Dear David,
How would you adjust the confidence interval to account for non-respondents?
Can you indicate how you would do that in SPSS or STATA?
Thanks
Samer Jabbour, MD, MPH
> There is one message totalling 51 lines in this issue.
>
> Topics of the day:
>
> 1. appraise questionnaire surveys (fwd)
>
> ----------------------------------------------------------------------
>
> Date: Fri, 27 Apr 2001 08:01:42 -0700
> From: David Birnbaum <[log in to unmask]>
> Subject: Re: appraise questionnaire surveys (fwd)
>
> Roy Poses posted:
> > All this is very reasonable if you are doing a survey to find out about
> > prevalence, e.g., a survey sent to patients about their recent dietary
> intake.
> > And I suppose this is the most common reason one does surveys.
> >
> > But I would like to mention a somewhat special case. Sometimes we do true
> > psychological experiments in a paper and pencil format that resemble
> surveys.
> > So, for example, I might send out patient vignettes to physicians that
> vary
> > according to specific characteristics, with the goal of seeing whether the
> > physicians' responses vary according to these characteristics. In this
> case,
> > the response rate affects the generalizability of the study, but not the
> > internal validity. Thus, the minimum acceptable response rate in such a
> > circumstance is not so clear. Whether a less than 60% response rate
> > invalidates such a study is very arguable. (Although I have gotten papers
> > that reported such work rejected because the response rate was 60%.) Note
> > that in other forms of experiments, RCT's, we often accept response rates
> > (in terms of the proportions of patients offered enrollment who actually
> > enroll) of much less than 60%.
>
> Regardless of purpose (which may range from estimating prevalence to market
> research to exploring individual preferences, etc.), the point remains that
> relatively few surveys seem to adjust the width of confidence intervals
> reported to compensate for non-response. If comparison of the nature of
> respondents to the nature of subjects in the sampling frame shows reasonable
> match on demographic factors, and evaluation of successive waves of response
> shows no problematic trends, and expanded confidence interval limits still
> permit a decision, then one might still gain insight from a survey with low
> response rate. However, relatively few surveys seem to adjust confidence
> interval width (as Cochran's book advises) to reflect potential impact of
> nonresponse rate observed, an adjustment that could be done in any survey
> whether "special case" or not.
>
> David.
> David Birnbaum, PhD, MPH
> Clinical Assistant Professor
> Dept. of Health Care & Epidemiology
> University of British Columbia, Canada
>
> ------------------------------
>
> End of EVIDENCE-BASED-HEALTH Digest - 27 Apr 2001 to 28 Apr 2001 (#2001-9)
> **************************************************************************
>
Samer Jabbour, MD, MPH
Faculty of Health Sciences
American University of Beirut
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