Retention Of Study Participants Research Articles

Structures and Strategies for Retaining an International Pediatric Cohort from Birth: Lessons from The Environmental Determinants of Diabetes in the Young (TEDDY) Study.

Retention of study participants in observational studies is essential to maintaining the representativeness of the population, minimizing selection bias, and assuring sufficient statistical power. The aim of this report is to describe the structures and strategies used to retain participants in The Environmental Determinants of Diabetes in the Young (TEDDY) Study, an observational study of children at increased genetic risk for type 1 diabetes followed in an intense protocol with frequent clinic visits from birth until age 15. A systematic review of methodologies used to retain research subjects identified four domains: barrier reduction strategies; community building strategies; follow-up/reminder strategies; and tracing strategies. Independent reviewers categorized the retention strategies implemented by the TEDDY Study into each of these domains. Strategies not fitting into any of these categories were placed into a fifth category unique to TEDDY. TEDDY identified over one hundred retention strategies used during the 15 years of follow-up; most could be categorized in these domains. Those unique to TEDDY included (1) study organization and structures to support retention; (2) efforts to meet the changing developmental needs of the TEDDY population, (3) implementation of efforts to address protocol challenges in real-time; and (4) employment of a re-engagement protocol for those who had dropped out of the study. Pediatric cohort studies should include strategies, structures, and resources addressing retention at the study's initiation. It is recommended that child and parent engagement in addition to the developmental needs of the child be an integrated focus of all strategies. Putting mechanisms in place to address protocol and retention challenges in real time would facilitate effectively addressing challenges as they arise. ClinicalTrials.gov Identifier: NCT00279318.

Feasibility randomised controlled trial of face-to-face counselling and mobile phone messages compared to usual care for smokeless tobacco cessation in Indian primary care: Project CERTAIN.

Smokeless tobacco (SLT) use in low- and middle-income countries (LMICs) has adverse health consequences. We hypothesize that it is feasible to test an intervention of mobile phone messages and face-to-face counselling session for SLT cessation in India. We conducted an exploratory, individual parallel two group, randomised controlled trial (RCT), with baseline -and end-point (three months from randomisation) assessments in urban primary health centres in Odisha, India. A total of 250 current (i.e., users in the last three months) SLT users or dual users (i.e., smokers and SLT users) were recruited to the trial (125 in each group). Participants were randomised to either routine care, face-to-face counselling, and reminder mobile messages or routine care only. The primary outcomes were to assess the feasibility of running a full RCT including recruitment, compliance, and retention. A total seven (77.8%) out of nine primary care centres took part in the trial. Out of the 315 SLT users invited to participate, 250 provided consent and were randomised [79.4% (95% CI: 74.5, 83.7)]. Out of the 250 randomised SLT users, 238 [95% (95% CI: 91.8, 97.5)] were followed up at three months (117 in the intervention group and 121 in the control group). Of the participants in the intervention group, 74 (63.8%) reported that they received the mobile messages. This exploratory trial demonstrated the feasibility of delivering and evaluating an intervention of mobile phone messages and face-to-face counselling for SLT users in Indian primary care in a full randomised trial. This study found that combining mobile messages with face-to-face counselling for smokeless tobacco users visiting primary health care settings in India is feasible in terms of recruitment of users, compliance with the intervention, and retention of study participants within the trial.The biochemically verified smokeless tobacco abstinence rate was higher in the intervention group compared with the control groupThere was poor agreement between self-reported tobacco cessation and the measured salivary cotinine in smokeless tobacco users.The findings support the feasibility and acceptability of the intervention signalling the need for a larger clinical trial to test effectiveness of the intervention.

Retaining Participants in Longitudinal Studies of Alzheimer's Disease.

