[R] how to test whether two slopes are sign. different?

[Herzog, Mark]

Or better yet skip the whole "significantly" different all together, and figure out if a model with 2 slopes explains the data "better" than a model with 1------ AIC's!
 
Mark

	-----Original Message----- 
	From: Brett Magill [mailto:bmagill at earthlink.net] 
	Sent: Sun 7/20/2003 7:12 PM 
	To: Gijsbert Stoet; r-help at stat.math.ethz.ch 
	Cc: 
	Subject: Re: [R] how to test whether two slopes are sign. different?
	
	

	Not really r-specific:
	
	Z = (b1 - b2) / SQRT ( SEb1^2 + SEb2^2)
	
	-------Original Message-------
	From: Gijsbert Stoet <stoet at volition.wustl.edu>
	Sent: 07/20/03 09:51 PM
	To: r-help at stat.math.ethz.ch
	Subject: [R] how to test whether two slopes are sign. different?
	
	>
	> Hi,
	
	  suppose I do want to test whether the slopes (e.g. determined with
	lsfit) of two different population are significantly different, how do
	I test this (in R). Say for example, I found out what the slope
	between age and number of books read per year is for two different
	populations of subjects (e.g. 25 man and 25 woman), say using
	lsfit. How can I tell whether the slopes are different in R. (And how
	would I do it for regression coefficients?)
	
	Thanks a lot for your help.
	
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	>
	
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