Date: Thu, 10 Jul 2003 17:03:40 +0100
Reply-To: David Hitchin <D.H.Hitchin@sussex.ac.uk>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: David Hitchin <D.H.Hitchin@sussex.ac.uk>
Subject: Re: Problem selecting first cases
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You need to create a variable which is true if the case number is different
from the previous one, I'll call it "first".
I am assuming that you have or can create a variable which I have called
case, so that you know when the next child's record starts. Then some
possible code looks like this
DO IF $casenum=1.
COMPUTE first= (time ~=lag(time)) OR (case ~=lag(case)).
Note that we have to deal with the first case separately, since there isn't
a previous case to compare it with to see if it has changed.
--On 10 July 2003 09:35 -0600 Susan Crawford
> Hi, everyone.
> We have just finished a huge study of reaction time in children, and
> have run into trouble selecting cases for analysis.
> The problem is that after the positive target was displayed, in some
> trials, the child made the correct response once and in other trials,
> the child made the response three or four times. We only want to look
> at the first response if the child made more than one for that trial
> when we do our analysis.
> The data file looks like this:
> Type of Target Time Target Came On Time Key Was Hit
> Positive 1 45
> Positive 1 75
> Positive 1 95
> Negative 100
> Positive 300 405
> So for the data file above, I would only want to have the first record,
> fourth and fifth. The file for each child ends up being over 1000
> records long, so I need to be able to use syntax to do this.
> Many thanks for helping us!!
> Susan Crawford, M.Sc.
> Research Coordinator
> Behavioural Research Unit
> Alberta Children's Hospital
> Phone: (403) 943-7364
> FAX: (403) 543-9100