# Thread: using within interaction, or run t-tests?

1. ## using within interaction, or run t-tests?

Hi everyone,

I have a lot of within factors for data I am analysing - it was a 2x2x2x2 within subjects ANOVA.

I am interested in one condition (called condition (repeated vs long) - that all participants had) and another condition (response: hits vs. correct rejections).

Not I can see from the output in SPSS that I am given within effects for each and also an interaction.

However, I am not sure if this interaction is near being equivalent to running two seperate t-tests (dependent t-tests) for each condition (1 t-test for repeated and 1 t-test for long) with the responses as the DVs?

Any thoughts on which to go for?

Thanks!

2. If the assumptions of the anova are met then anything you could do with t-tests you could do with the anova and you'd have a better estimate of the MSE in the anova (assuming the assumptions are correct).

My problem is I don't really understand what you're asking. Can you rephrase what it is you're interested in?

3. Thanks Dason,

Sorry if what I was asking was unclear, let me try to rephrase...

So with the output from SPSS I will be given the main effects of each within factor and also the interaction between the factors. I am particularly interested in the conditions: 'condition' (two levels: repeated vs. long) and 'response' (two levels: hit vs. correct rejection).

Rather than looking at the interaction between these two factors (which are part of a 2x2x2x2 repeated measures ANOVA) can I not just do two t-tests: the IV will be condition for each t-test, with the DV being the response (hit for 1 t-test, and correct rejection for another t-test).

Does this make sense?

Perhaps this is not really possible because by doing this I may not fully account for the other within factors that contribute to the values in the column (ERP magnitude)...

4. Well you could but I would recommend against that. You should probably do some post-hoc comparisons using the ANOVA. You should be able to get the exact tests you're looking for but you'll have a better estimate of the standard deviation if you do it using post-hoc tests with the ANOVA.

5. Thanks Dason, that's fair enough, I will probably avoid doing it...

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