Retention of study participants is essential to advancing Alzheimer's disease (AD) research and developing therapeutic interventions. However, recent multi-year AD studies have lost 10% to 54% of participants. We surveyed a random sample of 443 participants (Clinical Dementia Rating [CDR]≤1) at four Alzheimer Disease Research Centers to elucidate perceived facilitators and barriers to continued participation in longitudinal AD research. Reasons for participation were characterized with factor analysis. Effects of perceived fulfillment of one's own goals and complaints on attendance and likelihood of dropout were estimated with logistic regression models. Open-ended responses suggesting study improvements were analyzed with a Latent Dirichlet Allocation topic model. Factor analyses revealed two categories, personal benefit and altruism, as drivers of continued participation. Participants with cognitive impairment (CDR > 0) emphasized personal benefits more than societal benefits. Participants with higher trust in medical researchers were more likely to emphasize broader social benefits. A minority endorsed any complaints. Higher perceived fulfillment of one's own goals and fewer complaints were related to higher attendance and lower likelihood of dropout. Facilitators included access to medical center support and/or future treatment, learning about AD and memory concerns, and enjoying time with staff. Participants' suggestions emphasized more feedback about individual test results and AD research. The results confirmed previously identified facilitators and barriers. Two new areas, improved communication about individual test results and greater feedback about AD research, emerged as the primary factors to improve participation.

Lessons Learned Recruiting and Retaining Pregnant and Postpartum Individuals in Digital Trials: Viewpoint.

In an increasingly connected world and in the midst of a global pandemic, digital trials offer numerous advantages over traditional trials that rely on physical study sites. Digital trials have the potential to improve access to research and clinical treatments for the most vulnerable and minoritized, including pregnant and postpartum individuals. However, digital trials are underutilized in maternal and child health research, and there is limited evidence to inform the design and conduct of digital trials. Our research collaborative, consisting of 5 research teams in the U.S. and Australia, aimed to address this gap. We collaborated to share lessons learned from our experiences recruiting and retaining pregnant and postpartum individuals in digital trials of social and behavioral interventions. We first discuss the promise of digital trials in improving participation in research during the perinatal period, as well as the unique challenges they pose. Second, we present lessons learned from 12 completed and ongoing digital trials that have used platforms such as Ovia, Facebook, and Instagram for recruitment. Our trials evaluated interventions for breastfeeding, prenatal and postpartum depression, insomnia, decision making, and chronic pain. We focus on challenges and lessons learned in 3 key areas: (1) rapid recruitment of large samples with a diversity of minoritized identities, (2) retention of study participants in longitudinal studies, and (3) prevention of fraudulent enrollment. We offer concrete strategies that we pilot-tested to address these challenges. Strategies presented in this commentary can be incorporated, as well as formally evaluated, in future studies.

Keeping together: older people in longitudinal research studies, the case of TwinsUK

PurposeA decline in participation in research studies as people age is inevitable as health declines. This paper aims to address this by collecting data from a group of participants to examine their reasons for declining attendance and suggestions for maintaining attendance as participants age.Design/methodology/approachThis research used a postal self-completed questionnaire including open and closed questions. The questionnaire was sent to those participants who have declined to attend further clinic visits. Results were analysed using thematic content analysis.FindingsThe study had a 51% response rate. Participants reported difficulty with travelling to the clinic, and health as the main issues in addition to family demands and a lack of understanding regarding the continuing participation of a singleton twin.Research limitations/implicationsThis study could only include data from responding participants, answers to open question also included comments from participants regarding their twin.Practical implicationsAn anonymous questionnaire was sent to all individuals in the Keeping Together project. It was therefore not possible to identify if responses were from both members of a twin pair.Originality/valueMaintaining participation in longitudinal studies is of crucial importance to enhance the value of data. Retention of participants in studies may change as people age and health becomes impaired. Suggestions for maintaining and improving the retention of older participants have been identified and are generalisable to other longitudinal studies of ageing.

