Re: Intepreting MANOVA and legitimacy of ANOVA
auda [EMAIL PROTECTED] wrote: : Hi, all, : In my experiment, two dependent variables were measured (say, DV1 and DV2). : I found that when analyzed sepeartely with ANOVA, independent variable (say, : IV and had two levels IV_1 and IV_2) modulated DV1 and DV2 differentially: I don't have a clue as to what you are talking about. ANOVA tests interactions, main effects, and contrasts. You have factors with levels. that's it. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Intepreting MANOVA and legitimacy of ANOVA
Hi, all, In my experiment, two dependent variables were measured (say, DV1 and DV2). I found that when analyzed sepeartely with ANOVA, independent variable (say, IV and had two levels IV_1 and IV_2) modulated DV1 and DV2 differentially: mean DV1 in IV_1 mean DV1 in IV_2 mean DV2 in IV_1 mean DV2 in IV_2 If analyzed with MANOVA, the effect of IV was significant, Rao R(2,14)=112.60, p0.000. How to intepret this result of MANOVA? Can I go ahead to claim IV modulated DV1 and DV2 differentially based up the result from MANOVA? Or I have to do other tests? Moreover, can I treat DV1 and DV2 as two levels of a factor, say, type of dependent variable, and then go ahead to test the data with repeated-measures ANOVA and see if there is an interaction between IV and type of dependent variable? Thanks, Erik = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Intepreting MANOVA and legitimacy of ANOVA
The usual problem of MANOVA, which is hard to avoid, is that even if a test comes out significant, you can't say what you have shown except 'different.' You get a clue by looking at the univariate tests and correlations. Or drawing up the interesting contrasts and testing them to see if they account for everything. I have a problem, here, that might be avoidable -- I can't tell what you are describing. Part of that is 'ugly abbreviations,' part is 'I do not like the terminology, DV and IV, abbreviated or not' so I will not take much time at it. On Fri, 18 May 2001 14:57:49 -0500, auda [EMAIL PROTECTED] wrote: Hi, all, In my experiment, two dependent variables were measured (say, DV1 and DV2). I found that when analyzed sepeartely with ANOVA, independent variable (say, IV and had two levels IV_1 and IV_2) modulated DV1 and DV2 differentially: mean DV1 in IV_1 mean DV1 in IV_2 mean DV2 in IV_1 mean DV2 in IV_2 If analyzed with MANOVA, the effect of IV was significant, Rao R(2,14)=112.60, p0.000. How to intepret this result of MANOVA? Can I go ahead to claim IV modulated DV1 and DV2 differentially based up the result from MANOVA? Or I have to do other tests? Moreover, can I treat DV1 and DV2 as two levels of a factor, say, type of dependent variable, and then go ahead to test the data with repeated-measures ANOVA and see if there is an interaction between IV and type of dependent variable? -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Intepreting MANOVA and legitimacy of ANOVA
On Fri, 18 May 2001, auda wrote (slightly edited): In my experiment, [when] two dependent variables DV1 and DV2 [were] analyzed separately with ANOVA, the independent variable [IV (with ] two levels IV_1 and IV_2) modulated DV1 and DV2 differentially: mean DV1 in IV_1 mean DV1 in IV_2 mean DV2 in IV_1 mean DV2 in IV_2 If analyzed with MANOVA, the effect of IV was significant, Rao R(2,14)=112.60, p0.000. How to interpret this result of MANOVA? Not enough information to tell. If, for example, DV2 = -DV1 + C, C a constant, you would get results of the kind you describe above. The question unanswered as yet is whether the second DV adds any information to the system. It's been a longish while since I did any MANOVAs, but I seem to recall a section of output showing step-down analyses for each formal effect of the ANOVA structure, in which each DV was reported in the order in which it had been considered, and a test reported as to the degree to which the effect on this DV was implied by the effect on previous DVs. You haven't mentioned anything about interpreting the significant univariate effects, which leads one to suspect that they are interpretable enough. What more do you think you want from MANOVA? Can I go ahead to claim IV modulated DV1 and DV2 differentially based [on] the result from MANOVA? Or I have to do other tests? THAT you can claim based on the univariate results, unless DV1 and DV2 are so closely (if negatively!) related that there is only one phenomenon occurring, rather than two: which would be one possible reason for carrying out a MANOVA. Moreover, can I treat DV1 and DV2 as two levels of a factor, say, type of dependent variable, and then go ahead to test the data with repeated-measures ANOVA and see if there is an interaction between IV and type of dependent variable? Certainly. Of course, this is not testing the same set of hypotheses as MANOVA, so the results might be somewhat different; and you have (as you have in any case) the problem of explaining (if it needs explaining) why it is reasonable for the effect of IV to be in opposite directions on the two DVs. It might be informative to repeat some of your analyses after transforming one of the DVs to (constant - old DV) . Then a repeated-measures ANOVA would tell you whether the interaction effect, present with the original DVs, involved a difference in magnitude as well as a difference in sign. -- DFB. Donald F. Burrill [EMAIL PROTECTED] 348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED] MSC #29, Plymouth, NH 03264 603-535-2597 184 Nashua Road, Bedford, NH 03110 603-471-7128 = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
