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Date:         Mon, 17 Jul 2006 17:54:42 -0700
Reply-To:     Dennis Deck <DDeck@rmccorp.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Dennis Deck <DDeck@rmccorp.com>
Subject:      Re: SPSS changing data in fields
Comments: To: Janice Chang <jchang@flmnh.ufl.edu>
Content-Type: text/plain; charset="us-ascii"

I think it highly unlikely that SPSS is changing any data, though your program might be doing something other than what you intended.

The system variable $casenum should not be used as a case identifier - its value changes when you manipulate the data - it is not intended for this purpose. You should always assign a case identifier when entering your data. However, if you did not you can create one with syntax as follows: COMPUTE ID = $Casenum . The new ID variable will uniquely identify each record, it will be preserved with any modifications, and it can be used to restore the original sort order of the data.

As a rule, you should *never* make modifications of your raw data directly. Always use syntax to read and manipulate the raw data. You can save the modifications (.SAV format) or reconstruct it from the raw data whenever you need it. (Even with files far larger than yours [thousands or millions of records], it is often fast to build it when you need it and this avoids proliferation of multiple versions.) Either way you can always recreate an updated analysis file if you a) correct a coding mistake, b) learn more about the data, or c) add new data.

For good tips on file handling I suggest looking at Levesque's SPSS Programming and Data Management which is included as a PDF on the distribution disk.

Dennis Deck, PhD RMC Research Corporation ddeck@rmccorp.com

-----Original Message----- From: Janice Chang [mailto:jchang@flmnh.ufl.edu] Sent: Friday, July 14, 2006 9:04 AM Subject: SPSS changing data in fields

I've been working with large data files consisting of over 500 individual cases. For the past several weeks, SPSS has been replacing some cases with others. For example, rather than having cases 1, 2, 3, 4, 5, 6, 7, 8...., I'll end up with 1, 2, 3, 4, 5, 2, 3, 8... The first variable is the case number. Sorting by the case number lists the cases as 1, 2, 2, 3, 3, 4, 5, 8 which tells me that my data is being deleted and replaced rather than being rearranged. I have tried re-entering those cases and inserting new case fields in the event that those fields have been corrupted in some way. Eventually, it always reverts back. Any ideas on what SPSS is doing or what I'm doing wrong?

Thanks in advance. ~janice

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~~~~~~~~~~~~~~~~~~~~~~~~~~~ Janice Chang MESS Research Associate

Center for Informal Science Education Florida Museum of Natural History Powell Hall University of Florida P.O. Box 112710 Gainesville, FL 32611-2710

Phone: (352) 846-2000 x 268 Fax: (352) 846-0253


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