Recruitment and retention of mothers of preschoolers and school-aged children in a social media-delivered healthy eating intervention: lessons learned from a randomized controlled trial

BackgroundSocial media represent cost-effective platforms to advance the dissemination and uptake of health research to improve population health. However, there is limited evidence available to support researchers overcome methodological challenges related to recruitment and retention of participants in studies using social media for delivering behavior change interventions. This study aims to describe the recruitment and the retention strategies used in a randomized controlled trial (RCT) that evaluated a blog-delivered healthy eating intervention among mothers of preschoolers and school-aged children.MethodsEighty-four adult mothers of children aged between two and 12 years old living in Quebec City, Quebec, Canada, were recruited between October 2015 and February 2017 using traditional methods (e.g. institutional email lists, flyers, newspapers, and word of mouth) and Facebook advertisements. Retention rates were calculated at the end of the 6-month intervention and at a 12-month follow-up assessment. Sociodemographic characteristics, Internet use behaviors and retention rates of mothers recruited through traditional methods and Facebook were compared using Wilcoxon-Mann-Whitney tests and Fisher exact tests.ResultsOf the 196 mothers who responded to the recruitment call, 87 (44.4%) were eligible and 84 (42.9%) were randomized to the trial, representing a recruitment success of 76.4% (84/110) from the planned sample size target. Among those, a minority (3.6%) were recruited using Facebook. Those mothers presented similar sociodemographic characteristics to those recruited using traditional methods. Retention rates were 73.8% and 66.7% at 6 and 12 months, respectively, with similar rates between mothers recruited using Facebook and traditional methods. Various challenges associated with population retention were highlighted with lack of time being mothers’ main reason for withdrawing from the study.ConclusionsThe methodological challenges experienced during the conduct of the blog-delivered healthy eating intervention allowed to draw upon several lessons regarding the recruitment process and the retention of mothers of preschoolers and school-aged children to inform future social media-delivered research. Recommendations for future research include exploring mothers’ perceptions and preferences to tailor social media recruitment, ensure that interventions are delivered to them using social media platforms that are already integrated into their routine, and are providing remote outcome assessments to increase participant retention.Trial registrationClinical Trial Protocol NCT03156803. Registered on 17 May 2017, retrospectively registered.

Clinical Trials during Covid-19

The current novel coronavirus disease 2019 (COVID-19) pandemic has led to substantial changes in health risks, access to health care, and daily interactions. Through these and other challenges, the pandemic is affecting ongoing clinical trials that are evaluating interventions aimed at preventing or treating diseases other than COVID-19. Meaningful alterations to the implementation of protocol-specified procedures for adherence and retention of study participants, without careful consideration of the consequences to statistical analysis, can compromise the generalizability of clinical trial results about efficacy and safety of studied interventions in the postpandemic setting [1].

Tracking Assault-injured, Drug-using Youth in Longitudinal Research: Follow-up Methods.

Violence is one of the leading causes of death among youth ages 14 to 24. Hospital- and emergency department (ED)-based violence prevention programs are increasingly becoming a critical part of public health efforts; however, evaluation of prevention efforts is needed to create evidence-based best practices. Retention of study participants is key to evaluations, although little literature exists regarding optimizing follow-up methods for violently injured youth. This study aims to describe the methods for retention in youth violence studies and the characteristics of hard-to-reach participants. The Flint Youth Injury (FYI) Study is a prospective study following a cohort of assault-injured, drug-using youth recruited in an urban ED, and a comparison population of drug-using youth seeking medical or non-violence-related injury care. Validated survey instruments were administered at baseline and four follow-up time points (6, 12, 18, and 24 months). Follow-up contacts used a variety of strategies and all attempts were coded by type and level of success. Regression analysis was used to predict contact difficulty and follow-up interview completion at 24 months. A total of 599 patients (ages 14-24) were recruited from the ED (mean ± SD age = 20.1 ± 2.4 years, 41.2% female, 58.2% African American), with follow-up rates at 6, 12, 18, and 24 months of 85.3%, 83.7% 84.2%, and 85.3%, respectively. Participant contact efforts ranged from two to 53 times per follow-up time frame to complete a follow-up appointment, and more than 20% of appointments were completed off site at community locations (e.g., participants' homes, jail/prison). Participants who were younger (p < 0.05) and female (p < 0.01) were more likely to complete their 24-month follow-up interview. Participants who sought care in the ED for assault injury (p < 0.05) and had a substance use disorder (p < 0.01) at baseline required fewer contact attempts to complete their 24-month follow-up, while participants reporting a fight within the immediate 3 months before their 24-month follow-up (p < 0.01) required more intensive contact efforts. The FYI study demonstrated that achieving high follow-up rates for a difficult-to-track, violently-injured ED population is feasible through the use of established contact strategies and a variety of interview locations. Results have implications for follow-up strategies planned as part of other violence prevention studies.

