance of all ultrasonographers involved in the project by continuously assessing the quality of the images and the consistency of the measurements produced. Ultrasonographers are identified when they exceed preset maximum allowable differences. Corrective action is then taken in the form of retraining or simply advice regarding changes in practice. This paper describes the procedures used, which can form a model for research settings involving ultrasound measurements., (© 2013 Royal College of Obstetricians and Gynaecologists.)

The primary aim of the INTERGROWTH-21(st) Project is to construct new, prescriptive standards describing optimal fetal and preterm postnatal growth. The anthropometric measurements include the head circumference, recumbent length and weight of the infants, and the stature and weight of the parents. In such a large, international, multicentre project, it is critical that all study sites follow standardised protocols to ensure maximal validity of the growth and nutrition indicators used. This paper describes, in detail, the selection of anthropometric personnel, equipment, and measurement and calibration protocols used to construct the new standards. Implementing these protocols at each study site ensures that the anthropometric data are of the highest quality to construct the international standards., (© 2013 Royal College of Obstetricians and Gynaecologists.)

INTERGROWTH-21(st) is a multicentre, multiethnic, population-based project, being conducted in eight geographical areas (Brazil, China, India, Italy, Kenya, Oman, UK and USA), with technical support from four global specialised units, to study growth, health and nutrition from early pregnancy to infancy. It aims to produce prescriptive growth standards, which conceptually extend the World Health Organization (WHO) Multicentre Growth Reference Study (MGRS) to cover fetal and newborn life. The new international standards will describe: (1) fetal growth assessed by clinical and ultrasound measures; (2) postnatal growth of term and preterm infants up to 2 years of age; and (3) the relationship between birthweight, length and head circumference, gestational age and perinatal outcomes. As the project has selected healthy cohorts with no obvious risk factors for intrauterine growth restriction, these standards will describe how all fetuses and newborns should grow, as opposed to traditional charts that describe how some have grown at a given place and time. These growth patterns will be related to morbidity and mortality to identify levels of perinatal risk. Additional aims include phenotypic characterisation of the preterm and impaired fetal growth syndromes and development of a prediction model, based on multiple ultrasound measurements, to estimate gestational age for use in pregnant women without access to early/frequent antenatal care., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

Correct estimation of gestational age is essential for any study of ultrasound biometry and for everyday clinical practice. However, inconsistency in pregnancy dating may occur through differences in measurement methods or errors during measurement. In the INTERGROWTH-21(st) Project, pregnancies are dated by the last menstrual period, provided that it is certain and associated with a regular menstrual cycle, and the gestational age by dates concurs with a first-trimester ultrasound crown-rump length (CRL) estimation. Hence, there was a need to standardise CRL measurement methodology across the study sites in this international, multicentre project to avoid systematic differences in dating. To achieve uniformity we undertook the following steps: the ultrasound technique was standardised by disseminating an illustrated, operating manual describing CRL plane landmarks and calliper application, and posters describing the correct acquisition technique were disseminated for quick reference. To ensure that all ultrasonographers understood the methodology, they forwarded a log-book to the INTERGROWTH-21(st) Ultrasound Coordinating Unit, containing the answers to a written test on the manual material and five images of a correctly acquired CRL. Interpretation of CRL was also standardised by ensuring that the same CRL regression formula was used across all study sites. These methods should minimise potential systematic errors in dating associated with pooling data from different health institutions, and represent a model for standardising CRL measurement in future studies., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

The Middle Eastern site in the INTERGROWTH-21(st) Project was Muscat, the capital city of Oman, with approximately 10,500 births per year. The sample for the Newborn Cross-Sectional Study (NCSS) was drawn from two hospitals covering 96% of the region's births. The Fetal Growth Longitudinal Study (FGLS) sample was recruited from four primary health facilities serving Khoula Hospital, using the eligibility criteria in the INTERGROWTH-21(st) protocol. Special activities to encourage participation in this population included local advocacy campaigns to encourage early antenatal booking and ultrasound dating in the population. The major challenges at the site were the recruitment of sufficient numbers of women at an early gestational age, and the timely measurement of all newborns within 12 hours of birth. Many individuals and institutions collaborated effectively over a period of several years on these studies, which required careful planning and close monitoring for their successful implementation., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

