Separate One-Way vs Two-Way Repeated Measures

Posted by João Guerreiro on Apr 29, 2015; 10:44am
URL: http://spssx-discussion.165.s1.nabble.com/Separate-One-Way-vs-Two-Way-Repeated-Measures-tp5729421.html

Hello everyone,

I'm struggling with a Within-Subjects analysis and I haven't found the answer to my doubts, so here it goes:

I have two IV (Time and Voice Conditions) and one DV (continuous variable).

Time conditions depend on the Time to Complete the task
Voice conditions refer to different voices used

                                                           Time Condition

                                         1         2          3          4          5         6
                             1          x          x          x          x

Voice Conditions     2          x          x          x          x          x          x

                             3                      x          x          x          x          x

This table shows all combinations Time X Voice that were tested, by all participants (30). For example, Time condition 1 with Voice condition 3 was not executed by any participant.

What I want with this test is to obtain the following comparisons:
- Within each Time Condition, check for differences in Voice conditions
- For each voice condition, check for differences in time condition (in particular, I want to know when does performance start to deteriorate significantly).

My first thoughts were to perform one-way repeated measures ANOVA (or Friedman due to normality violation) within each time condition; and then within each voice condition (Followed by post-hocs).

However, I found that I could analyze these two variables together with the two-way repeated measures ANOVA. I performed this analysis using the General Linear Model -> Repeated Measures menu. Yet, I found the following problems:

- I have a few combinations that don't exist (for example Time 1 X Voice 3); If I use empty values, I get no results for all the analysis... but I have to insert one variable in order to proceed with the analysis. What should I do?
- When checking for normality, almost all TimeXVoice conditions violate the assumption. I read that normality is not that strict in this test, but some of the conditions show Sig results of ,000 and almost all of them are below ,050. Should I go for a non-parametric alternative?

Is it OK to use the one-way version and analyze each of the variables separately or should I do the two-way analysis? How should I overcome the problems referred above? Should I consider a different test?

I hope I have provided enough details.
Thanks in advance,

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