Design and implementation of a factorial randomized controlled trial of methadone maintenance therapy and an evidence-based behavioral intervention for incarcerated people living with HIV and opioid dependence in Malaysia

Incarcerated people living with HIV and opioid dependence face enormous challenges to accessing evidence-based treatment during incarceration and after release into the community, placing them at risk of poor HIV treatment outcomes, relapse to opioid use and accompanying HIV transmission risk behaviors. Here we describe in detail the design and implementation of Project Harapan, a prospective clinical trial conducted among people living with HIV and opioid dependence who transitioned from prison to the community in Malaysia from 2010 to 2014. This trial involved 2 interventions: within-prison initiation of methadone maintenance therapy and an evidence-based behavioral intervention adapted to the Malaysian context (the Holistic Health Recovery Program for Malaysia, HHRP-M). Individuals were recruited and received the interventions while incarcerated and were followed for 12months after release to assess post-release HIV transmission risk behaviors and a range of other health-related outcomes. Project Harapan was designed as a fully randomized 2×2 factorial trial where individuals would be allocated in equal proportions to methadone maintenance therapy and HHRP-M, methadone maintenance therapy alone, HHRP-M alone, or control. Partway through study implementation, allocation to methadone maintenance therapy was changed from randomization to participant choice; randomization to HHRP-M continued throughout. We describe the justification for this study; the development and implementation of these interventions; changes to the protocol; and screening, enrollment, treatment receipt, and retention of study participants. Logistical, ethical, and analytic issues associated with the implementation of this study are discussed.

Mediators of Atherosclerosis in South Asians Living in America: Use of Web-Based Methods for Follow-Up and Collection of Patient-Reported Outcome Measures.

BackgroundA key challenge for longitudinal cohort studies is follow-up and retention of study participants. Participant follow-up in longitudinal cohort studies is costly and time-consuming for research staff and participants.ObjectiveThis study determined the feasibility and costs of using Web-based technologies for follow-up and collection of patient-reported outcomes in the Mediators of Atherosclerosis in South Asians Living in America (MASALA) study.MethodsThe MASALA study is a community-based cohort of 906 South Asians in the United States. Since the baseline in-person visits (2010-2013), a yearly telephone follow-up survey was used to assess participants’ health status and incidence of cardiovascular disease. A Web-based version of the follow-up survey was developed using the REDCap (Research Electronic Data Capture) Web app. Participants from the Chicago field center who were due for their annual follow-up and who had a valid email address were sent an email link to a secure online portal where they could complete the survey. Telephone follow-up was used with nonresponders.ResultsA link to the Web survey was emailed to 285 participants (February to October 2014) and the overall completion rate was 47.7% (136/285). One-third of participants who were unresponsive (n=36) to annual telephone follow-up completed the Web survey. Web responders were younger, more likely to be married, and to have higher education and income compared (P<.05) to telephone-only responders. Web survey development involved 240 hours of research staff time. Since launching, the Web-based survey has required 3 hours per week of staff time.ConclusionsAlthough electronic follow-up will not be a panacea for cohort operations, it will serve as an adjunctive strategy to telephonic follow-up for maximizing cohort retention with lower costs.

