Hypotheses: when considering a definition for non-responders, one may
need to be prudent over the precise wording, because there are
different categories of volunteers and non-responders, e.g. for the
latter slow - or very slow - responders (speed definition here may
provide another complexity), post-deadline (if any) non-responders,
etc.. If such (and indeed any other) non-responders populations were
present, considerable heterogeneity in non-responders populations may
result, thereby influencing Materials & Methods heterogeneities,
validity in study comparisons, validity in meta-analyses, etc..
Likewise potentially for the definition of volunteers, e.g. active,
passive, motivated, unwilling, informed, expressed, etc., and any
categories for the latter, e.g. very, somewhat, moderately, etc..
On 27 June 2011 16:30, Stephen Senn <[log in to unmask]> wrote:
> Your assessment seems makes sense to me. I would say that the one describes the individuals you see and the other those you don't but they are, as you say, two sides of the same coin.
> Stephen
>
>
> Stephen Senn
>
> Professor of Statistics
> School of Mathematics and Statistics
> Direct line: +44 (0)141 330 5141
> Fax: +44 (0)141 330 4814
> Private Webpage: http://www.senns.demon.co.uk/home.html
>
> University of Glasgow
> 15 University Gardens
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>
> The University of Glasgow, charity number SC004401
> ________________________________________
> From: A UK-based worldwide e-mail broadcast system mailing list [[log in to unmask]] On Behalf Of Dr Philip Sedgwick [[log in to unmask]]
> Sent: 27 June 2011 15:29
> To: [log in to unmask]
> Subject: Volunteer bias / non-response bias
>
> Dear fellow Allstaters
>
> Was wondering if anyone has an opinion on the definitions of volunteer
> bias and non-response bias, especially in context of questionnaire
> surveys. There is some potential overlap but I do not believe that one
> is a simple inverse of the other.
> Any thoughts
> Best wishes
> Philip Sedgwick
>
> __________________________________________
> Dr. Philip Sedgwick
> Senior Lecturer in Medical Statistics,
> Academic Lead and Chief Examiner for SSCs and Projects
> Section of Medical and Healthcare Education,
> Room 6.30, Sixth Floor, Hunter Wing
> St. George's, University of London,
> London SW17 0RE
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