Repeated attempts using different strategies are important for timely contact with study participants

Treweek, 2010, Strategies to improve recruitment to randomised controlled trials, Cochrane Database Syst Rev, 10.1002/14651858.MR000013.pub5 Easterbrook, 1992, Fate of research studies, J R Soc Med, 85, 71, 10.1177/014107689208500206 Forthofer, 1983, Investigation of nonresponse bias in NHANES II, Am J Epidemiol, 117, 507, 10.1093/oxfordjournals.aje.a113568 Jacobsen, 2004, Participation bias in a population-based echocardiography study, Ann Epidemiol, 14, 579, 10.1016/j.annepidem.2003.11.001 Tennant, 1991, Investigating non-response bias in a survey of disablement in the community: implications for survey methodology, J Epidemiol Community Health, 45, 247, 10.1136/jech.45.3.247 Kiezebrink, 2009, Strategies for achieving a high response rate in a home interview survey, BMC Med Res Methodol, 9, 46, 10.1186/1471-2288-9-46 Nystuen, 2004, Telephone reminders are effective in recruiting nonresponding patients to randomized controlled trials, J Clin Epidemiol, 57, 773, 10.1016/j.jclinepi.2003.12.015 Kiernan, 2000, Using direct mail to recruit Hispanic adults into a dietary intervention: an experimental study, Ann Behav Med, 22, 89, 10.1007/BF02895172 Boshuizen, 2006, Non-response in a survey of cardiovascular risk factors in the Dutch population: determinants and resulting biases, Public Health, 120, 297, 10.1016/j.puhe.2005.09.008 Eagan, 2002, Nonresponse in a community cohort study: predictors and consequences for exposure-disease associations, J Clin Epidemiol, 55, 775, 10.1016/S0895-4356(02)00431-6 Janzon, 1986, Factors influencing participation in health surveys. Results from prospective population study ‘Men born in 1914’ in Malmö, Sweden, J Epidemiol Community Health, 40, 174, 10.1136/jech.40.2.174 Paul, 2005, A comparison of participants and non-participants in the Chennai Glaucoma Study-rural population, Ophthalmic Epidemiol, 12, 125, 10.1080/09286580590932798 Pietila, 1995, Background factors predicting non-response in a health survey of northern Finnish young men, Scand J Soc Med, 23, 129, 10.1177/140349489502300208 Pirzada, 2004, Response rates to a questionnaire 26 years after baseline examination with minimal interim participant contact and baseline differences between respondents and nonrespondents, Am J Epidemiol, 159, 94, 10.1093/aje/kwh012 Ramos, 2004, Investigating the effect of nonparticipation using a population-based case-control study on myocardial infarction, Ann Epidemiol, 14, 437, 10.1016/j.annepidem.2003.09.013 Van Loon, 2003, Survey non-response in the Netherlands: effects on prevalence estimates and associations, Ann Epidemiol, 13, 105, 10.1016/S1047-2797(02)00257-0 Hoeymans, 1998, Non-response bias in a study of cardiovascular diseases, functional status and self-rated health among elderly men, Age Ageing, 27, 35, 10.1093/ageing/27.1.35 Haapea, 2008, Non-participation in a field survey with respect to psychiatric disorders, Scand J Public Health, 36, 728, 10.1177/1403494808092250 Rosengren, 1987, Non-participants in a general population study of men, with special reference to social and alcoholic problems, Acta Med Scand, 221, 243, 10.1111/j.0954-6820.1987.tb00890.x Needham, 2006, Study protocol: The Improving Care of Acute Lung Injury Patients (ICAP) study, Crit Care, 10, R9, 10.1186/cc3948 Cheung, 2006, Two-year outcomes, health care use, and costs of survivors of acute respiratory distress syndrome, Am J Respir Crit Care Med, 174, 538, 10.1164/rccm.200505-693OC Charlson, 1987, A new method of classifying prognostic comorbidity in longitudinal studies: development and validation, J Chronic Dis, 40, 373, 10.1016/0021-9681(87)90171-8 Funkhouser, 2000, Alternative strategies for selecting population controls: comparison of random digit dialing and targeted telephone calls, Ann Epidemiol, 10, 59, 10.1016/S1047-2797(99)00046-0 Herridge, 2003, One-year outcomes in survivors of the acute respiratory distress syndrome, N Engl J Med, 348, 683, 10.1056/NEJMoa022450 Splansky, 2007, The Third Generation Cohort of the National Heart, Lung, and Blood Institute’s Framingham Heart Study: design, recruitment, and initial examination, Am J Epidemiol, 165, 1328, 10.1093/aje/kwm021 Christen, 2000, Design of Physicians’ Health Study II—a randomized trial of beta-carotene, vitamins E and C, and multivitamins, in prevention of cancer, cardiovascular disease, and eye disease, and review of results of completed trials, Ann Epidemiol, 10, 125, 10.1016/S1047-2797(99)00042-3