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

Brett Magill bmagill at earthlink.net
Mon Jul 21 04:12:36 CEST 2003

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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