Patient responses to research recruitment and follow-up surveys: findings from a diverse multicultural health care setting in Qatar.

BackgroundHealth care researchers working in the Arabian Gulf need information on how to optimize recruitment and retention of study participants in extremely culturally diverse settings. Implemented in Doha, Qatar in 2012 with 4 language groups, namely Arabic, English, Hindi, and Urdu, this research documents persons’ responses to recruitment, consent, follow-up, and reminder procedures during psychometric testing of the Multicultural Assessment Instrument (MAI), a novel self- or interviewer-administered survey.MethodsBilingual research assistants recruited adults in outpatient clinics by approaching persons in particular who appeared to be from a target language group. Participants completed the MAI, a second acculturation instrument used for content-validity assessment, and a demographics questionnaire. Participants were asked to take the MAI again in 2–3 weeks, in person or by post, to assess test-retest reliability. Recruitment data were analyzed by using nonparametric statistics.ResultsOf 1503 persons approached during recruitment, 400 enrolled (27 %)—100 per language group. The enrollment rates in the language groups were: Arabic-32 %; English-33 %; Hindi-18 %; Urdu-30 %. The groups varied somewhat in their preferences regarding consent procedure, follow-up survey administration, contact mode for follow-up reminders, and disclosure of personal mailing address (for postal follow-up). Over all, telephone was the preferred medium for follow-up reminders. Of 64 persons who accepted a research assistant’s invitation for in-person follow-up, 40 participants completed the interview (follow-up rate, 63 %); among 126 persons in the postal group with a deliverable address, 29 participants mailed back a completed follow-up survey (response rate, 23 %).ConclusionsResearchers in the Arabian Gulf face challenges to successfully identify, enroll, and retain eligible study participants. Although bilingual assistants—often from the persons’ own culture—recruited face-to-face, and our questionnaire contained no health care-related content, many persons were reluctant to participate. This occurrence was observed especially at follow-up, particularly among participants who had agreed to follow-up by post.

Public and patient involvement in paediatric research

Public and patient involvement (PPI) in health research is a dynamic partnership between patients and/or members of the public and researchers. Involvement is distinct from being subjects of research (participation)...

Look inside Look AHEAD: why the glass is more than half-full.

Look AHEAD is the only long-term study in a large cohort of subjects with type 2 diabetes that assessed the effect of intensive lifestyle, predominantly diet and exercise, on a number of outcomes. While Look AHEAD was not able to detect a significant effect of intensive lifestyle modification on cardiovascular outcomes, it clearly demonstrated numerous beneficial and sustained effects on health outcomes that are relevant to this population. Without the exceptional retention of study participants, it would have been difficult to detect these benefits. Our review provides a perspective on aspects related to exercise, diet, and weight loss in relation to cardiovascular outcomes and potential future research.

Socio-ecological Model as a Framework for Overcoming Barriers and Challenges in Randomized Control Trials in Minority and Underserved Communities

Numerous barriers and challenges can hinder the successful enrollment and retention of study participants in clinical trials targeting minority populations. To conduct quality research, it is important to investigate these challenges, determine appropriate strategies that are evidence-based and continue seeking methods of improvement. In this paper, we report such experiences in a registered clinical trial in an underserved minority population in the Southern part of United States. This research study is a randomized double-blind controlled clinical trial that tests the efficacy of higher-strength as compared to low-strength/standard of care folic acid to prevent fetal body and brain size reduction in pregnant women who smoke. A unique approach in this socio-behavioral, genetic-epigenetic clinical trial is that we have adopted the socio-ecological model as a functional platform to effectively achieve and maintain high participant recruitment and retention rates. We highlight the barriers we have encountered in our trial and describe how we have successfully applied the socio-ecological model to overcome these obstacles. Our positive experience will be of utility to other researchers globally. Our fi ndings have far-reaching implications as the socio-ecological model approach is adaptable to developed and developing regions and has the potential to increase recruitment and retention of hard-to-reach populations who are typically under-represented in clinical trials.

