Date: Wed, 25 Aug 1999 03:49:19 +0100
Reply-To: John Whittington <medisci@POWERNET.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: John Whittington <medisci@POWERNET.COM>
Subject: Re: Missing Values (... not so fast!)
In-Reply-To: <199908241843.TAA13319@mail-relay.power.net.uk>
Content-Type: text/plain; charset="us-ascii"
At 14:47 24/08/99 -0400, Peter Flom wrote:
>With regard to missing data on surveys, we also need to
>distinguish "missing because of deliberate skip", e.g.
>we don't ask people with no kids how old their kids are.
Yes, of course - and this is obviously one of those situations in which
coding missing ('missing because not applicable') as numerical zero would
have disastrous effects on summary data.
>But even this can get complicated. In our research, we ask a lot of
sensitive
>questions about things like use of illicit drugs. We ask about these in
>several ways. So, a person who says to the question "Have you ever used
>cocaine?" on one section will then not be asked "How old were you when
>you first used cocaine?"
Yes, as I need not tell you, there are many approaches that can be taken to
those sort of questions. Some people believe that one sometimes gets most
honest answers by not asking the 'filter' question ('have you ever used
...?) at all. In my previous life as a physician, I was certainly taught
to take this approach when trying to get fairly honest information about
consumption of alcohol, tobacco, illicit drugs, food or whatever, or
questions about sexual activity etc. - the idea being to almost give the
impression that one is expecting a 'positive' answer, so as to reduce
hesitance or embarrassment. Hence, one might ask how much someone smokes,
without first asking them *whether* they smoke - or ask a patient how many
extra-marital sexual partners they have had, rather than 'whether'.
However, this has precious little to do with SAS!
Regards,
John
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