[R] anova(cph(..) output

[pompon]

Hi,

Thank you very much for the answer.

However, I have still some misunderstandings.
from the output, can we say that plant and leaf age are significant but not
their interaction?
And the last question I promise, what would you advise me to write in the
paper to explain the different method and ackonwledge for the df?

Thank you again,
julien.

 

Frank E Harrell Jr wrote:
> 
> pompon wrote:
>> Hello,
>> 
>> I am a beginner in R and statistics, so my question may be trivial. Sorry
>> in
>> advance.
>> I performed a Cox proportion hazard regression with 2 categorical
>> variables
>> with cph{design}. Then an anova on the results.
>> the output is 
>> 
>>> anova(cph(surv(survival, censor) ~ plant + leaf.age + plant*leaf.age,
>>> Mpnymph)
>> 
>>                 Wald Statistics          Response: Surv(survival,
>> censored) 
>> 
>>  Factor                                                    Chi-Square
>> d.f. P     
>>  plant  (Factor+Higher Order Factors)             96.96     12   <.0001
>>   All Interactions                                               10.58     
>> 6   0.1022
>>  leaf.age  (Factor+Higher Order Factors)          29.11      7   0.0001
>>   All Interactions                                                 10.58     
>> 6   0.1022
>>  plant * leaf.age  (Factor+Higher Order Factors)  10.58      6   0.1022
>>  TOTAL                                           106.63     13   <.0001
>> 
>> What do "All interaction" stand for?
>> The real df of for plant is 6 and 1 for leaf.age. Then, which chi square
>> is
>> one for my main factors anf their interaction.
>> 
>> thank you,
>> Julien.
> 
> Julien,
> 
> I know what you mean when you say 'real df' but that's not the whole 
> story as plant has 6 more df by interacting with a single df variable. 
> There is no such thing as 'the' main effect test for plant.  The 12 df 
> test is unique and tests whether plant is associated with Y for any 
> level of leaf.age.
> 
> You can see exactly what is being tested by using various print options 
> for anova.Design, as described in the help file.  The "dots" option is 
> easy on the eyes.
> 
> Frank
> -- 
> Frank E Harrell Jr   Professor and Chair           School of Medicine
>                       Department of Biostatistics   Vanderbilt University
> 
> ______________________________________________
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> 
> 

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