Differential Attrition Research Articles

The Longer, the Better? An Empirical Study of the Extent and Mechanisms of Attenuating Biomarker Associations in Cardiovascular Patient Cohorts.

Identifying novel risk markers in cardiovascular patients remains a research priority. Longer follow-up generally is considered favorable in such studies, but associations of interest may become attenuated with increasing follow-up. This issue has not been adequately addressed in the context of patient cohorts. The current study analyzed the extent and mechanisms of attenuating associations in a cardiovascular patient cohort. The associations of numerous biomarkers with all-cause mortality were estimated by multiple Cox regression in the Langzeiterfolge der KARdiOLogischen Anschlussheilbehandlung (KAROLA) prospective cohort study of 1204 patients who had participated in an inpatient rehabilitation program after an acute coronary syndrome (ACS) or coronary bypass operation. Hazard ratios were estimated based on the entire follow-up period (13 years), and after truncation at previous follow-up times (3, 4.5, 6, 8, 10 years). For the majority of markers, a clear and sometimes very pronounced attenuation of the hazard ratios could be observed with increasing follow-up duration. Differential attrition generally was not a sufficient explanation for this phenomenon, whereas further analyses suggested a role for reverse causality for some of the markers. Power analyses showed that the relationship of follow-up duration and statistical power can be counterintuitive in the presence of realistic amounts of attenuation. The attenuation of estimates of association in patient cohorts is a much more substantial and complex issue than currently appreciated. This has important implications for the design and interpretation of prognostic, as well as etiologic, studies which may be particularly relevant in the case of patient cohorts defined by an initial acute event.

Accelerated telomere shortening: Tracking the lasting impact of early institutional care at the cellular level.

Studies examining the association between early adversity and longitudinal changes in telomere length within the same individual are rare, yet are likely to provide novel insight into the subsequent lasting effects of negative early experiences. We sought to examine the association between institutional care history and telomere shortening longitudinally across middle childhood and into adolescence. Buccal DNA was collected 2-4 times, between the ages of 6 and 15 years, in 79 children enrolled in the Bucharest Early Intervention Project (BEIP), a longitudinal study exploring the impact of early institutional rearing on child health and development. Children with a history of early institutional care (n=50) demonstrated significantly greater telomere shortening across middle childhood and adolescence compared to never institutionalized children (n=29). Among children with a history of institutional care, randomization to high quality foster care was not associated with differential telomere attrition across development. Cross-sectional analysis of children randomized to the care as usual group indicated shorter telomere length was associated with greater percent of the child's life spent in institutional care up to age 8. These results suggest that early adverse care from severe psychosocial deprivation may be embedded at the molecular genetic level through accelerated telomere shortening.

Patterns and Predictors of Compliance in a Prospective Diary Study of Substance Use and Sexual Behavior in a Sample of Young Men Who Have Sex With Men.

Behavioral diaries are used for observing health-related behaviors prospectively. Little is known about patterns and predictors of diary compliance to better understand differential attrition. An analytic sample of 241 young men who have sex with men (YMSM) from a 2-month diary study of substance use and sexual behavior were randomized to complete daily or weekly timeline followback diaries. Latent class growth analyses were used to analyze data. Weekly and daily diary groups produced similar compliance patterns: high, low, and declining compliance groups. Black YMSM were more likely to be in the declining compared with the high compliance group. YMSM who were randomly assigned to receive automated feedback about risk behaviors did not differ in compliance rate compared with those who did not. Risk behavior engagement did not predict compliance in the daily condition, but some substances predicted compliance in the weekly condition. Implications for observational and behavior change methods are discussed.

Differential Teacher Attrition: Do High-Ability Teachers Exit at Higher Rates?

Prior evidence of differential teacher attrition is conflicting. Studies that use proxies such as certification scores, SAT or ACT scores, or the selectivity of the teacher’s undergraduate institution tend to find that attrition is highest among high-ability teachers. In contrast, many studies that use value-added measures find that teachers with high value-added scores have lower attrition rates. This work presents new evidence on the nature of differential teacher attrition in Texas and attempts to reconcile these conflicting results. Using teacher certification scores as a proxy for teacher ability, this work finds that differential attrition varies with teacher experience. Among new teachers, attrition is concentrated among the least able, but after the first year, attrition rates are highest among high-ability teachers. These findings could explain why many studies that focus on early-career attrition tend to find that low-ability teachers have higher attrition rates. Other conflicting results may be explained by how studies measure teacher ability. Many value-added studies may confound teacher ability with experience, effort, and unobserved school attributes making it appear, perhaps incorrectly, as though the most able teachers have lower attrition rates. Prior studies that carefully measure teacher ability over longer career trajectories tend to corroborate the alarming conclusion that public schools are losing their most able teachers.

