What is an Interaction?

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Interactions and Main Effects


*(FYI - Chart 1b shows an ordinal interaction. A disordinal interaction occurs when the two lines cross).

Graphical representations of Interactions

This column shows the four possibilities WITHOUT an interaction:

  1. Two Main Effects
  2. No Main Effects
  3. Main Effect for Variable A
  4. Main Effect for Variable B

This column shows the four possibilities WITH an interaction:

  1. Two Main Effects
  2. No Main Effects
  3. Main Effect for Variable A
  4. Main Effect for Variable B

There are other graphical representations of Interactions and Main Effects such as effects being reduced (e.g., imagine all the graphs below being flipped down) or effects going in the opposite direction (e.g., imagine all the graphs being flipped to the left), but for simplicity sake they are not displayed because you can discern those graphs after identifying the major types described below.

NoI2MEc.JPG

I2ME.JPG

NoINoME.JPG

INoME.JPG

NoIMEb.JPG

IMEb.JPG

NoIMEd.JPG

IMEd.JPG



Statistical formula behind Interactions




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