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Can one factor overpower another when analyzing full factorial RCBD?

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Can one factor overpower another when analyzing full factorial RCBD?

[ Edited ]

My apologies for the somewhat convoluted title. Let me explain:

 

We are conducting a greenhouse study in which we are looking at plant genotype (factor A) and irrigation (factor B). Plants are grown in pots to which we randomly assigned both genotype and irrigation. The study is a full factorial RCBD with five blocks. In analyzing the data, I notice that the effect of irrigation is very strong, and I wonder if the variability associated with it overshadows potential interactions? Here is an example of analyzed data for stomatal conductance in which we took two subsamples per plant.

 

 SAS Output

 

  SAS Output
Type III Tests of Fixed Effects


Effect    Num DF    Den DF     F Value       Pr > F
   Genotype   2       50               3.06         0.0559

Irrigation    1       50      1168.62         <.0001
  Interaction   2      50              1.97           0.1506

 

Any input would be much appreciated!

 

 

David 


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2 weeks ago
Trusted Advisor
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Re: Can one factor overpower another when analyzing full factorial RCBD?

If you truly have a full factorial, then the answer to your question is NO. Each factor and interaction explains a certain amount of variability of the response, independently of the others, and so the big value you get is because the effect of irrigation is huge, and the effect of genotype and interaction is quite small.

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2 weeks ago
Trusted Advisor
Posts: 1,630

Re: Can one factor overpower another when analyzing full factorial RCBD?

If you truly have a full factorial, then the answer to your question is NO. Each factor and interaction explains a certain amount of variability of the response, independently of the others, and so the big value you get is because the effect of irrigation is huge, and the effect of genotype and interaction is quite small.

Occasional Contributor
Posts: 6

Re: Can one factor overpower another when analyzing full factorial RCBD?

Thank you, Paige. That's what I was thinking, but wanted more expert advice.
Thanks again.
SAS Super FREQ
Posts: 3,483

Re: Can one factor overpower another when analyzing full factorial RCBD?

That's the beauty of designed experiments: the factors are not correlated

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