There are approximately 10,000 births per year in the county of Oxfordshire in the UK, which is one of the two European sites for the International Fetal and Newborn Growth Consortium for the 21(st) Century (INTERGROWTH-21(st) ) Project. The samples for both components of the project--the Fetal Growth Longitudinal Study (FGLS) and Newborn Cross-Sectional Study (NCSS)--were drawn from the John Radcliffe Hospital, a major university hospital with a large regional role that covers more than 75% of deliveries in the county. Special activities to encourage participation in this population included the formation of a research coalition to streamline recruitment in the Maternity Unit and the distribution of study information leaflets to women using the hospital's antenatal care service. This was a demanding project and several challenges were overcome to reach recruitment targets and to maintain high standards of data quality. Amongst the major challenges for FGLS at this study site was the level of ineligibility because of maternal age, smoking and body mass index (BMI) ≥ 30. The major challenge for the NCSS field teams was to ensure that all anthropometric data were collected before the early discharge of uncomplicated deliveries, often within 6 hours of birth. It is evident from our experience in implementing this project that, when large-scale clinical studies are meticulously planned and avoid major disruption to routine clinical care, they are well received by hospital staff and can contribute to the improvement of the overall standard of clinical care., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

The primary aim of the INTERGROWTH-21(st) Project is to construct new, prescriptive standards describing optimal fetal and preterm postnatal growth. The anthropometric measurements include the head circumference, recumbent length and weight of the infants, and the stature and weight of the parents. In such a large, international, multicentre project, it is critical that all study sites follow standardised protocols to ensure maximal validity of the growth and nutrition indicators used. This paper describes in detail the anthropometric training, standardisation and quality control procedures used to collect data for these new standards. The initial standardisation session was in Nairobi, Kenya, using newborns, which was followed by similar sessions in the eight participating study sites in Brazil, China, India, Italy, Kenya, Oman, UK and USA. The intraobserver and inter-observer technical error of measurement values for head circumference range from 0.3 to 0.4 cm, and for recumbent length from 0.3 to 0.5 cm. These standardisation protocols implemented at each study site worldwide ensure that the anthropometric data collected are of the highest quality to construct international growth standards., (© 2013 Royal College of Obstetricians and Gynaecologists.)

The Latin American site in the INTERGROWTH-21(st) Project was Pelotas, Brazil, with approximately 4000 births per year. The sample for the Newborn Cross-Sectional Study (NCSS) was drawn from four hospitals, covering 99% of births in the city. The Fetal Growth Longitudinal Study (FGLS) sample was recruited from one of the largest private ultrasound clinics in the city and 30 smaller, private, antenatal clinics serving middle to high socio-economic status women. Among this site's major challenges was the recruitment of women for FGLS from numerous different clinics. Several public relations activities were conducted to improve collaborative efforts between the research team and obstetricians, paediatricians and community leaders in Pelotas., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

A unified protocol is essential to ensure that fetal ultrasound measurements taken in multicentre research studies are accurate and reproducible. This paper describes the methodology used to take two-dimensional, ultrasound measurements in the longitudinal, fetal growth component of the INTERGROWTH-21(st) Project. These standardised methods should minimise the systematic errors associated with pooling data from different study sites. They represent a model for carrying out similar research studies in the future., (© 2013 Royal College of Obstetricians and Gynaecologists.)

The INTERGROWTH-21(st) Project data management was structured incorporating both a centralised and decentralised system for the eight study centres, which all used the same database and standardised data collection instruments, manuals and processes. Each centre was responsible for the entry and validation of their country-specific data, which were entered onto a centralised system maintained by the Data Coordinating Unit in Oxford. A comprehensive data management system was designed to handle the very large volumes of data. It contained internal validations to prevent incorrect and inconsistent values being captured, and allowed online data entry by local Data Management Units, as well as real-time management of recruitment and data collection by the Data Coordinating Unit in Oxford. To maintain data integrity, only the Data Coordinating Unit in Oxford had access to all the eight centres' data, which were continually monitored. All queries identified were raised with the relevant local data manager for verification and correction, if necessary. The system automatically logged an audit trail of all updates to the database with the date and name of the person who made the changes. These rigorous processes ensured that the data collected in the INTERGROWTH-21(st) Project were of exceptionally high quality., (© 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.)