Can Targeted Intervention Mitigate Early Emotional and Behavioral Problems?: Generating Robust Evidence within Randomized Controlled Trials.

This study examined the impact of a targeted Irish early intervention program on children’s emotional and behavioral development using multiple methods to test the robustness of the results. Data on 164 Preparing for Life participants who were randomly assigned into an intervention group, involving home visits from pregnancy onwards, or a control group, was used to test the impact of the intervention on Child Behavior Checklist scores at 24-months. Using inverse probability weighting to account for differential attrition, permutation testing to address small sample size, and quantile regression to characterize the distributional impact of the intervention, we found that the few treatment effects were largely concentrated among boys most at risk of developing emotional and behavioral problems. The average treatment effect identified a 13% reduction in the likelihood of falling into the borderline clinical threshold for Total Problems. The interaction and subgroup analysis found that this main effect was driven by boys. The distributional analysis identified a 10-point reduction in the Externalizing Problems score for boys at the 90th percentile. No effects were observed for girls or for the continuous measures of Total, Internalizing, and Externalizing problems. These findings suggest that the impact of this prenatally commencing home visiting program may be limited to boys experiencing the most difficulties. Further adoption of the statistical methods applied here may help to improve the internal validity of randomized controlled trials and contribute to the field of evaluation science more generally.Trial Registration: ISRCTN Registry ISRCTN04631728

Investigating the feasibility, acceptability and appropriateness of outreach case management in an urban Aboriginal and Torres Strait Islander primary health care service: a mixed methods exploratory study.

BackgroundThe disparities in health and life expectancy of Aboriginal and Torres Strait Islander peoples compared to non-Indigenous Australians are well documented. Chronic diseases are a leading contributor to these disparities. We aimed to determine the feasibility, acceptability and appropriateness of a case management approach to chronic disease care integrated within an urban Aboriginal and Torres Strait Islander primary health care service.MethodsThe Home-based, Outreach case Management of chronic disease Exploratory (HOME) Study provided holistic, patient centred multidisciplinary care for Aboriginal and Torres Strait Islander people with chronic disease. A developmental evaluation approach supported the implementation and ongoing adaptations in the delivery of the model of care, and ensured its alignment with Aboriginal and Torres Strait Islander peoples’ understandings of, and approaches to, health and wellbeing. In-depth, semi-structured interviews were conducted with nine patient participants (one interview also included a participant’s spouse) and 15 health service staff and key themes were identified through an iterative reflective process. Quantitative data were collected directly from patient participants and from their medical records at baseline, 3 and 6 months. Patient participants’ baseline characteristics were described using frequencies and percentages. Attrition and patterns of missing values over time were evaluated using binomial generalized estimating equation (GEE) models and mean differences in key clinical outcomes were determined using normal GEE models.ResultsForty-one patients were recruited and nine withdrew over the 6 month period. There was no evidence of differential attrition. All participants (patients and health service staff) were very positive about the model of care. Patient participants became more involved in their health care, depression rates significantly decreased (p = 0.03), and significant improvements in systolic blood pressure (p < 0.001) and diabetes control (p = 0.05) were achieved.ConclusionsThe exploratory nature of our study preclude any definitive statements about the effectiveness of our model of care. However, staff and patients' high levels of satisfaction and improvements in the health and wellbeing of patients are promising and suggest its feasibility, acceptability and appropriateness. Further research is required to determine its efficacy, effectiveness and cost-effectiveness in improving the quality of life and quality of care for Aboriginal and Torres Strait Islander peoples living with chronic disease.

Challenges in Using the Randomized Trial Design to Examine the Influence of Treatment Preferences.

The overall purpose of this methodological study was to investigate the strengths and limitations of the randomized clinical trial design in examining the influence of treatment preferences on outcomes. The study was a secondary analysis of data obtained in two randomized clinical trials that evaluated behavioral therapies for insomnia. In both trials, the same design and methods were used to assess participants' treatment preferences and outcomes, however, the treatments differed. The results illustrated the challenges encountered in using the randomized clinical trial design. The challenges were related to the unbalanced distribution of participants with preferences for the study treatments, non-comparability of the subgroups with treatments matched or mismatched to their preferences, differential attrition, which compromised the sample size and composition of the subgroups and limited the use of the planned statistical analyses. Whether these challenges occur in trials of other types of treatments and target populations should be explored in future research. Some strategies were proposed and should be evaluated for their utility in addressing these challenges.

