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From |
"Maren Kandulla" <m.kandulla@uke.uni-hamburg.de> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: time-effect in manova (anova with repeated measures ) |

Date |
Mon, 14 Nov 2005 18:06:03 +0100 |

Dear statalist, again I am fighting with stata to do the right analysis. My data is a panel design, 6 measuring times, 4 groups to compare, n=75. I try to test whether 4 different groups differ in terms of means over time regarding a variable (motivation). In other words wether motivation differs between the 4 groups and wether there is a change over time (motivation is decreasing f.e.). First I did a nice graph to see the differences but now I would like to test them using manova. I did a manova (for repeated measures) manova motiva_1 motiva_2 motiva_3 motiva_4 motiva_5 motiva_6 = group Then I checked, which of the 4 groups differ significantly. mat c=(0,1,-1,0,0\0,1,0,-1,0\0,1,0,0,-1) manovatest, test(c) ytransform(m) mat c1=(0,1,-1,0,0) mat c2=(0,1,0,-1,0) mat c3=(0,1,0,0,-1) mat c4=(0,0,1,-1,0) mat c5=(0,0,1,0,-1) mat c6=(0,0,0,1,-1) manovatest, test(c1) ytransform(m) manovatest, test(c2) ytransform(m) manovatest, test(c3) ytransform(m) manovatest, test(c4) ytransform(m) manovatest, test(c5) ytransform(m) manovatest, test(c6) ytransform(m) This worked out perfectly. 1.) However, now I would like to see, wether there is a over-all time-effect (wether motivation is decreasing or increasing over time) for all groups together and for each group. This is very easy in SPSS but I did not figure it out in Stata even though I read different manuals and books. 2.) Secondly I would like to see wether there is a significant difference between two groups at a certain time-point (f.e. group 2 and 4 at time 3) . I could do this by using a simple anova but maybe I can integrate it in the manova-model as well? 3.) Thirdly I would like to know wether a decrease for one group differ from a certain increase of another group between two time-points (f.e. wether the decrease of group 4 between time 2 and time 3 differes significantly from the increase of group 1 at the same time period. Could you please tell me, how to write the matrix for it. I just did not understand it by reading the manual or other books. Question 1 is the most important. I know I could do Question 2 and 3 by using a form of panelanalysis, but since I am working with psychologist I would rather go for anova with repeated measures. Thanks a lot, Maren ***************************************************************** Maren Kandulla Wissenschaftliche Mitarbeiterin / Evaluation Modellstudiengang Medizin Universitätsklinikum Hamburg-Eppendorf Martinistr. 52 20246 Hamburg Tel.: ++49 40 42803 7582 Fax: ++49 40 42803 6251 Email: m.kandulla@uke.uni-hamburg.de Homepage: www.uke.uni-hamburg.de/studiengaenge/modellstudiengang/index.php * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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