Post-hoc comparisons for Friedman test
As a non-parametric test of mean differences for dependent samples SPSS implements the Friedman test. However, SPSS does not provide post-hoc tests to decide which groups are significantly different from each other. Schaich and Hamerle (1984) as well as Conover (1971, 1980) propose such post-hoc tests that are based upon the mean rank differences of the groups. These procedures are detailed in Bortz, Lienert and Boehnke (2000, pp. 275).
Note: Since version 18 SPSS provides comparable post-hoc tests by default.
Literature
- Bortz, J., Lienert, G. & Boehnke, K. (2000). Verteilungsfreie Methoden in der Biostatistik. Berlin: Springer. ISBN: 3540675906.
- Conover, W. J. (1971, 1980). Practical nonparametric statistics. New York: Wiley. ISBN: 0471168513.
- Schaich, E. & Hamerle, A. (1984). Verteilungsfreie statistische Prüfverfahren. Berlin: Springer. ISBN: 3540137769.
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Post-hoc comparison for Friedman test (SPSS syntax file)
Post-hoc comparison for Friedman-Test (SPSS data file)
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Hi Timo,
I have run a Friedman on PASW 18 and have the pairwise comparisons (thank you for all your instructions!).
My question is, how do I report the pairwise comparisons: are they planned or post hoc, does the test have a name (e.g., is it Wilcoxon signed-ranks?), and, what is the test statistic(e.g., χ2)?
I appreciate your help, thanks!
Halle
Hi,
the tests are simple pairwise comparisons (traditional post-hoc tests). The tests were proposed by Conover and Schaich/Hamerle (see the references for more details). There are no special name for them.
The test statistic for the test by Conover is X2-distributed and the one by Schaich and Hamerle is a t-statistic.
Timo
Hi Timo,
I was looking on the internet for a post hoc analyses for a friedman test and found your solution.
However I cannot run the syntax.
First I get a warning: missing command terminator.
My second quesions is: which modifications should i make to run the syntax with my own data?
Thanks Martijn
> First I get a warning: missing command terminator.
You´ve got a missing period '.'in one line.
> which modifications should i make to run the syntax with my own data?
Modify the two passages titled "Configuration 1" and "Configuration 2" in the syntax.
Timo
Sorry, only just noticed that they are at the beginning of the page.
Hi Timo,
thanks for sharing this online! It's a great help!! Unfortuantely I seem to be unable to get the script work for me ... Would you mind to have a look at my modified syntax file and push me towards the right direction??
Any help would be much appreciated,
Olaf.
Hi,
thanks for sharing this, would never have found this hidden post-hoc tests otherwise..
But some question remain, what test are conducted? Is there any correction applied? Like Bonferroni? What's the difference between Sig. and Adj.Sig.? Does Adj mean adjusted and that's the corrected value to use?
Sorry for all the questions, In felt so good with parametric tests and noww everything looks so different with non-parametric tests...
Sonja
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Hi,
danke für den Tipp, wie soll man die post-hoc tests denn finden wenn man das nicht gelesen hat..
Trotzdem noch ein paar Fragen: Was sind es denn genau für post-hoc Tests? Ist irgendeine Korrektur für den paarweisen Vergleich schon mit drin? So was wie Bonferroni? Und was ist der Unterschied zwischen Sig. und Adj. Sig.? Steht Adj. für Adjusted/Angepasst und das ist der Wert den man hernehmen muss um Signifikanz zu bestimmen?
Sorry für all die Fragen, jetzt hab ich zwar die ganzen parametrischen Tests und Ergebnisse versatnden aber für nicht-parametrische ist ja alles wieder anders...
Sonja
Hi Sonja,
as to the sort of test - the post-hoc tests are based on the standardized mean rank differences of the two samples. The exact formula is provided in the SPSS help under "Pairwise Multiple Comparisons (nonparametric tests algorithms)".
The column labeled "Sig." lists the uncorrected significance values. As you noted correctly, you should not use these as the multiple comparisons lead to an alpha cumulation. The column labeled "Adj. Sig" are the Bonferroni adjusted significance labels, that are calculated as p*K*(K−1)/2 with p as the uncorrected significance level and K as the number of comparisons. Use these values for you analysis.
Timo
Thanks Timo,
It worked!
Hi, Timo
You wrote that in SPSS version 18 post hoc for friedman is available? I installed the 18 version today (called PASW 18?) but could not find any possible way to do post doc? Am I looking at the wrong place?
Thanks
I forgot, of course there is no SPSS 18. Since it has been acquired by IBM, it is called PASW (but it is still the same software).
Timo
Hi Marcus,
the posthoc test is well hidden in SPSS 18:
1) Choose "Analyze" -> "Nonparametric tests" -> "Related samples"
2) Choose "Settings" and select "Friedman´s 2-way ANOVA by ranks" in the bottom, then select the option "Multiple comparisons".
3) In the output window, open the "Model Viewer" by double-clicking on the table.
4) Choose "View" -> "Pairwise comparisons" and voilá...
I hope this helps,
Timo
habe es heute noch einmal probiert und es klappte doch. Danke Stef
Hallo Timo,
meine Stichprobengröße (varcnt) beträgt 17, die sample size 16 Tiere. Diese Werte plus die Pfadangabe habe ich im syntax file angepasst, jedoch zeigt der output unzählige fehler.
Des Weiteren zeigt der Editor in Zeile 42-43 die worte compute in rot an. Ich nehme, an damit hat es ein Problem. Was mache ich nur falsch, bzw. was muss ich ändern?
Viele Grüße und 1000 Dank im Vorraus.
P.S.Ich habe die SPSS Version 18 und fand nach langem Suchen keine automatisch angebotenen post hocs. Kurz um ich bin am Ende meiner Nerven.
Hallo Stef,
so eine Ferndiagnose ist schwierig. Schick mir doch die Daten und das Syntaxfile per Email. Dann sehe ich es mir an.
Den Posthoc Test findest du in SPSS 18 unter:
1) Analyze -> Nonparametric tests -> Related samples
2) Unter "Settings" wähle rechts unten "Friedman´s 2-way ANOVA by ranks" und die Option "Multiple comparisons" aus.
3)Im Output öffnet ein Doppelklick auf die Tabelle den "Model Viewer". Unter "View" -> "Pairwise comparisons" findest du dann die Posthoc Vergleiche.
Usability ist nicht gerade eine Stärke von SPSS... :-)
Timo
Hi Timo,
after modifying the file and variable names the script runs without errors, but it doesn't produce any output. What am I doing wrong?
valjah
Hi,
I first got nothing in the output w/o error messages..
Then I tried only "integers" in the data (since only ordinal data counts) and it works!
Best,
Ron
Well, if there are no errors, than it does not seem to be a problem with the script itself but rather your SPSS settings. Check your SPSS options to display all commands in the output. Unfortunately, I don´t have any other suggestions...
Timo
i can't for the life of me seem to run this! it seems like there's lots of errors, even after modifying...
Thank you so much Timo. After editing the syntax for my dataset the posthoc tests work. Great stuff!!!
I am surprised by the totally useless file in german. I suggest next time to write it with cuneiform characters. Thanks for NOTHING.
You could have simply asked for translated instructions. I'd be happy to provide them.
But I guess, it's easier to rant about free stuff, you find on the internet, than being a little bit more constructive.
Timo
Hi Timo
Is it possible to get a copy of your syntax in english please? I would like to see what results it gives.
Natalie
I've sent them by email to you.
Timo
Hi Timo,
Thanks for post this syntax. Please may I also request the instructions in English too?
Josh
The english file is now online (see link above).
Timo
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