Reported reasons for missing data and the interplay with trial setting

Missing data in clinical trials is common. It can reduce trial efficiency and bias the estimate of treatment effect. Much emphasis is placed on addressing missing data in trial design. However, strategies need to be informed by the reasons for attrition which are likely to vary according to trial context. In order to develop effective interventions to minimise missing data, it is important to not only understand the causes but also their interplay with the trial setting. We present the reported reasons for missing data within a cohort of 168 randomised trials published in four major journals in 2013 and 36 Health Technology Assessment programme monographs published 2009-2014. We discuss the frequency of missing data and differential attrition resulting from causes such as withdrawals due to treatment tolerance or efficacy, inability to measure the primary outcome due to intervening outcomes such as death or illness, laboratory or technological problems, missed measurements by clinical staff and failure of patients to attend visits or return measurements. The frequency of Investigator led post randomisation exclusions will also be reviewed, looking at data excluded for reasons such as protocol violations, post randomisation ineligibility, patients not receiving the intervention or poor treatment adherence. Levels of missing data and associations with trial setting such as clinical speciality, method and location of primary outcome measurement, nature of the intervention and control, mean age of recruited patients, number of trial centres and countries will be presented.

Early intervention and child physical health: Evidence from a Dublin-based randomized controlled trial

This article investigates the impact of an early intervention program, which experimentally modifies the parenting and home environment of disadvantaged families, on child physical health in the first 3 years of life. We recruited and randomized 233 (115 intervention, 118 control) pregnant women from a socioeconomically disadvantaged community in Dublin, Ireland into an intervention or control group. The treatment includes regular home visits commencing antenatally and an additional parenting course commencing at 2 years. Maternal reports of child health are assessed at 6, 12, 18, 24, and 36 months. Treatment effects are estimated using permutation testing to account for small sample size, inverse probability weighting to account for differential attrition, and both the stepdown procedure and an indices approach to account for multiple hypothesis testing. Following adjustment for multiple testing and attrition, we observe a positive and statistically significant main treatment effect for wheezing/asthma. The intervention group are 15.5 percentage points (pp) less likely to require medical attention for wheezing/asthma compared to the control group. Subgroup analysis reveals more statistically significant adjusted treatment effects for boys than girls regarding fewer health problems (d=0.63), accidents (23.9pp), and chest infections (22.8–37.9pp). Our results suggest that a community-based home visiting program may have favorable impacts on early health conditions.

The SOS Suicide Prevention Program: Further Evidence of Efficacy and Effectiveness.

This study replicated and extended previous evaluations of the Signs of Suicide (SOS) prevention program in a high school population using a more rigorous pre-test post-test randomized control design than used in previous SOS evaluations in high schools (Aseltine and DeMartino 2004; Aseltine et al. 2007). SOS was presented to an ethnically diverse group of ninth grade students in technical high schools in Connecticut. After controlling for the pre-test reports of suicide behaviors, exposure to the SOS program was associated with significantly fewer self-reported suicide attempts in the 3 months following the program. Ninth grade students in the intervention group were approximately 64% less likely to report a suicide attempt in the past 3 months compared with students in the control group. Similarly, exposure to the SOS program resulted in greater knowledge of depression and suicide and more favorable attitudes toward (1) intervening with friends who may be exhibiting signs of suicidal intent and (2) getting help for themselves if they were depressed or suicidal. In addition, high-risk SOS participants, defined as those with a lifetime history of suicide attempt, were significantly less likely to report planning a suicide in the 3 months following the program compared to lower-risk participants. Differential attrition is the most serious limitation of the study; participants in the intervention group who reported a suicide attempt in the previous 3 months at baseline were more likely to be missing at post-test than their counterparts in the control group.

Online Alcohol Assessment and Feedback for Hazardous and Harmful Drinkers: Findings From the AMADEUS-2 Randomized Controlled Trial of Routine Practice in Swedish Universities.

