What is an Interaction?

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*# ''Example 1'' - An interaction occurs if running speed improves by more than just the additive effect of having either an energy bar or an energy drink. For example, imagine eating a certain amount of energy bars increases running speed by 3 seconds, and drinking energy drinks increases running speed by 2 seconds. An interaction occurs if the joint effect of energy bars and energy drinks increases running speed by more than 5 seconds, such as liquid in the drink amplifying the ability to digest the energy in the bar leading to faster times.  
*# ''Example 1'' - An interaction occurs if running speed improves by more than just the additive effect of having either an energy bar or an energy drink. For example, imagine eating a certain amount of energy bars increases running speed by 3 seconds, and drinking energy drinks increases running speed by 2 seconds. An interaction occurs if the joint effect of energy bars and energy drinks increases running speed by more than 5 seconds, such as liquid in the drink amplifying the ability to digest the energy in the bar leading to faster times.  
*#:Chart 1a below shows an additive effect
*#:Chart 1a below shows an additive effect
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*#:Chart 1b below shows an Interaction.
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*#:Chart 1b below shows an Interaction.*
*# ''Example 2'' - A second example of an interaction is that alone neither variable may have an effect on running speed, such as imagining that an energy bar by itself, or an energy drink by itself, is unable to increase running speed. But, there might be an interaction effect that influences running speed when you eat the bar ''and'' drink the drink, such as the energy bar having a chemical that unleashes the power of the energy drink to increase running speed.  
*# ''Example 2'' - A second example of an interaction is that alone neither variable may have an effect on running speed, such as imagining that an energy bar by itself, or an energy drink by itself, is unable to increase running speed. But, there might be an interaction effect that influences running speed when you eat the bar ''and'' drink the drink, such as the energy bar having a chemical that unleashes the power of the energy drink to increase running speed.  
*#:Chart 2a shows when neither variable has an effect, with no Interaction
*#:Chart 2a shows when neither variable has an effect, with no Interaction
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*#:Chart 4a shows a Main Effect for the energy drink, with no Interaction
*#:Chart 4a shows a Main Effect for the energy drink, with no Interaction
*#:Chart 4b shows the same Main Effect for the energy drink, but now with an Interaction
*#:Chart 4b shows the same Main Effect for the energy drink, but now with an Interaction
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<nowiki>*</nowiki>(FYI - 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 right), but for simplicity sake they are not displayed because you can discern those graphs after identifying the major types described below).
==Graphical representations of Interactions==
==Graphical representations of Interactions==
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<table width=100% cellpadding=20>
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<td width=50% >
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This column shows the four possibilities WITHOUT an interaction:
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#Two Main Effects
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#No Main Effects
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#Main Effect for Variable A
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#Main Effect for Variable B
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</td>
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<td width=50%  valign=top>
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This column shows the four possibilities WITH an interaction:
 +
#Two Main Effects
 +
#No Main Effects
 +
#Main Effect for Variable A
 +
#Main Effect for Variable B
 +
</td>
 +
</table>
<table>
<table>
<td>
<td>

Revision as of 06:20, 8 October 2007


Contents


Interactions and Main Effects


*(FYI - 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 right), but for simplicity sake they are not displayed because you can discern those graphs after identifying the major types described below).


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

NoI2MEc.JPG

I2ME.JPG

NoINoME.JPG

INoME.JPG

NoIMEb.JPG

IMEb.JPG

NoIMEd.JPG

IMEd.JPG



Statistical formula behind Interactions




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