Objective: The article describes the strategies adopted by the Brazilian Longitudinal Study for Adult Health (ELSA-Brasil) for participation and retention of subjects. This is key to ensure internal validity of longitudinal studies, and to identify, investigate, and ascertain outcomes of interest., Methods: The follow-up strategies include annual telephone contacts with new assessments and interviews every three to four years this approach aims to identify transient outcomes (reversible or not), permanent outcomes as well as complications related to the progression of major diseases--cardiovascular diseases and diabetes--to be studied., Results: Telephone interviews are designed to monitor subjects' health status and to identify potential health-related events such as hospital admissions, medical visits or pre-selected medical procedures. Subjects are also encouraged to report to the ELSA-Brasil team any new health-related events. When a potential event is identified, a thorough investigation is carried out to collect relevant information about that event from medical records. All data are blinded and reviewed and analyzed by a medical expert committee. Incident outcome ascertainment follows well-established international criteria to ensure data comparability and avoid misclassification. In addition to these strategies, the occurrence of health-related events is also investigated through linkage of secondary databases, such as national mortality and hospital admission databases., Conclusions: Accurate identification of outcomes will allow to estimating their incidence in the study cohort and to investigate the effect of the exposures studied in the ELSA-Brasil at baseline and at its subsequent waves.

The ELSA-Brasil (Estudo Longitudinal de Saúde do Adulto - Brazilian Longitudinal Study for Adult Health) is a cohort study composed of 15,105 adults followed up in order to assess the development of chronic diseases, especially diabetes and cardiovascular disease. Its size, multicenter nature and the diversity of measurements required effective and efficient mechanisms of quality assurance and control. The main quality assurance activities (those developed before data collection) were: careful selection of research instruments, centralized training and certification, pretesting and pilot studies, and preparation of operation manuals for the procedures. Quality control activities (developed during data collection and processing) were performed more intensively at the beginning, when routines had not been established yet. The main quality control activities were: periodic observation of technicians, test-retest studies, data monitoring, network of supervisors, and cross visits. Data that estimate the reliability of the obtained information attest that the quality goals have been achieved.

In an observational study, one treated subject may be matched for observed covariates to either one or several untreated controls. The common motivation for using several controls rather than one is to increase the power of a test of no effect under the doubtful assumption that matching for observed covariates suffices to remove bias from nonrandom treatment assignment. Does the choice between one or several matched controls affect the sensitivity of conclusions to violations of this doubtful assumption? With continuous responses, it is known that reducing the heterogeneity of matched pair differences reduces sensitivity to unmeasured biases, but increasing the sample size has a highly circumscribed effect on sensitivity to bias. Is the use of several controls rather than one analogous to a reduction in heterogeneity or to an increase in sample size? The issue is examined for Huber's m-statistics, including the t-test, the examination having three components: an example, asymptotic calculations using design sensitivity, and a simulation. Use of multiple controls with continuous responses yields a nontrivial reduction in sensitivity to unmeasured biases. An example looks at lead and cadmium in the blood of smokers from the 2008 National Health and Nutrition Examination Survey. A by-product of the discussion is a new result giving the design sensitivity for the permutation distribution of m-statistics., (Copyright © 2013, The International Biometric Society.)