Abstract IA20: The NCI Cohort Consortium: Increasing power, enhancing collaborations, advancing science.

Abstract The Cohort Consortium is an extramural-intramural partnership formed by the National Cancer Institute (NCI) to foster communication among investigators leading cohort studies of cancer; promote collaborative research projects for topics not easily addressed in a single study; and identify common challenges in cohort research and search for solutions. The Cohort Consortium includes investigators responsible for more than 40 high-quality cancer epidemiology cohorts involving more than 4 million people. The cohorts are international in scope and cover large, rich, and diverse populations. Extensive risk factor data are available on each cohort, and biospecimens, including germline DNA collected at baseline, are available on more than 2 million individuals. Investigators team up to use common protocols and methods, and to conduct coordinated parallel and pooled analyses. Some recent accomplishments include publications of genome-wide association studies of pancreatic cancer and on the effect of high body mass index on mortality after eliminating the influence of tobacco smoking and co-morbidities. The Consortium provides a forum to discuss scientific questions in cancer research that cohort studies can help address such as how metabolomics can best be examined in human population studies and how cohort studies can better address the role of physical and chemical agents on cancer risk. It also can focus attention on new methodologies such as the use of social media and new ways of interacting with cohort study participants that could enhance data collection, data quality, and study participant retention and engagement. Citation Format: Deborah M. Winn. The NCI Cohort Consortium: Increasing power, enhancing collaborations, advancing science. [abstract]. In: Proceedings of the AACR Special Conference on Post-GWAS Horizons in Molecular Epidemiology: Digging Deeper into the Environment; 2012 Nov 11-14; Hollywood, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(11 Suppl):Abstract nr IA20.

Recruitment and Retention of Older Adolescent and Young Adult Female Survivors of Childhood Cancer in Longitudinal Research

To describe the challenges encountered in the recruitment and retention of a sample of older adolescent and young adult female survivors of childhood cancer for a longitudinal study testing a targeted psychosocial intervention aimed at enhancing hope. Published literature on constructing longitudinal intervention studies and strategies in the recruitment and retention of childhood cancer survivors in research was used to develop the protocol of this study. Using empirical literature to construct the study's design resulted in achieving certain goals for the design, but not in the recruitment and retention of study participants. Using online technology to deliver the intervention and collect data was efficient and effective. Traditional approaches to recruitment and retention of those survivors, however, were not effective. Use of more novel approaches to enroll study participants demonstrated only modest success. Additional research is needed on strategies to successfully recruit and retain older adolescents and young adult female survivors of childhood cancer in longitudinal intervention studies. The improvement in the psychological well-being of female survivors of childhood cancer remains an important outcome in ongoing care. The need to continue to identify creative and effective ways to recruit and retain those survivors is warranted.

Lost in translation: will the ‘personal’ become ‘impersonal’ when conducting research in the age of technology?

As new technology permeates the research process, could the personal touch be lost in translation? When conducting research, its success is dependent upon the relationships established between the investigator, their research team and the study participants. Penckofer, Byrn, Mumby and Ferrans identify factors often associated with successful recruitment and retention of study participants, including advertising through branding, monetary incentives, convenient times and the altruistic nature of individuals [1]. They emphasize, however, that the single most important factor in subject accrual and participation is the relationship(s) the participant establishes with the study personnel during their research experience. Using ‘Peplau’s Theory of Interpersonal Relations’, they address the three phases of the relationship that develop as the study participant engages in the research process [2]. The first phase called the ‘orientation phase’ occurs when the participant has their first encounter with the study personnel, most often a nurse. It is during this time that the participant is informed about the intent of the study and has a discussion about the risks and benefits (if any) of the study prior to signing the informed-consent document. It is also during this time that trust is established between the participant and the study nurse. The orientation phase occurs most often during a face-to-face experience and, as described by Peplau, it is during this time that “knowing the individual needs of the person, the nurse helps to establish caring interactions that are necessary for the relationship” [1]. Trust is essential for the participant to proceed into the ‘working phase’ of the relationship. This can be the time during which the participant engages in the activity of the study (e.g., the treatment or control) and where he/she “may learn about their current health condition, understand their condition and identify what is required for them to care for themselves” [1]. During this phase, it is important that communication continues between the participant and nurse to maintain their relationship. It is possible that as respondent burden increases (frequent data collection points); more contact is needed by the nurse to address participant concerns and/or maintain their engagement in the protocol. These interactions are often face-to-face, but may also be conducted by telephone, particularly for longitudinal studies. It is during this phase that the nurse may be challenged as she experiences conflict in her role as a ‘study nurse’ rather than as a nurse who is ‘providing care’. This conflict may or may not influence the trusting relationship that has been established (e.g., not able to disclose information due to study protocol). However, if the role performed by the nurse is not congruent with the study protocol, it can impact on the integrity of the study itself [3].

