I agree with dr. Zuur in as far as applying DFA to binary data-not re
I agree with dr. Zuur in as far as applying DFA to binary data-not reccomended is concerned and I am aware that other methods such as kernel DA or logistic regression may be more appropriate. Klecka (1980) and Hand (1983) pointed out that violating homogeneity assumtion is however not likely to affect the conclusions based on DFA. The purpose of the analysis I run was basically to cluster plants groups and associate them to already established lake groups and I am not quite familiar with the other methods. Are they able to do this? My data also covers other variables sets such as invertebrates richnes (with homogeneity assumtion not violated) on which I separately run DFA. However, I still have unclear the interpretation of classification function coefficients (or Fisher linear discriminant function). They represent the likelyhood that an object (variable/ invertebrate taxa) pertains to a particular class. Is in this case coefficient 0.1 (and e.g. -2) biger that -25? Thanks Dragos Dragos Zaharescu Vigo University Hand DJ. 1983. A Comparison of Two Methods of Discriminant Analysis Applied to Binary Data. Biometrics. 39 (3), 683-694 Klecka, William R. (1980). Discriminant analysis. Quantitative Applications in the Social Sciences Series, No. 19. Thousand Oaks, CA: Sage Publications. ________________________________ From: Highland Statistics Ltd. <[email protected]> To: [email protected] Sent: Wednesday, August 5, 2009 9:35:06 AM Subject: Re: [ECOLOG-L] Interpretation of Fisher's classification function coefficients of discriminant analysis On Tue, 4 Aug 2009 09:46:17 -0700, Dragos Zaharescu <[email protected]> wrote: >I run discriminant analysis on a dataset with plants speci >Hi all, >I run discriminant analysis on a dataset with plants species presence as >variables (binary, independent) and lakes # as cases. I also have a >classification variable with 4 classes. Assuming you apply "ordinary" discriminant analysis, you are violating the homogeneity assumption if you apply DA on binary data. See Chapter 14 in Zuur et al (2007) "Analysing Ecological Data", for all 10-ish assumptions of DA. >I have some problems in interpreting Fisher's classification function >coefficients. >It is said that a case belongs to the class for which the score is highest. No..that is wrong as well...see the same chapter. It is about the distance of a point to the centroids. Alain Dr. Alain F. Zuur First author of: 1. Analysing Ecological Data (2007). Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p. URL: www.springer.com/0-387-45967-7 2. Mixed effects models and extensions in ecology with R. (2009). Zuur, AF, Ieno, EN, Walker, N, Saveliev, AA, and Smith, GM. Springer. http://www.springer.com/life+sci/ecology/book/978-0-387-87457-9 3. A Beginner's Guide to R (2009). Zuur, AF, Ieno, EN, Meesters, EHWG. Springer http://www.springer.com/statistics/computational/book/978-0-387-93836-3