BackgroundPrevious research on the effectiveness of online alcohol interventions for college students has shown mixed results. Small benefits have been found in some studies and because online interventions are inexpensive and possible to implement on a large scale, there is a need for further study.ObjectiveThis study evaluated the effectiveness of national provision of a brief online alcohol intervention for students in Sweden.MethodsRisky drinkers at 9 colleges and universities in Sweden were invited by mail and identified using a single screening question. These students (N=1605) gave consent and were randomized into a 2-arm parallel group randomized controlled trial consisting of immediate or delayed access to a fully automated online assessment and intervention with personalized feedback.ResultsAfter 2 months, there was no strong evidence of effectiveness with no statistically significant differences in the planned analyses, although there were some indication of possible benefit in sensitivity analyses suggesting an intervention effect of a 10% reduction (95% CI –30% to 10%) in total weekly alcohol consumption. Also, differences in effect sizes between universities were seen with participants from a major university (n=365) reducing their weekly alcohol consumption by 14% (95% CI –23% to –4%). However, lower recruitment than planned and differential attrition in the intervention and control group (49% vs 68%) complicated interpretation of the outcome data.ConclusionsAny effects of current national provision are likely to be small and further research and development work is needed to enhance effectiveness.Trial RegistrationInternational Standard Randomized Controlled Trial Number (ISRCTN): 02335307; http://www.isrctn.com/ISRCTN02335307 (Archived by WebCite at http://www.webcitation.org/6ZdPUh0R4).

The healthy worker effect: Do health problems predict participation rates in, and the results of, a follow-up survey?

To determine the impact of the healthy worker effect (HWE) as a bias for the external and internal validity of the follow-up assessment in prospective survey research. Specifically, the study examined (1) whether the health status of respondents at the baseline measurement influenced response at the follow-up survey (external validity) and (2) whether HWE is a threat to internal validity by differential attrition, i.e., whether associations between work and health at baseline differ between stayers and dropouts. In a two-wave questionnaire survey with a 2-year time lag comprising 6283 persons, 4392 responded at both time points (response rate 70%). Mental distress and somatic symptoms served as indicators of health. Role conflict and role clarity were indicators of work factors. There were few differences in response rate at follow-up between persons with and without health complaints at the baseline measurement. As response rate increased incrementally with educational level, there seems to be a socio-educational bias, rather than a HWE bias on survey participation. Baseline relationships between work factors and health indicators were equal in magnitude among stayers and dropouts. The health status of participants at baseline seems to have little impact on the external and internal validity of the follow-up assessment in prospective survey research. Hence, the findings provide little support to the HWE as a potential bias in prospective studies within occupational health research. A limitation of the study is that the findings do not inform about the impact of the HWE on participation in the baseline assessment.

Field of study variation throughout the college pipeline and its effect on the earnings gap: Differences between ethnic and immigrant groups in Israel

This study demonstrates the analytical leverage gained from considering the entire college pipeline—including the application, admission and graduation stages—in examining the economic position of various groups upon labor market entry. The findings, based on data from three elite universities in Israel, reveal that the process that shapes economic inequality between different ethnic and immigrant groups is not necessarily cumulative. Field of study stratification does not expand systematically from stage to stage and the position of groups on the field of study hierarchy at each stage is not entirely explained by academic preparation. Differential selection and attrition processes, as well as ambition and aspirations, also shape the position of ethnic groups in the earnings hierarchy and generate a non-cumulative pattern. These findings suggest that a cross-sectional assessment of field of study inequality at the graduation stage can generate misleading conclusions about group-based economic inequality among workers with a bachelor’s degree.

Long-Term Consequences of Adolescent Parenthood Among African-American Urban Youth: A Propensity Score Matching Approach

PurposeThe aim of this study was to improve understanding of long-term socioeconomic consequences of teen parenting for men and women. MethodsAnalysis is based on the Woodlawn Study, a longitudinal study of an African-American cohort from a socially disadvantaged community in Chicago; data were collected at childhood (N = 1,242), adolescence (N = 705), young adulthood (age 32 years, N = 952), and midlife (age 42 years, N = 833). This analysis focused on the 1,050 individuals with data on teen parenting. We used propensity score matching to account for differences in background characteristics between teenage parents and their peers and used multiple imputation to account for differential attrition. ResultsThe regression models after propensity score matching showed that at the age of 32 years, in comparison to nonteen mothers, teenage mothers were more likely to be unemployed, live in poverty, depend on welfare, and have earned a GED or completed high school compared to finishing college. At the age of 32 years, teen fathers were more likely to be without a job than nonteen fathers. At the age of 42 years, the effect of teen parenting for women remained statistically significant for education and income. There were no significant associations between teen parenting and outcomes for men at the age of 42 years. ConclusionsSocioeconomic consequences of teenage parenting among African-Americans from disadvantaged background seem to be primarily concentrated in women and persist throughout adulthood. In addition to promoting the delay of parenting after the teenage years, it is critical to provide programs at early stages in the life course to mitigate the negative socioeconomic consequences of teenage motherhood as effects for women are broad.