Internet Recruitment and Retention for a 6 Months’ Longitudinal Study

To examine factors influencing recruitment and retention of study participants in a longitudinal study. After completion of a longitudinal (6 months) study of long-term indwelling urinary catheter users, three types of data were analyzed: number of problems with data entry into an online survey, number of reminders sent by study staff to participants, and number and nature of e-mail contacts between participants and study staff and among study staff regarding the study. The Internet can be used effectively for research, especially involving small, specialized populations. In order to retain study subjects and obtain complete and accurate data, study staff must be closely involved and responsive to participants' issues, and technical support staff must be readily available and invested in the research project. Using the Internet to reach small, special, marginalized, or geographically dispersed populations for research is becoming common. Researchers need to know how best to recruit, support, and retain participants in Internet-based studies.

O2-2.1 Maximising the return from cohort studies

<h3>Introduction</h3> Cohort studies are important for understanding the aetiology underlying differences in disease incidence. Selective attrition is problematic as those at greater risk of ill-health are more likely to drop out, resulting in homogenous study populations with limited generalisability. Selective attrition may also bias estimates of association. For the benefits of cohort studies to be realised efforts must be made to minimise attrition and statistical methods for the analysis of studies with missing data must be developed to minimise bias. <h3>Methods</h3> We describe work examining methods used to maintain participation in cohort studies, identify best practice for reducing attrition and investigate methodologies suitable for the analysis of cohort studies with attrition under different circumstances. <h3>Results</h3> A literature search identified factors associated with minimising attrition including study design, recruitment procedures, incentives and retention methods utilised. A questionnaire including such factors was sent to 32 UK-based cohort studies; 25 (78%) returned a questionnaire. Analysis suggested that no one method is most effective, rather it is the combination of methods and study setting which may dictate the overall retention of study participants. Work with various cohort studies resulted in consideration of the appropriateness of methods for missing data. This has led to a review of inverse probability weighting (IPW) focusing on how and when to use it appropriately. The motivation for combining IPW and multiple imputation, and the theoretical justification for doing so, has been examined. A final development concerns the use of IPW when predictors of missingness are themselves missing.

Outcome Assessment in Traumatic Brain Injury Clinical Trials and Prognostic Studies

Large numbers of investigations have sought to evaluate prediction of outcome after traumatic brain injury (TBI) and the effectiveness of interventions designed to address post-TBI deficits. Unfortunately, failure to attend to key issues in experimental design regarding outcome assessment has limited the utility of these investigations. Increased attention to 5 issues in outcome assessment will increase the evidence base for TBI prognosis and treatment and increase the relevance of findings to end users of research such as other investigators, rehabilitation providers, policy makers, persons with TBI, and family members of persons with TBI. These 5 issues are (1) masking of outcome examiners, (2) retention of study participants, (3) use of surrogate informants to capture data from a wider range of study participants, (4) relevance of study outcomes to stakeholders, and (5) cultural considerations in outcome assessment.