title: Respondent driven sampling of wheelchair users: A lack of traction?
abstract: BACKGROUND
  Internationally, wheelchair users are an emerging demographic phenomenon, due to their increased prevalence and rapidly increasing life-span. While having significant healthcare implications, basic robust epidemiological information about wheelchair users is often lacking due, in part, to this population's 'hidden' nature. Increasingly popular in epidemiological research, Respondent Driven Sampling (RDS) provides a mechanism for generating unbiased population-based estimates for hard-to-reach populations, overcoming biases inherent within other sampling methods. This paper reports the first published study to employ RDS amongst wheelchair users.
  
  
  METHODS
  Between October 2015 and January 2016, a short, successfully piloted, internet-based national survey was initiated. Twenty seeds from diverse organisations were invited to complete the survey then circulate it to peers within their networks following a well-defined protocol. A predetermined reminder protocol was triggered when seeds or their peers failed to respond. All participants were entered into a draw for an iPad.
  
  
  RESULTS
  Overall, 19 people participated (nine women); 12 initial seeds, followed by seven second-wave participants arising from four seeds . Completion time for the survey ranged between 7 and 36 minutes. Despite repeated reminders, no further people were recruited.
  
  
  CONCLUSIONS
  While New Zealand wheelchair user numbers are unknown, an estimated 14% of people have physical impairments that limited mobility. The 19 respondents generated from adopting the RDS methodology here thus represents a negligible fraction of wheelchair users in New Zealand, and an insufficient number to ensure equilibrium required for unbiased analyses. While successful in other hard-to-reach populations, applying RDS methodology to wheelchair users requires further consideration. Formative research exploring areas of network characteristics, acceptability of RDS, appropriate incentive options, and seed selection amongst wheelchair users is needed.
authors.affiliation: School of Health Sciences, University of Canterbury, Canterbury, 8140, New Zealand; Burwood Academy of Independent Living, Christchurch, 8140, New Zealand.
authors.forename: John A
authors.initials: JA
authors.lastname: Bourke
authors.affiliation: School of Health Sciences, University of Canterbury, Canterbury, 8140, New Zealand; School of Nursing, Midwifery and Social Work, The University of Queensland, Brisbane, 4072, Australia.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Schluter
authors.affiliation: Rehabilitation Teaching and Research Unit, University of Otago Wellington, Wellington, 6242, New Zealand.
authors.forename: E Jean C
authors.initials: EJ
authors.lastname: Hay-Smith
authors.affiliation: Burwood Academy of Independent Living, Christchurch, 8140, New Zealand; Department of Orthopaedic Surgery and Musculoskeletal Medicine, University of Otago Christchurch, Christchurch, 8140, New Zealand.
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Snell
keywords: Disability; Respondent driven sampling; Sampling approaches; Social epidemiology; Wheelchair users