Recruitment and retention strategies and the examination of attrition bias in a randomised controlled trial in children's centres serving families in disadvantaged areas of England.

BackgroundFailure to retain participants in randomised controlled trials and longitudinal studies can cause significant methodological problems. We report the recruitment and retention strategies of a randomised controlled trial to promote fire-related injury prevention in families with pre-school children attending children’s centres in disadvantaged areas in England.MethodsThirty-six children’s centres were cluster randomised into one of three arms of a 12-month fire-related injury prevention trial. Two arms delivered safety interventions and there was one control arm. Retention rates compared the numbers of participants responding to the 12-month questionnaire to the number recruited to the trial. Multivariable random effects logistic regression was used to explore factors independently associated with participant retention.ResultsThe trial exceeded its required sample size through the use of multiple recruitment strategies. All children’s centres remained in the study, despite increased reorganisation. Parent retention was 68% at 12 months, ranging from 65% to 70% across trial arms and from 62% to 74% across trial sites. There was no significant difference in the rates of retention between trial arms (p = 0.58) or between trial sites (p = 0.16). Retention was significantly lower amongst mothers aged 16–25 years than older mothers [adjusted odds ratio (AOR) 0.57, 95% CI 0.41, 0.78], those living in non-owner occupied accommodation than in owner occupied accommodation (AOR 0.53, 95% CI 0.38, 0.73) and those living in more disadvantaged areas (most versus least disadvantaged quintiles AOR 0.50, 95% CI 0.30, 0.82).ConclusionsStudies recruiting disadvantaged populations should measure and report attrition by socioeconomic factors to enable determination of the extent of attrition bias and estimation of its potential impact on findings. Where differential attrition is anticipated, consideration should be given to over-sampling during recruitment and targeted and more intensive strategies of participant retention in these sub-groups. In transient populations collection of multiple sources of contact information at recruitment and throughout the study may aid retention.Trial registrationClinicaltrials.gov identifier: NCT01452191; Date of registration: 10 October 2011, ISRCTN65067450.

Weak Markets, Strong Teachers: Recession at Career Start and Teacher Effectiveness

How do alternative job opportunities affect teacher quality? We provide the first causal evidence on this question by exploiting business cycle conditions at career start as a source of exogenous variation in the outside options of potential teachers. Unlike prior research, we directly assess teacher quality with value-added measures of impacts on student test scores, using administrative data on 33,000 teachers in Florida public schools. Consistent with a Roy model of occupational choice, teachers entering the profession during recessions are significantly more effective in raising student test scores. Results are supported by placebo tests and not driven by differential attrition.

Differential attrition in health behaviour change trials: A systematic review and meta-analysis

Objective: Attrition is a common problem in health behaviour change (HBC) trials. When the degree of attrition differs between treatment conditions, then this is called differential attrition and is regarded as a major threat to internal validity. The primary research question of this study was: how often and to what degree does differential attrition occur in HBC trials?Design: A systematic review and meta-analysis of a random selection of HBC trials (k = 60). We meta-analysed the relative attrition rates using a random-effects model and examined the relationship between the relative attrition rates and the potential moderators: the amount of human contact in delivery and the intensity of the intervention/control condition, the type of control condition, and the follow-up intensity and duration.Main outcome measures: Relative attrition rates.Results: The average attrition rate was 18% (SD = .15; M = .15) in the intervention and 17% (SD = .13; M = .13) in the control conditions. The estimated average relative attrition rate was 1.10 (95% CI: 1.01–1.20, p = .02), suggesting an overall higher attrition rate of 10% in the intervention conditions. This relative attrition rate was not related to any of the potential moderators.Conclusion: There is indication of a slightly higher amount of attrition on average in the intervention conditions of HBC trials.

Keep on brushing: a longitudinal study of motivational text messaging in young adults aged 18-24 years receiving Work and Income Support.