Background: Household contact with an index case of an infectious disease is a known risk factor for infection transmission. However, such contact may be underestimated due to the dynamic nature of households, particularly in longitudinal studies. Such studies generally begin with contact defined at a single point in time ('snap-shot'), leading to contact misclassification for some individuals who actually experienced contact before and after the snapshot., Objective: To quantify contact misclassification with index cases of disease in households., Methods: Historical data of 112,026 individuals from 17,889 households from an epidemiological study on leprosy in northern Malawi were used. Individuals were interviewed in the early 1980s and followed up over 5 years. It was possible to trace whether individuals died, changed household within the area, or moved out of the area between the two surveys.Using a 10% sample of households as the starting population and parameters for demographic and household changes over 5 years, the extent of contact misclassification was estimated through a simulation model of household dynamics, which traced contact with index cases in households over time. The model thereafter compared initial contact status and 'true' contact status generated from simulations., Results: The starting population had 11,401 individuals, 52% female, and 224 (2%) leprosy index cases. Eleven percent of the households had at least one index case resident and 10% (1, 177) of non-case individuals were initial contacts. Sensitivity of initial contact status ranged from 0.52 to 0.74 and varied by age and sex. Sensitivity was low in those aged 20-29 and under 5 years but high in 5- to 14-year-olds. By gender, there were no differences among those aged under 5; females had lower sensitivity among those aged under 20 and higher for those above 30, respectively. Sensitivity was also low in simulations of long incubation periods., Conclusion: This work demonstrates the implications of changes in households on household contact-associated disease spread, particularly for long durations of follow-up and infections with long incubation periods where earlier unobserved contact is critical.

Background: Annually, some 9000 people in Switzerland suffer a first time stroke. Of these 60% are left with moderate to severe walking disability. Evidence shows that rehabilitation techniques which emphasise activity of the hemiplegic side increase ipsilesional cortical plasticity and improve functional outcomes. Canes are commonly used in gait rehabilitation although they significantly reduce hemiplegic muscle activity. We have shown that an orthosis "TheraTogs" (a corset with elasticated strapping) significantly increases hemiplegic muscle activity during gait. The aim of the present study is to investigate the long term effects on the recovery of gait, balance and social participation of gait rehabilitation with TheraTogs compared to gait rehabilitation with a cane following first time acute stroke., Methods/design: Multi-centre, single blind, randomised trial with 120 patients after first stroke. When subjects have reached Functional Ambulation Category 3 they will be randomly allocated into TheraTogs or cane group. TheraTogs will be applied to support hip extensor and abductor musculature according to a standardised procedure. Cane walking held at the level of the radial styloid of the sound wrist. Subjects will walk throughout the day with only the assigned walking aid. Standard therapy treatments and usual care will remain unchanged and documented. The intervention will continue for five weeks or until patients have reached Functional Ambulation category 5. Outcome measures will be assessed the day before begin of intervention, the day after completion, 3 months, 6 months and 2 years., Primary Outcome: Timed "up and go" test, secondary outcomes: peak surface EMG of gluteus maximus and gluteus medius, activation patterns of hemiplegic leg musculature, temporo-spatial gait parameters, hemiplegic hip kinematics in the frontal and sagittal planes, dynamic balance, daily activity measured by accelerometry, Stroke Impact Scale. Significance levels will be 5% with 95% CI's. IntentionToTreat analyses will be performed. Descriptive statistics will be presented., Discussion: This study could have significant implications for the clinical practice of gait rehabilitation after stroke, particularly the effect and appropriate use of walking aids.The results could be important for the development of clinical guidelines and for the socio-economic costs of post-stroke care., Trial Registration Number: ClinicalTrials.gov NCT01366729.

The number of life events reported by study participants is sensitive to the method of data collection and time intervals under consideration. Individual characteristics also influence reporting; respondents with poor mental health report more life events. Much current research on life events is cross-sectional. Data from a longitudinal study of women's health from 4 waves over a decade suggest that over time additional systematic biases in reporting life events occur. Inconsistency over time is due to both fall-off of reporting and telescoping. Intracategory variability and ambiguity of items, as well as respondent characteristics, also potentially contribute to response biases. Although some factors (e.g., item wording) are controllable, others (e.g., respondents' mental health) are not and must be factored into data analysis and interpretation.

Introduction: In this article, we introduce Marginal Structural Models, which yield unbiased estimates of causal effects of exposures in the presence of time-varying confounding variables that also act as mediators., Objectives: We describe estimation via inverse probability weighting; estimation may also be accomplished by g-computation (Robins in Latent Variable Modeling and Applications to Causality, Springer, New York, pp 69-117, 1997; van der Wal et al. in Stat Med 28:2325-2337, 2009) or targeted maximum likelihood (Rosenblum and van der Laan in Int J Biostat 6, 2010)., Conclusions: When both time-varying confounding and mediation are present in a longitudinal setting data, Marginal Structural Models are a useful tool that provides unbiased estimates.

