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  • 1.  Analysing multiple before/after variables in SPSS - ANOVA?

    Posted Wed June 08, 2022 09:17 AM
    I'm using a large dataset with 12 pairs of variables that I'm interested in: a value of a particular factor before and after an intervention/control. So there's 'BeforeA', 'AfterA', 'BeforeB', 'AfterB' and so on.
    I need to analyse these and show them in a before/after line graph with all the lines together. I've spent over a week trying to learn how to do an ANOVA or ANCOVA analysis (possibly one-way between subjects ANOVA?), I've watched and copied several videos but it's always returned error results and I have no idea if I'm using the right approach.
    What method would you suggest in SPSS and can you direct me to a video demonstrating how to do it?
    Thank you so much, this is exhausting me.



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    Chris Dyke
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    #SPSSStatistics


  • 2.  RE: Analysing multiple before/after variables in SPSS - ANOVA?

    Posted Wed June 08, 2022 10:14 AM
    Hi. I made up an example that you should be able to generalize from. Run it and see if that is the kind of plot you are envisioning (of course, yours would have more lines):

    data list free /beforeA afterA beforeB afterB beforeC afterC.
begin data.
12 09 05 07 14 10
18 12 09 10 16 11
10 06 10 13 20 10
13 10 08 09 18 09
17 13 12 15 17 12
end data.

GLM beforeA beforeB beforeC afterA afterB afterC
  /WSFACTOR=time 2 Polynomial ABC 3 Polynomial 
  /METHOD=SSTYPE(3)
  /PLOT=PROFILE(time*ABC) TYPE=LINE ERRORBAR=NO MEANREFERENCE=NO YAXIS=AUTO
  /CRITERIA=ALPHA(.05)
  /WSDESIGN=time ABC time*ABC.
​

    You have two times (before, after), so time=2. Your variables would be in two 12-var groups "all 12 before", "all 12 after", something like BEFORE_01 to BEFORE_12 AFTER_01 to AFTER_12.

    Where I have the generic "ABC" you would have some sensible name that identifies what you're measuring.



    ------------------------------
    Rick Marcantonio
    Quality Assurance
    IBM
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    Original Message


  • 3.  RE: Analysing multiple before/after variables in SPSS - ANOVA?

    Posted Thu June 09, 2022 08:07 AM
    Thank you very much for your help. It was reassuring that your code was identical to mine, so I wasn't doing anything too badly wrong! It turns out it's to do with missing data - given that every subject has a different combination of variables relevant to them, there are large gaps in the data which makes a repeated measures ANOVA impossible. I'm reorganising the data into just a few columns, deleting all the empty data and then trying a one-way ANOVA instead. Thank you!

    ------------------------------
    Chris Dyke
    ------------------------------

    Original Message