Using text messaging, underpinned by the Health Belief Model, this study aimed to improve tooth brushing frequencies among unemployed young adults aged 18-24 years. Set within Work and Income's Linwood Community Link office (one Christchurch branch of the New Zealand Government's employment and beneficiary services), unemployed young adults aged 18-24 years with access to a mobile phone were recruited using either a purpose-built computer kiosk or Work and Income's Facebook site. Participants completed a baseline survey and then received and responded to a series of motivational text messages over 10 weeks. Self-reported tooth brushing frequency was the primary outcome variable. Important socio-demographic (age, gender, ethnicity, employment status) and method-specific (level of attrition, distribution of successful text messages deliveries, active withdrawal) variables were also collected. Longitudinal analyses of these responses employed generalized estimating equation (GEE) models. Four hundred and three registered for the trial, of whom 171 (42%) were eligible. Self-reported tooth brushing twice or more per day increased from 51% at baseline to 70% at week 3, 74% at week 6, and 73% at week 9 - an increase significant in crude (P<0.001) and adjusted (P<0.001) GEE analyses. No important differences were noted between age, gender, or ethnic groups, although attrition was relatively high with only 26% participating by week 9. However, no evidence of differential attrition was observed. Invention through motivational text messaging improved the measured oral health self-care behavior in a hard-to-reach group carrying a disproportionately heavy oral health burden. This intervention warrants further investigation.

The STRIDE weight loss and lifestyle intervention for individuals taking antipsychotic medications: a randomized trial.

The STRIDE study assessed whether a lifestyle intervention, tailored for individuals with serious mental illnesses, reduced weight and diabetes risk. The authors hypothesized that the STRIDE intervention would be more effective than usual care in reducing weight and improving glucose metabolism. The study design was a multisite, parallel two-arm randomized controlled trial in community settings and an integrated health plan. Participants who met inclusion criteria were ≥18 years old, were taking antipsychotic agents for ≥30 days, and had a body mass index ≥27. Exclusions were significant cognitive impairment, pregnancy/breastfeeding, recent psychiatric hospitalization, bariatric surgery, cancer, heart attack, or stroke. The intervention emphasized moderate caloric reduction, the DASH (Dietary Approaches to Stop Hypertension) diet, and physical activity. Blinded staff collected data at baseline, 6 months, and 12 months. Participants (men, N=56; women, N=144; mean age=47.2 years [SD=10.6]) were randomly assigned to usual care (N=96) or a 6-month weekly group intervention plus six monthly maintenance sessions (N=104). A total of 181 participants (90.5%) completed 6-month assessments, and 170 (85%) completed 12-month assessments, without differential attrition. Participants attended 14.5 of 24 sessions over 6 months. Intent-to-treat analyses revealed that intervention participants lost 4.4 kg more than control participants from baseline to 6 months (95% CI=-6.96 kg to -1.78 kg) and 2.6 kg more than control participants from baseline to 12 months (95% CI=-5.14 kg to -0.07 kg). At 12 months, fasting glucose levels in the control group had increased from 106.0 mg/dL to 109.5 mg/dL and decreased in the intervention group from 106.3 mg/dL to 100.4 mg/dL. No serious adverse events were study-related; medical hospitalizations were reduced in the intervention group (6.7%) compared with the control group (18.8%). Individuals taking antipsychotic medications can lose weight and improve fasting glucose levels. Increasing reach of the intervention is an important future step.

Waiting list randomized controlled trial within a case-finding design: methodological considerations.

Randomized controlled trials (RCTs) are widely used in health care research to provide high-quality evidence of effectiveness of an intervention. However, sometimes a study does not require an RCT in order to answer its primary objective; a case-finding design may be more appropriate. The aim of this paper was to introduce a new study design that nests a waiting list RCT within a case-finding study. An example of the new study design is the DOC Study, which primarily aims to determine the diagnostic accuracy of lung function tests for chronic obstructive pulmonary disease. It also investigates the impact of lung function tests on smoking behaviour through use of a waiting list design. The first step of the study design is to obtain participants' consent. Individuals are then randomized to one of two groups; either the 'intervention now' group or the 'intervention later' group, that is, participants are placed on a waiting list. All participants receive the same intervention; the only difference between the groups is the timing of the intervention. The design addresses patient preference issues and recruitment issues that can arise in other trial designs. Potential limitations include differential attrition between study groups and potential demoralization for the 'intervention later' group. The 'waiting list case-finding trial' design is a valuable method that could be applied to case-finding studies; the design enables the case-finding component of a study to be maintained while simultaneously exploring additional hypotheses through conducting a trial.