[R] Interpreting the example given by Frank Harrell in the predict.lrm {Design} help

[John Haart]

Dear List and Frank,

I have calculated the log-odds for my models but maybe i am not getting something but i am not understanding how for a categorical factor this helps? On all the examples i have see it relates to continuous factors where moving from one number to another shows either a increase or decrease, not as in my case a change of catagory.

Furthermore, this gives the values for each factor independent of each other, how do i get the log-odds for the entire model? I appreciate i maybe trying to put things in boxes again, i am not i am happy to report the log odds  of moving from one response level to the next but would like it for all the factors together not independently.

John
										Low		High	Diff.	Effect	S.E.		Lower	Upper
WO	Woody:Non_woody					1		2		NA	0.28	0.16	-0.04	0.6
Odds Ratio								1		2		NA	1.32	NA		0.96	1.82
PD	Abiotic:Biotic							2		1		NA	-1.21	0.13	-1.47	-0.96
Odds Ratio								2		1		NA	0.3		NA		0.23	0.38
ALT	All:Low								3		1		NA	0.47	0.19	0.11	0.84
Odds Ratio								3		1		NA	1.6		NA		1.11	2.31
ALT	High:Low							3		2		NA	-0.07	0.14	-0.35	0.21
Odds Ratio								3		2		NA	0.93	NA		0.7		1.24
ALT	Mid:Low								3		4		NA	0.39	0.15	0.1		0.67
Odds Ratio								3		4		NA	1.48	NA		1.11	1.96
REG	Two_plus:One					1		2		NA	-0.59	0.13	-0.84	-0.34
Odds Ratio								1		2		NA	0.55	NA		0.43	0.72
BIO	Arctic:Subtropical/Tropical				4		1		NA	-1.02	0.81	-2.61	0.58
Odds Ratio								4		1		NA	0.36	NA		0.07	1.78
BIO	Boreal:Subtropical/Tropical			4		2		NA	-1.21	0.81	-2.79	0.37
Odds Ratio								4		2		NA	0.3		NA		0.06	1.44
BIO	Mediterranean:Subtropical/Tropical	4		3		NA	-1.89	0.48	-2.83	-0.95
Odds Ratio								4		3		NA	0.15	NA		0.06	0.39
BIO	Temperate:Subtropical/Tropical		4		5		NA	-0.09	0.16	-0.41	0.23
Odds Ratio								4		5		NA	0.91	NA		0.66	1.26
On 3 Oct 2010, at 15:29, Frank Harrell wrote:


You still seem to be hung up on making arbitrary classifications.  Instead,
look at tendencies using odds ratios or rank correlation measures.  My book
Regression Modeling Strategies covers this.

Frank

-----
Frank Harrell
Department of Biostatistics, Vanderbilt University
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