[R-sig-Geo] comparing confusion matrices

[Andrew Niccolai]

Koen,

Congalton and Green 1999 ("Assessing the Accuracy of Remotely Sensed Data:
Principles and Practices") describes such a method which they term Margfit.
This method "can be applied to “normalize” or standardize the error matrices
for comparison purposes.
Margfit uses an iterative proportional fitting procedure which forces each
row and column (i.e., marginal) in the matrix to sum to a predetermined
value; hence the name Margfit. If the predetermined value is one, then each
cell value is a proportion
of one and can easily be multiplied by 100 to represent percentages. The
predetermined value could also be set to 100 to obtain percentages directly
or to any other value the analyst chooses.  In this normalization process,
differences in sample sizes used to generate the matrices are eliminated and
therefore, individual cell values within the matrix are directly
comparable." (Chapter 5).  

Dr. Congalton has sent me his Margfit application (I think it is written in
C++ but can't be sure) and I'm sure would do the same for anyone else
interested.  He can be reached at russ.congalton at unh.edu

AS for R, I bet it would be relatively straightforward to code a version of
Margefit into R.

Hope this helps,
Andrew

Andrew Niccolai
Doctoral Candidate
Yale School of Forestry
860-402-6079
andrew.niccolai at yale.edu


  

-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch
[mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of Koen Hufkens
Sent: Monday, March 09, 2009 6:19 AM
To: R-sig-GEO
Subject: [R-sig-Geo] comparing confusion matrices

Dear list,

I need some expert assistance on a geo-statistical question.

I have two maps, first and second choice classification results. And I
have two areas selected within this map. For these areas I calculated
confusion matrices.

However, I want to compare these matrices. I was considering a Mantel
test. However, I do not know if this is correct (sample sizes are not
the same so I normalized both matrices) and ideally I would love to
extract inter row differences rather than the evaluation of the total
matrix (Z-score p-value etc).

Has anyone experience with these kind of statistics (row based
comparison of matrices).

Kind regards,
Koen

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