[R-sig-eco] Testing "order" on predicted data

Corrado ct529 at york.ac.uk
Tue Nov 3 16:40:11 CET 2009


Dear friends,

the data are ordered real numbers between 0 and 1. something of that sort:

		observations
site4	0.3
site1	0.4
site5	0.42
.
.
.
siten	0.999

after being sorted. I would like the models to order the sites in the same 
order, even if the values are not right.

That is ideally:

		model1
site4	2.4
site1	2.8
site5	4.0
.
.
.
siten	32

As you see, the values are different, but the order is still the same, that is 
if I sort the values, I still get the same sorting order.

1) I do not understand how to use AIC, ROC or Spearmann in this situation!? 
Could you pleas explain?

2) I had thought about using Kendal or Wilcoxon. What do you think?

Regards

On Tuesday 03 November 2009 14:49:32 Aitor Gastón wrote:
> You can compute Spearman's rank correlation coefficient using cor() between
> predicted and observed values for each model and test differences.
> 
> 
> 
> If observed data are binary and the predictions probabilities, you may use
>  a discrimination statistic like Somers' Dxy Rank Correlation or receiver
>  operating characteristic curve area using somers2() in Hmisc package.
> 
> 
> 
> Hope this helps,
> 
> 
> 
> Aitor
> 
> 
> 
> ----- Original Message -----
> From: "Corrado" <ct529 at york.ac.uk>
> To: <r-sig-ecology at r-project.org>
> Sent: Tuesday, November 03, 2009 1:36 PM
> Subject: [R-sig-eco] Testing "order" on predicted data
> 
> > Dear all,
> >
> > I have a strange situation:
> >
> > 1) I have some data that are associated with "sites"
> > 2) I have two models that predict the data on the "sites"
> > 3) I would like to understand which of the models predicts the order of
> > the
> > data better. In other words, I am not interested in the models predicting
> > the
> > values exactly, but only in predicting values that are in the same order
> > (smaller to bigger).
> >
> > What is the best test?
> >
> > PS: Does that make sense?
> >
> > Best,
> >
> > Global Climate Change & Biodiversity Indicators
> > Area 18,Department of Biology
> > University of York, York, YO10 5YW, UK
> > Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk
> >
> > _______________________________________________
> > R-sig-ecology mailing list
> > R-sig-ecology at r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
> 



-- 
Corrado Topi

Global Climate Change & Biodiversity Indicators
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk



More information about the R-sig-ecology mailing list