This article focuses on the effects of operational differences in case ascertainment on estimates of prevalence and incidence of cognitive impairment and/or dementia of the Alzheimer type. Experience and insights are discussed by investigators from the Framingham Heart Study, the East Boston Senior Health Project, the Chicago Health and Aging Project, the Mayo Clinic Study of Aging, the Baltimore Longitudinal Study of Aging, and the Aging, Demographics, and Memory Study. There is a general consensus that the single most important factor determining prevalence estimates of Alzheimer's disease (AD) is the severity of cognitive impairment used as a threshold to define cases. Studies that require a level of cognitive impairment in which persons are unable to provide self-care will have much lower estimates than the studies aimed at identifying persons in the earliest stages of AD. There are limited autopsy data from the aforementioned epidemiological studies to address accuracy in the diagnosis of etiological subtype, namely the specification of AD alone or in combination with other types of pathology. However, other community-based cohort studies show that many persons with mild cognitive impairment and also some persons without dementia or mild cognitive impairment meet pathological criteria for AD, thereby suggesting that the number of persons who would benefit from an effective secondary prevention intervention is probably higher than the published prevalence estimates. Improved accuracy in the clinical diagnosis of AD is anticipated with the addition of molecular and structural biomarkers in the next generation of epidemiological studies., (Copyright © 2011 The Alzheimer's Association. Published by Elsevier Inc. All rights reserved.)

Objectives: Our objective was to develop and test standardized methods for collection and statistical analysis of longitudinal data on hospital antibacterial use from different countries., Methods: We collected data on monthly supply of antibiotics from pharmacies in one hospital from each of 18 European countries. We applied a standardized method to classify drugs, measure use in defined daily doses and compare the effect of using occupied bed-days (OBDs) or admissions as denominators for longitudinal analysis., Results: Antibiotic use increased in 14 (78%) hospitals and decreased in 4 hospitals. For 16 (89%) hospitals, adjustment of antibiotic use with OBDs resulted in larger changes over time than adjustment with admissions. Inclusion of all hospital clinical activity variables (admissions, length of stay and OBDs) in multivariate time series analysis identified distinct hospital groups. Nine (50%) hospitals had statistically significant changes in antibiotic use (six increasing and three decreasing) that were not explained (n = 3) or only partially explained (n = 6) by change in clinical activity. Three (17%) hospitals had no significant change in antibiotic use. In the remaining six hospitals, apparent changes in antibiotic use were largely explained by changes in clinical activity., Conclusions: This is the first study to use a standardized method for data collection and longitudinal analysis of antibiotic use in different hospitals. These data suggest that determination of changes in antibiotic exposure of hospital patients over a period of time is unreliable if only one clinical activity variable (such as OBDs) is used as the denominator. We recommend inclusion of admissions, OBDs and length of stay in statistical, time series analysis of antibiotic use. This model is also relevant to longitudinal analysis of infections in hospitals.

This article proposes the establishment of a United States-Israel Longitudinal Database for Healthy Aging and Preclinical Dementia as a prototype model for the eventual creation of an international database. It is envisioned that such a comprehensive international database, as a shared research resource, will provide the foundation for a systems approach to solve the dual public health problems of: (1) Early detection of individuals at an elevated risk of developing Alzheimer's disease, and (2) Developing interventions to delay onset of, or prevent, chronic brain disorders later in life., (Copyright © 2010. Published by Elsevier Inc.)

Six different models for assessing psychiatric impairment were applied to 188 men who had been studied prospectively for half a century. The six models were categorical DSM-III diagnosis by a senior psychiatrist; objective evidence of impairment in working and loving; relative maturity of ego mechanisms of defense; the Health Sickness Rating Scale; the Global Assessment Scale (Axis V of DSM-III-R); and a "research" scale designed to provide a consensual definition of "caseness." As a test of predictive validity of our impairment measures, assessments before the age of 50 years were used to predict psychosocial adjustment and physical health assessed 15 years later. All six models were highly intercorrelated and proved equally effective in predicting future impairment. Procedures to establish construct validity suggested that the presence of a DSM-III diagnosis was a valid categorical definition of case, and that Axis V of DSM-III-R was a valid dimensional measure of impairment.