Date:         Wed, 25 Jul 2007 11:13:35 -0300
Reply-To:     Hector Maletta <hmaletta@fibertel.com.ar>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Hector Maletta <hmaletta@fibertel.com.ar>
Subject:      Re: stepwise regression how to include all cases despite missing
              data
Comments: To: Hunna Watson <H.Watson@curtin.edu.au>
In-Reply-To:  <025B627619018245B4278307238F0839089DE8BC@exmsp2.perth.ad.curtin.edu.au>
Content-Type: text/plain; charset="us-ascii"

         Hunna,
         Your use of the stepwise method for regression instead of running
with all the variables at once is immaterial for your problem. What you need
is some way of dealing with projects where some organizational practice does
not apply.
         You do not give many details about the variables, but I imagine
that each organizational practice might be a dummy variable, either present
or absent. In such case, you may posit its effect on costs not as a result
of "choosing or not choosing it when it is adequate to choose it" but as a
result of its mere presence. A project may benefit from a practice if (a)
the practice is applicable and (b) it is actually used; otherwise the
project does not benefit from that practice. The absence of a practice may
thus be a result of deliberate choice or impossibility of application, but
in either case it would result in its effect not being observed. In other
words, you may (if your particular situation affords this interpretation)
treat the "missing" cases as negative instances, as zeroes in the dummies,
and proceed with the regression.
         If this road is not conceptually adequate, you're in trouble.
         Hector


         -----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Hunna Watson
Sent: 25 July 2007 10:59
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: stepwise regression how to include all cases despite missing data

         Hi all,

         I'm running a stepwise regression of organizational practices on
construction projects that predict project cost growth. I have data for 115
projects, yet some organizational practices were not applicable on some
projects (in a random fashion). the missing data is obviously purposeful and
not due to not filling in questionnaires etc. spss automatically excludes
cases with any missing values, or wants to substitute a value, so I end up
with a regression being carried out on 10 projects, obviously not useful.
Any suggestions for syntax to include all cases or suggestions to rectify
this problem?

         Thanks in advance,
         Hunna Watson