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Jan 10, 2012 8:44 AM
(938 views)

Hi All,

Ive carried out a screening expriement looking into the effect of 6 factors on our response. I choose ro look at all two factor interactions when choosing my design. My problem is that there are a couple of significant two-factor interactions, but neither, or just one of the factors are significant as a main effect. Any ideas on what may be going on? Could the interactions be an alias for anything else?

Thanks!

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Jan 10, 2012 12:32 PM
(877 views)

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Jan 11, 2012 3:42 AM
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Jan 11, 2012 12:08 PM
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It is very possible to have significant two-factor interactions but insignificant main effects. Assuming you have a 2^k design, a main effect is the average of all values where factor i is equal to 1 minus the average of all values where factor i is equal to -1 (more or less). If the effect of factor A depends of the level of factor B so that an interaction plot looks like an X then the main effect would be 0 but the interaction would be very strong.

However, given the aliasing structure of a resolution IV design the two factor interactions that appear significant may not be the actual interaction responsible for the cause effect. I would take into account the aliasing structure and what factors appear to be significant to design a follow-up experiement that is resolution V+ to identify the most important effects.

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Jan 16, 2012 10:11 AM
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Jan 30, 2012 9:17 AM
(877 views)