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Date:         Thu, 31 Oct 2002 12:38:40 +0000
Reply-To:     "R. Allan Reese" <R.A.Reese@gri.hull.ac.uk>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "R. Allan Reese" <R.A.Reese@gri.hull.ac.uk>
Subject:      Mult Response - "Misleading cases"
Content-Type: TEXT/PLAIN; charset=US-ASCII

The subject line is based on the title of a book by AP Herbert, and the message is to draw attention to a feature of Mult Response that is documented and logical, but so potentially dangerous as to be flagged as needing attention. It's a feature rather than a bug, but a feature that is as helpful as Macbeth's witches.

The problem emerged when I showed a client how to use MR with multiple dichotomies and compared the marginal figures with totals she had tabulated for individual variables. MR showed lower counts and a lower overall total. MR reported missing cases, though there were none in her data. We tried "/MISSING=INCLUDE" but nothing changed. MR frequencies showed the counts she already had; MR crosstabs had different margins.

Cutting straight to the answer, "For a multiple-response group, a case is considered missing if none of the components has valid values falling within the tabulated range for that case." The keywords in subcommands affect the treatment of missing values in the component variables. Logical, but not what the client wanted or expected. In the CROSSTABS command, "/MISSING=INCLUDE" creates additional rows or columns, so there ought to be an equivalent in MR.

Here's a work-round example:

* Define additional category for "no response selected". count norow = rowvar1 to rowvarN (1). recode norow (0=1)(else=0). count nocol = colvar1 to colvarM (1). recode nocol (0=1)(else=0). mult response groups = $row (rowvar1 to rowvarN norow (1)) $col (colvar1 to colvarM nocol (1)) / tables = $row by $col.

Request to SPSS: It is probably a bad idea to redefine the action of existing syntax, but treating non-responses as MISSING is inconsistent with the rest of SPSS. The output might be adapted to read, instead of "missing cases", "cases excluded because of no responses in set <name> = <number>", which would be repeated for each group variable in the table. The action achieved above could be provided through a new option in the groups subcommand, eg, /groups = $row (rowvar1 to rowvarN (1)(noresponse)).

R. Allan Reese Email: r.a.reese@gri.hull.ac.uk Associate Manager GRI Direct voice: +44 1482 466845 Graduate School Voice messages: +44 1482 466844 Hull University, Hull HU6 7RX, UK. Fax: +44 1482 466436 ====================================================================


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