MRPP: p=0.00000000

[Alin Van]

Dear all,

I have A=0,14 and p=0.00000000
I gues the problem is in too small number of plots (total 37). Cluster Analyses devides them into 6 groups, two of them have only 3 plots each. I have excluded all the rare species and species mentioned only once. Still I can't get any realistic p. Maybe I should use the data transformation?

Best,
Alina

[Bruce McCune]

Alina, I'm not sure what you mean by a realistic p. Your statistics suggest fairly strong differences between groups, despite the sample size.

The p=0.00000000 simply means that the actual calculated value is smaller than can be displayed with the number of digits available. The result could be better stated as p<0.00000001

Bruce McCune

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[Alin Van]

Bruce, thank you very much!

I have another question about p values in PC ORD - does the p value as a result of randomization (p = (1+number of runs ≥ observed)/(1+number of randomized runs)) show the significance? in my case the significance of the indicator value in Indicator Specie Analyses, and  if p≥ 0,05  indicator value is not significant?

Many thanks,
Alina

[Bruce McCune]

Alina, the special characters you used did not come through. But if p > .05 then the IVmax for that species is not significantlyl higher than expected by chance. (assuming you are applying the traditional cutoff of alpha = .05 for probability of a type I error).

Bruce McCune

At 09:37 AM 6/21/2013, you wrote:

Bruce, thank you very much!

I have another question about p values in PC ORD - does the p value as a result of randomization (p = (1+number of runs ≥ observed)/(1+number of randomized runs)) show the significance? in my case the significance of the indicator value in Indicator Specie Analyses, and  if p≥ 0,05  indicator value is not significant?

Many thanks,
Alina